30 December 2009

Calendario Contest VHF/UHF/SHF Italia 2010 per agende elettoniche

Finalmente, dopo due anni di pausa, per il 2010 sono riuscito a pubblicare il calendario dei contest VHF&up in formato vCalendar che consente l'importazione sulle più diffuse agende elettroniche: online, su computer e su telefonino (direttamente o tramite sincronizzazione con il PC).

Si può scaricare il file dalla home page del mio sito www.paolocravero.tk. Ho anche approntato una miniguida per chi usa il Google Calendar, prelevabile in PDF allo stesso indirizzo.

(EN/US: I have published in vCalendar form the Italian VHF&up Contest Calendar 2010. It's on my main website. It allows to load contest data into electronic organizers, online, local or handheld.)

17 December 2009

Stuck with 50 MHz QRP TX

I have been thinking for a week how to proceed on my 50 MHz TX and I haven't decided yet.

I have one fixed frequency transmitter that puts out some 30mW CW that I could turn into AM (or DSB). This would mix digital circuits with analog transistors.

I have another transmitter on a single chip, XTAL based so that it can work on FM. It's a neat design, it doesn't want to emit a proper 50 MHz harmonic but rather generates weird multiplication factors.

I have spent a good amount of time trying to make the FM TX work, actually to multiply correctly, but I also want to get on the air with an homebrew voice transmitter and AM is the closest...

I will have few more sleeps on this :-)

11 December 2009

Back to WSPRing

These days my RTX setup is collecting dust, mainly because 30m are closed when I would be able to use them (after 22Z). So I decided to spare some electricity and see who could be received in WSPR in this season.

After seeing always the same calls on 30m I tuned to 40m and with my surprise there were a lot of signals, even if my antenna is supposed to be single-band for 30m. On 40m I decoded both Brazil (5W) and Australia (10W).

One disappointment: most reported stations were announcing power levels of 5W or more, with one WSPRing at 50W, wiping out the braves running 1W or less.

WSPR is not a QRP mode. QRP is in operator's brain! Sirs, turn down your power!

09 December 2009

cdzservices.exe hanging mobile devices (mSuite sync problem)

Note: this is a service information not really related to my usual lab activities, but I found no mention elsewhere in the net. I hope to help someone...

On 2009-11-19 the mSuite client on my Windows Mobile smartphone stopped synchronizing. Worse, something hanged the device eating up all its CPU, making it very non-responsive, almost useless.

Looking at running processes I saw that cdzservices.exe was the culprit. It belongs to Commontime mSuite software. It hangs because the Commontime CA certificate has expired on ... 2009-11-19!

So, work with your internal helpdesk and find the new certificate, install it on the mobile device and hopefully it should start synching again. I haven't gotten the new certificate yet! No mention on the Commontime website!

Please post a comment if this post helped you. Thanks.

07 December 2009

My 6m FM TX

Looks like I have finally gotten around the proper deviation for a 50 MHz FM TX, but many problems still have to be tackled down.

I tried to "select" the desired harmonic with the RLC circuit found on a paper online and I had to play a lot with L and C values. The L was wound on a T50-6 core, while C was a 3-16pF trimmer. On the frequency meter I could read 2x XTAL fundamental and a weird 2.5x, depending on trimmer position. After removing almost half of the originally planned turns and making extensive use of the oscilloscope, the output frequency is now steady on 50 MHz.

I even noticed that the frequency changed when loading the "PA" (note that a buffer gate is between harmonic selector and PA), so I did the fine tuning with a 7dB 50ohm attenuator pad and a 50 ohm dummy load.

On the oscilloscope I can read almost 3V peak on the dummy load, which is about 80mW or +19dBm. Given the 7dB pad ... +19+7 = 26 dBm that is 400mW of RF. Not bad for a 74HC240 chip pulled at its operating limit!

In order to minimize stray capacitances I moved components around and now both AF and RF sit on the same copper ground.

It's time to add an LPF and ask for an online report! After a check at the spectrum analyzer, of course!

02 December 2009

Which RX for my 50 MHz QRPp FM TX

I received this question from Pedro, a LU HAM: "What are you planning to use for the 50 MHz FM project receiver?" Here's my answer to him.

Originally I planned to use the TDA7000 chip but configured at NBFM it is not good according to SM0VPO.

Then I switched my mind to TBA120, an FM IF chip from TV sets that works better but it works up to 10 MHz (or somewhere there). Since my TX is single-frequency, as the original SixBox, I thought of using a 50.0 MHz canned oscillator to feed a mixer and tune my IF at 800 kHz (my TX XTAL is 16.934 MHz or so).

Last chance is to use a direct conversion receiver and agree with the other station will reply in SSB or AM, so working a mode-split QSO. I am not planning to build two (R)TX to talk together!

I don't have a diagram of the TX yet. It is based on 74HC240 chip:
- one gate oscillator
- one gate buffer with LC output tuned on 3rd harmonic
- one gate buffer
- 4 parallel gates as PA

The second buffer could be removed but then the 4 parallel gates give about 14pF or capacitance, which is too much for the LC.

I have measured about 28mW at the output of a single 74HC86 gate, so hopefully 4 HC240 in parallel can deliver more, even if at 50 MHz (operating limits).

Let me know if you have some ideas for PA and/or RX!

30 November 2009

A classic VXO with a CMOS gate

I have been captured by the fact that a TTL/CMOS gate can serve as a XTAL oscillator, as well as frequency multiplier. That was few years back. Now my crazy idea of building a 6m FM transmitter took me into the world of homebrew voice communication, whereas I have always limited myself to CW.

The CMOS oscillator is available on all datasheets and seems to be pretty reliable. I have also found on my high school book formulas for computing both loading capacitors and resistor! (in a soon-to-be-published article in this blog)

Once I solved the SixBox microphone amplifier clipping distortion (too much amplification), I had to get a proper frequency deviation for 6m NBFM: about 9 kHz on 50 MHz, that's 3 kHz at the XTAL fundamental frequency.

I tried different varicaps, from a BB105 to a IR LED through ordinary 5mm RED LED. In order to measure VXO frequency change I drove the varicap through a resistive potentiometer. The XTAL had a 4.7uH molded choke in series, to reduce the overall oscillator Q. The following diagram plots two configurations:

(The vertical axis is in kHz, while horizontal is the reverse voltage applied to the diode.)

"Config A" had 115pF load plus the BB105 plus the 4.7uH.
"Config B" had 33pF load plus any diode plus the 4.7uH.

In both cases the varicap is in series with a 100pF DC blocking capacitor.

Curiously the same values of "Config B" were obtained with a BB105, a 1N4003 and several LEDs. The usable deviation at the fundamental frequency is about 1.6 kHz, which results in low and distorted modulation at 50 MHz.

In another attempt I repeated these tests without the molder choke and the swing was even less. This effect light up a possible solution: use a larger inductor in series with XTAL!

When I replaced the 4.7uH with a 10uH choke the swing extended to 3kHz at the fundamental frequency, with the same curve as shown in the picture above.

Where do I stand now? I have the ability to obtain a proper deviation at 50.7 MHz but I have to restrict the varicap modulating voltage between 7-8V and 10V.

18 November 2009

Electret microphone output

For my reproduction of the FredBox/SixBox I wanted to know how much voltage output to expect from an electret microphone. Actually my mind is already on a 6m QRP FM transmitter, but the output swing is good to be known.

The oscilloscope comes handy for this kind of measurements. A resistor, capacitor and a surplus electret microphone do the job. Then, speak into it. Oh, don't forget a power supply!

My daughter really enjoyed screaming into the microphone and observing changes on the o'scope screen. I couldn't have tested it without her.

At her loudest scream the microphone outputted 200mV peak. On the DSO she also learned which button would freeze the trace. It was a very instructive experiment for all of us!

16 November 2009

When conditions are good ... P2!

I need to share my luck last Friday when I worked P29CW on 30m CW using the FT-817 at 5W and my homebrew balcony antenna at 8th floor (picture1 and picture2 of the antenna).

I headed to the 30m QRP calling frequency, but some rare station was having a pile-up. Another pile up was found on the 10.12x MHz. So I tuned the band for some lone CQ'er and heard this P29CW at 15-16 WPM, 559 to 599 ... I copied the callsign 10 times since I never heard of such a prefix. I replied and he came back with IZ1Z? I sent my call twice and we exchanged reports.

Since I thought he was some European special prefix I didn't mention I was QRP.

Then I opened a paper on my desk that lists countries without a QSL bureau and there it was: Papua New Guinea. What a night!

That was 13800 km with 5W out. The antenna might have an efficiency of 50%, making it a 0dBi radiator according to some simulation software.

So, real QRP DX is possible when conditions are good: it's just that both propagation and crowd need to cooperate. :-)

Now back to my version of the SixBox.

12 November 2009

FT817 keypad - first quirk solved

I produced a new firmware version that fixes the quirk reported in the previous post (mode not changed when recalling an onboard memory on a "far" band). It now uses a larger delay in the command sequence (200ms instead of 100ms) and the FT-817 seems to be happy with it and behave as expected.

All firmwares released since 2009-November-12 will carry the new delay. Freely available firmware for download will be updated shortly.

Thank to Cristian in YO-land for reporting the non-blocking issue.

10 November 2009

FT817 keypad - first quirk reported

A builder of my FT-817 keypad has reported me a problem using onboard dynamic memories and "far" QSYs. It was reported while testing a 38400 baud keypad version (default is 4800 baud), but the glitch is caused by RTX internals and not the keypad firmware itself.

I could reproduce the same behavior but not deterministically! Try it yourself:
  • write 3700 kHz LSB in onboard memory #1
  • write 145500 kHz FM in onboard memory #2
Set your VFO to, say, 20m band. Recall memory #1, then recall memory #2: it might happen that the mode stays LSB and doesn't change to FM.

Quick fix: recall memory #2 and the mode is set properly.

Cause. I think the internal CPU of the FT-817 is busy doing something else when asking for a large QSY and ignores the mode change command. The 100ms delay between the two is not enough.

Fix: new firmwares include a 200ms delay that seems to make both the operator and FT-817 happy.

Freely available firmware will be updates shortly.

Since this glitch is non-blocking for keypad functions and doesn't hang the radio I will not issue a recall statement for already shipped chips.

04 November 2009

Doubling to 6m and filtering

Previous measurements on my base oscillator for a simple 6m TX were encouraging and I started thinking of making a DSB transmitter instead of AM. I added a parallel LC circuit at the output of my EX-OR mixer/doubler and started seeing an improvement on the oscilloscope.

Then I checked at the spectrum analyzer and results were encouraging.

Frequency After LC [dBm] Delta [dBc] Before LC [dBm] Delta bef [dBc]
50,35 7,5
75,53 -29,5 -37

100,7 -14 -21,5 -6 -11
125,88 -17 -24,5

151,05 -33 -40,5

The 50 MHz output on 50 ohm has increased to 7.5 dBm (through the 7dB pad means 14.5 dBm = 28 mW) and I can tune the delay line to almost kill the 75 MHz product while keeping all other harmonics more than 20 dB below the carrier. Before adding the LC the second order harmonic was down 11 dBc, another positive improvement.

Now I have too many options:
  • try it on the air as a CW transmitter
  • build a PA and AM-modulate it
  • feed this signal to an NE602 and generate DSB
In any case I need to start working on the low frequency part.

29 October 2009

Doubling to 6m

SPRAT 140 magazine had an article by G3XBM's Sixbox 50 MHz AM transceiver. It is also documented on this blog/website. His TX is a 3rd overtone XTAL oscillator followed by a buffer and an amplifier both voltage controlled to generate AM modulation. The RX is a freerunning LC regen. The output power is about 200mW peak (modulated).

I got intrigued by his simple circuit and decided to replicate his design.

It turns out that I have one surplus XTAL that would put me on 50.8 MHz and a canned oscillator that goes to 50.35 MHz. All simulations were done using my xtalfind Perl program.

The XTAL has too short leads to be used and it is not an overtone cut, so I decided to use the 25.175 MHz canned oscillator and try to double it with the EX-OR doubler described in the previous post.

The local oscillator signal has a period of T=40ns. I need to delay it of 1/4T, so 10ns. According to the 74HC86 datasheet this amount is right in the typical propagation delay range for 5V supply.

I've assembled dead-bug the circuit and done two tests:
  1. check the output at the oscilloscope (max BW 100 MHz, so quite at the limit)
  2. use my finger to check for the base frequency
  3. see the output spectrum on a spectrum analyzer

Test #1 is visual. The resulting waveform is more sinusoidal than it actually is because I've operated the instrument at the limit of its bandwidth. But the output period is half the input, so there's no 25 MHz output.

Test #2 confirm. Using my FT-817 receiver tuned on 25.175 MHz carrier I touched the canned oscillator output and noticed a signal increase. Then I touched the 74HC86 output and heard only an increase on 50.35 MHz.

Test #3. My spectrum analyzer starts at 45 MHz, so I have no mean to check what happens at the LO frequency. But I measured 5dBm at 50 MHz (through a 7dB attenuator pad) and about -6dBm and 100 MHz.
Curiously there was a rather strong product at 75 MHz that I could null adjusting the delay line.

So in theory I have a 12dBm signal (15mW) at 50.35 MHz. I could directly modulate the 74HC86 chip to produce AM, but the propagation delay is a function of Vcc too.

Now I can either generate AM or DSB-SC. Both need a linear amplifier chain, with DSB being more energy efficient. Since I have a digital signal I could probably drive a simple balanced mixer, or an NE602. In case I use a NE602 then it can be re-used as RX mixer too (for AM or SSB, not DSB).

If the canned oscillator could be pulled I could generate NBFM too, but I think this is not the case.

28 October 2009

The EX-OR frequency doubler

After few years I've had this idea in mind, I could finally melt some solder and put together a frequency doubler using EX-OR digital gates.

The idea for my application is: feed a 2-IN XOR gate from a 74HC86 with properly phased signals and it generates a 2 * f_in (square) wave.

So, what are "properly phased signals"?

If the base frequency f_in, which is in form of a square wave, is delayed of T/4 and fed to the second input of XOR gate, then given the XOR truth table the gate will output a 2x frequency.

I leave the reader draw the two wave forms and XOR them graphically to see the effect.

How to delay the square wave then? Easy, use the intrinsic propagation delay of digital gates! Per datasheet a 74HC86 gate has a propagation delay of 11ns with a load of 50pF at 6V supply. According to another document of OnSemi the delay introduced by a gate varies linearly with the capacitive load, so I see a simple way to control delay between 50ns down to 5-6ns.

Why am I doing this? Besides for the scientific progress :-) I'm aiming at a simple TX/RX system for 50 MHz band.

26 October 2009

FT817 keypad - a completed one

I have built one of my FT-817 keypads for another person, and here's how it looks like when unassembled:

I have included connectors on the serial cable and on both LEDs. All connectors are different so the user will not mix them. The overall footprint of the completed keypad is slightly larger than the matrix keypad itself, which sits on the circuit using a matched pin-header strip.

Except for the book, what is shown is worth 20€ (@2009) of materials and circa 3 hours of work.

08 October 2009

DTT switch-over

2009-10-07: switch over from analogue over-the-air TV to digital (DTT, DVB-T) in my area.

I grabbed the TV remote control and scanned all programmed channels, from 1 to 29: white noise. I ran a complete search in case the condo antenna could pick up some remote signal once masked by stronger local stations: nothing.

RIP analogue TV.

I still have to erect my antennas on the roof. With digital TV signals it will be harder to identify even the lightest TVI, or perhaps the whole system will more immune. At least people won't hear my voice or CW through their TV set loudspeakers, just loose audio or video quality.

Maybe some analogue TV will be thrown away, becoming a good source for scrounged parts to keep aside for future experiments.

17 September 2009

Inside Gould 4072 DSO

In August this year I have received a Gould DSO model 4072, 100 MHz bandwidth, 400 MSPS. It is a totally different concept of oscilloscope to what I am used to (analog), and without documentation it needs some thorough exploration.

The unit appears to be in working conditions, except for the power button that doesn't depress and perhaps broken CRT graticule illumination (don't remember).

According to the OSD menu this DSO has onboard memories for measured waveforms, so it must have a backup battery somewhere. I opened it up removing the upper lid (careful with the printing device connecting cable!) and was surprised to see that it has plug-in boards.
I wouldn't say that these are serviceable, but at least replaceable with similar boards.

With a bit of lucky intuition I found the battery on the "DIGITAL" board. It is 2.4V 110mAh and according to my DVM it still has some charge (~1V). No visible leak. I will replace it as soon as possible.

At the same time I am working on the power button, that seems to close only one contact towards the chassis (!). Or wait, it must be some mechanical thing instead. The button pulls/releases a metallic strip that goes all the way to PSU. I need to follow it all the way in there...

Edit 2014-02-11: I do not own anymore the Gould 4072.

03 August 2009

QRP from Rab Island (2009)

This note will look old, since more than one month has passed since we've returned back home. But at least will report what I have done in 2009 on Rab island.

I had planned to take part to Apulia VHF QRP contest from the top of Kamenjak mountain. All I could carry was the 4 element Yagi. The day before the contest I had forgotten headlight on and the car battery went flat dead. Fortunately I could get it started for 100 HRK from the local service station.

The contest day I went up to the top, prepared the setup and called for two hours beaming Italy (organizing country) without receiving a single reply.

So I decided VHF was not the way to go and I switched to HF 20m. I moved the 9m fishing pole away from the car so it could support the 20m EFHW antenna radiator, tuner laying on the rocky ground and one counterpoise.

I did get odd looks from hikers/bikers/tourists passing by, but nobody asked a thing.

The band was crowded, signals were good, so I tried some QRP SSB contacts. I could work one station, others were having pile up (it was too hot up there for fighting). Finally I fired up the netPC and called CQ on PSK31. This mode was more productive.

The game was soon over since we were expected for lunch. PSK31 operations continued from home with 100% battery power (RTX and computer) and 20m EFHW antenna out of the balcony.

Overall I managed fewer QSOs than last year, but I did not take part in any contest. There was no pile-up on my calls even if I was from a IOTA/IOCA reference.

I missed the warmth of CW contacts but I enjoyed these operations nevertheless.

Alpe Adria VHF 2009: mission aborted

Every year I can hardly wait for Alpe Adria VHF contest, the first Sunday in August. After my best performance of year 2008, I wanted to improve the setup.

I started building a Yagi with 4m long boom: on an empty mountaintop it should still be possible to handle it. On Friday the boom was ready but not the rest (dipole, elements, ...). Moreover one battery pack is not suitable anymore for my FT817, so I had half power reserve than last year.

I decided to keep things simple and short: same antenna as 2008 (5el on 2m boom) and just one battery pack. I would not be able to beat my own A.A. record but at least to improve my operating skills.

On Sunday morning I drive up to Colle delle Finestre (2100 masl), there are some clouds in the sky but don't look too serious:

Once at Colle, I see dark clouds climbing fast from the other valley, and my target destination already covered. I change plan: I'll go to a closer peak at 2500 masl.

At the beginning of my hike I have to pass a barrier, I pull my backpack, I pull ... crash ... damn! What was that? I put the backpack down and the 2m long boom sticking out of it has broken in two. I can still build a 3 el antenna or fix it on the fly once on top. So I continue hiking.

Air gets colder. I feel something on my hand: it starts raining.

Far away I hear a couple of sounds that look like a thunder, or a motorcycle roar.

-> abort <-

I walk back to the car, take few pictures and a strong storm begins. It lasted two hours, so I am glad I decided to return home rather than wait for clouds to pass by.

See you next year, Alpe Adria!

30 July 2009

The word of experience

Finally I put my Tek 7603 oscilloscope into service. A friend (the one from optical experiments) needed to verify a circuit he's building. Those were routine tests, not troubleshooting.

While probing for a couple of signals (ca 3 kHz, 15Vpeak) I noticed a strange random behavior: either the signal was as expected, or was passing through a high-pass filter (only spikes instead of edges).

The first problem was easily tracked down to a cold solder joint since it showed properly when touching the generating IC.

The second ghost was trickier: all joints were ok. It was a digital signal... where was the high-pass effect coming from? While checking for continuity with an ohm-meter backwards from target to source pins (with ICs removed!) I came to a homebrew connector with 2.54mm (1") pin headers ... on the corresponding pin tip I could not get a proper contact, while at the pin base it worked alright. Very suspicious. I touched the pin and asked right away: "what did you do to it? Glue?"

He admitted that the building instructions showed a way to hold the strip while soldering: put it into a roll of packing tape. !!!!!!!!!!!!!!!!

21 July 2009


After shooting the long wave NDB (non-directional beacon) CAS, I happened to have the chance to shoot another NDB in Croatia.

It is NDB ZAG, whose coordinates can be found on Internet. Unfortunately I had forgotten to plan in advance the road to get close to it, so I asked my brother back home to send me some info via SMS. It turned out that Internet is far more detailed than any other paper map I could locate and I failed to reach the NDB location.

I had to blind shoot it while driving at 90 km/h on the high speed road going to Vrbovec. It sits North of that road. The digital SLR helped to get the antenna into the frame.

This second picture is cropped from a 10Mpixel image and digitally zoomed 3 times.

After these shots I tried without success to get close to the beacon site, but nothing. Village names on Internet are not written anywhere in the real world! Now I've checked through a web service with satellite pictures how to get there, so perhaps I'll try a second approach on our next trip to Zagreb.

19 June 2009

BPSK splatters

I had not seen such a bad signal yet in my digimode life. 30m, BPSK63, 2009-06-18. I did everything on my FT-817, IPO, ATT, volume control but to no avail: I could still see the signal twice and with many distortion products.

I worked him with 1W, so his signal was indeed very strong. I mentioned the bad IMD (-15dB) but nothing changed. I gave RSQ 555 but should have been 591.

A couple of hints:
Make sure the ALC is not active when transmitting. With ALC=0, just below its ALC>0 point you are already transmitting at full power. After that ALC reduces your audio drive, creates non-linearities in the TX chain and sends out splatters. Moreover with ALC>0 your measured power is distributed amongst all unwanted signals, thus you actually reduce your main signal power (see below)!

Transmit above 1500 Hz in the waterfall. This helps not to send the signal twice. If you sit at around 1000 Hz, your TX SSB bandpass filter will let through 2000 and 3000 Hz too, so you'd transmit any harmonic generated within your computer of first TX audio stages. Better stay between 1500 and 2000 waterfall Hz, and retune your RTX main dial. This is a clever hint that I have not seen mentioned anywhere.

"below". A proof that his distorted 50W did no more than my 2.5W comes from pskmap: we both reached the same stations, including one in the US East Coast.

18 June 2009

Console switch

Have you ever come across a keyboard+mouse+VGA mechanical switch? I have found a 4-way model (4 computers, 1 actual device) and couldn't resist to look inside it.

It is routing about 25 lines. The solderwork look done by hand and with just one color of wire! Hats off!

Any use in the shack?

16 June 2009

2 x Balcony QSO

Funny enough to report it here. Last night I was working 30m PSK31 when a Mr. Enzo from Paris came back to my CQs... after the usual data exchange it turned out we were both using an antenna on the balcony. Him 80W, me 5W, 100% copy on both sides. Moreover he is Italian, according to his qrz(dot)com profile.

I think that was my first BPSK31 2xBalcony QSO. HI.

It is almost time to open a club and give awards, HI.

12 June 2009

EFHWA tuner quirks

For the upcoming Summer holidays I decided to try something new: an End Fed Half Wave Antenna (EFHWA). Since all operating conditions will be known (same place of last year), I should be able to compare two different antennas.

I chose the EFHWA because it is reported to have a decent radiation angle even when low above the ground. This antenna has a high impedance between 2500 and 5000 ohm depending on the way it is installed, so it requires a matching device.

Given I will be using QRP, I built a transformer on T50-2 code with 3:27 turns ratio. This 1:81 step-down impedance transformer matches 50 ohm to ca 4000 ohm. With a polyvaricon capacitor it tuned between 6.2 and 22 MHz.

Then I reduced the turns ratio to 3:25, so that it would match a 3300 ohm antenna, in between the EFHWA expected Z ranges. This increased the resonance to 9-26 MHz since the secondary inductance had reduced. Good 30 to 12m coverage, I wouldn't be able to throw a 20m of wire for a 40m EFHWA anyway.

Ready for boxing the tuner... surprise! The tuning range has now shrinked to 11-26 MHz! I have lost 30m when fitting it into a plastic box. This means that the maximum capacitance or inductance available has reduced (I did shorten wires of 2-3 cm if that matters), or both. Need to get back to it and try something different.

For those interested: I found out the tuning range using an antenna analyzer (MFJ259B) and connecting a 3k3 resistor in place of the antenna. Gave full capacitance and looked for the SWR dip with the 259. Same at minimum capacitance.

11 June 2009

CW vs PSK vs FeldHell

You might have read of my recent interest in machine generated modes (or "digital modes"). Lately I have filled my logbook with tens of PSK31/PSK63 contacts and one FeldHell. All on 30m with 2.5W power output into the horizontal base-loaded monopole antenna.

One night I could not get any contact in PSK31, so I got bored and moved to the CW part of 30m, where I collected 3 QSOs. All their sigs were 599 on my meter, including that UK HAM that was running 5W.

So, CW wins over MGMs? I did an Internet search and found references to a work of Tony K2MO (search it yourself). Besides his measurements, he published a minimum Signal-To-Noise ratio for error-free copy, where CW 20WPM scores -13dB, PSK31 -10dB, PSK63 and FeldHell -7dB.

The lower SNR, the more noise is accepted for error-free copy. So, CW@20wpm is more robust than PSK31. Given the 3dB difference, I need to double the power when doing PSK31 to obtain the same CW SNR. One more double for FeldHell.

So: CW 2.5W, PSK31 5W, FeldHell 10W.

In theory of course.

28 May 2009

First Feldhell QSO

Looks like I need to move further very often. So from bpsk I tried feldhell. Nothing special about it, but I like its resilience to QSB. Moreover it leaves a lot to the brain for decoding, since it is a "visual" mode of communication. And apparently it works at 2.5W too!

The skip was about 7-800km that night, so SP9 right in the active area. The screenshot shows both my transmission (upper part) and how I received SP9. Note the discontinuities in his signal due to strong BPSK transmissions (visible in the waterfall on the RHS) and a local QRSS beacon.
Nevertheless his text was readable and the QSO could be completed. I should have tried with the narrow filter, and I need more practice in tuning hell signals.


27 May 2009

Shoud I buy an FT-817? QRP lifestyle

On an Italian HAM forum I replied to a person that owned an FT-817 for one week and then sold it, now considering to buy another one. I think it is worth copyng my words on my blog too. For non-Italian language readers, please use an online translator to get an idea of what I said.

Il QRP è uno stile di vita, è molta tecnica operativa e soprattutto molta pazienza.

Se il tuo obiettivo in radio è lavorare il DX senza troppa fatica, allora no, il QRP non va bene. Non è vero che le chiamate QRP hanno la priorità, al massimo il corrispondente si fa leggermente più paziente. Ma "ZYW QRP" non buca i pileup.

Se invece per te la licenza HAM è uno strumento per imparare, il QRP ci può stare. Ma lo puoi intraprendere anche solo riducendo al minimo la potenza del tuo RTX usuale, senza investire nell'817.

L'817 è un quadribanda comodo perchè facilmente trasportabile e consente di sperimentare antenne e attrezzature da campo, ma non allevia delle fatiche del QRP.

Io mi accontento di lavorare quelli che mi sentono (in HF) e di ottimizzare la stazione per migliorare la performance (contest VHF esclusivamente portatili a spalla). Così mi stupisco molto quando mi ricevono negli USA con 5W CW e l'antenna che fuoriesce dal balcone.

My opinion, of course.

23 May 2009

More on the netbook for shack use

One more thing I realized last night is that a SSD-based netbook is extremely quiet. It emits no hiss whatsoever, I doubt it has a cooling fan either. Disk capacity is limited to the size of the onboard card + any SD card you add (4-8-16-32 GB), but it poses no real problem if used for logging and digital modes terminal.

Just remember solid state disks (SSD) have a limited amount of read-write cycles, so backup often your data!

Does anyone know of RFI problems to SSD?

22 May 2009

Daytime view of my (30m) antenna

Since I believe digital mode operators are more online than usual CWers, I might receive more visits of QSO partners interested to see my "base loaded horizontal monopole sticking out of the balcony at 8th floor". After deep winter shots, here you are a Spring morning view:

The fishing pole points towards N-NE.

21 May 2009

Netbook (eeepc), FT817, digital modes

Our Summer holidays will take place on the same location of last year, just one week later. I already know the lodging, surroundings and somewhat, propagation too. Last year I did only CW QRP with a total of 56 contacts. The most limiting factor was operator's conditions, that became a lousy CW'er when tired. So this year I will (might) try digital modes.

I borrowed a netbook computer (eee PC, if you prefer) to check how it would perform. It is an Asus machine with 8.9" 1024x768 display On WinXP I installed Digipan, MultiPSK and WSPR as a starting point.

First test was with WSPR after syncing the clock (Dimension4). This netbook has enough computing power to keep up with the DSP/FFT analysis of WSPR slots (2 minutes). It takes 1'35" to digest two minutes of capture (one WSPR cycle), so the CPU runs at full steam 75% of time.

Then I tried to play with PSK31. I looked at MultiPSK because it supports several modes, but I was scared by the plethora of configuration options and the buttons density on the small 8.9" display. I tried a transmission test in my headphones but the signal was distorted. Discarded.

I moved on to DigiPan. I had used it in the past, so I am slightly familiar with its user interface. I love the multichannel reception capability. It sounds good without clicks or hum. CPU load is not excessive even with the multichannel scroll.

The keyboard of these netbooks is small. You need small fingers and a bit of practice to type fast without errors, so better plan good macros in advance.

This 6-cell battery (660mAh) lasts longer than I can afford to stay on the air, so the setup is probably valid for portable, exclusively battery powered, operations.

The same netbook also has Ubuntu 9.04 installed. I added HAM radio packages through the graphical interface and they load fine. Unfortunately fldigi transmitted signal sounds very bad and I could not understand how good the CPU usage is. I think I will stay with WinXP.

By the way, I used a fully isolated audio interface between the FT-817 and netbook. Since netbook has no serial/parallel port I kept my RTX in USB mode and used the VOX function. All signals picked on the FT-817 side Mic/Ear sockets.

18 May 2009

FT817 digimodes

We (family) are planning our Summer holiday. We will visit the same location of last year (IOTA EU-136, IOCA CI-096), with one more child onboard. Radio time might be even more limited than July 2008, and/or operator's energies further reduced.

A tired operator is a very lousy CW'er, so I am considering to try digimodes this year. SSB is out of question because it is too noisy and not effective at QRP levels.

I had once built a fully-isolated general-purpose soundcard interface. I also had prepared a cable to interface with FT-817 through the MIC/earphone plugs so that I could use VOX (VOX works only on the MIC plug, not on the rear DATA connector). But a strong hum was coming out together with PSK signal. After a lot of debugging and a bit of soldering I mentally re-counted the purpose of 8 wires in the FT-817 MIC cable: up, down, mic, gnd, ptt, fast, +V... what was the eighth? A brief look at the manual revealed a "mic gnd" line.

According to the schematic diagram, both "gnd" and "mic gnd" lines are grounded without further processing. But apparently they are not grounded right away near the plug.

Once I had connected both to my interface ground line the hum disappeared and I could complete two PSK31 QSOs. ALC down to zero, power to 5W.

Now I need more digimode practice and some macro review.

12 May 2009

Still no luck 6m mobile

It has been two weeks since I have started carrying my FT817 to work. The plan is to take advantage of ES openings while driving home>office and back, but so far I have had no luck: band closed.

I am active between 0600z > 0620z and 1520z > 1600z circa, usually calling /M around 50.155 MHz in JN35.

Funny episode this morning at a traffic light, when behind me stopped a car with a permanently installed CB antenna. My 6m antenna is a modified CB magmount whip. His plate on the windscreen evidenced he is a CB'er, but he horned lightly and cheered. I waved back and felt like a specie in risk of extinction.

All my sympathy to mobile radio enthusiasts, HAMs and CB'er.

28 April 2009

Empirically obtain the vertical radiation pattern

How would you study the vertical radiation pattern of your omnidirectional antenna? You'd need a signal source flying over the antenna at any given angle, far away.

For VHF and UHF antennas you may find that HAM satellites are handy for this task too.

Depending on your location, some LEO bird will pass over your antenna at a good selection of elevation angles. The best pass is one that puts the satellite as much above your head as possible. An FM satellite is even better, since it provides a carrier of constant power, like AO-51 downlink on 70 cm.

So, make a prediction of an usable pass. Don't forget to check the satellite operating schedule, if any. Draw or print or write down a selection of time, elevation angle and frequency +/- doppler. Azimuth is not relevant if your omnidirectional antenna has a clear view of the horizon. Sit back and wait. Then look closely at the S-meter (better if analogue).

So far I have received AO-51 UHF downlink on two antennas, one shorter than lambda/4 and one 3/4 wave (a VHF whip). Both magmounted on the car. At a certain point I noticed AO-51 signal at S2 on my S-meter with the VHF whip, as much as I could get with the Moxon beam!

Back to the computer, I used MMANA to simulate this antenna at UHF. It was not a surprise to see that at 45° elevation this antenna has a 5.5dBi gain. Moxon rectangles are said to have about 6dBi gain, so we're in the ballpark.

As a conclusion, I can say the 3/4 lambda at UHF is good to receive almost any AO-51 pass above 10°. Unfortunately it is not enough to hit the satellite repeater with 5W. With a proper S-meter, the vertical radiation pattern of an antenna can be drawn per-points.


If you were having a CW QSO with me and received a sudden "SRI QRT", as SP3DGV got last night, it means I had to run off to the youngest child because she woke up and needed assistance (ie woke up and started crying for whatever reason).

Radio time is very limited these days, and a 6 weeks old baby (@ end of April 2009) doesn't help.

Apologies in advance.

22 April 2009

FT817 keypad - April 2009 update

I have added support for a status LED (green), that is ON when the keypad is in the main menu/idle. For single key press functions (such as A/B), the LED is always ON, while it stays OFF for those sequences requiring several inputs until data is sent to the radio (like direct frequency dial).
The LED is now shown on the updated schematic diagram, but its use is optional. It is not included in the bag-of-parts I am offering from time to time. I will soon release an updated free firmware that supports the status LED.

I have also implemented and tested few more functions: A=B, AGC control, PBT on/off, BK on/off, FaST tuning on/off, Split on/off, RIT on/off, Lock. The latter three should also work on FT-857/FT-897.

Hopefully soon I will be able to certify "common" Yaesu functions on FT-817, FT-857 and FT-897, so to produce a cross-radio firmware.

17 April 2009

First attempts at AO-51

I had wanted to check how easy are today HAM sats for a long time, until I decided to give them a go few days ago. AO-51 looked like a good candidate, especially now that with FT-817 I can receive UHF with a simple setup.

I prepared as follows:
  • calculated next passes on the AMSAT website according to my location,
  • picked a comfortable pass, that would fly high over my head (strangely enough, at the time I'm driving to the office!)
  • prepared a 1/4 wave vertical antenna for the magmount car base
  • located a clear spot to park
And.... right on time the AO-51 downlink signal started filling my car, even just above the horizon. It was audible for the whole pass, altough did not move the S-meter (on my non resonant antenna).

For another pass few days later I had assembled a Moxon directional antenna (two elements, folded), and tried again. While it did improve the strenght, sitting on a concrete floor created a lot of reflections and I could not follow AO-51 in its flight over my head. It was strongest when beaming to the ground! But the antenna works as expected, if pointing some ground-based signals.

Anyway, a short youtube video with audio should show you how easy AO-51 is.

On the second attempt I actually received another "bird" sending CW telemetry on the same frequency (435.3 MHz +/- doppler), but I was unable to discover who it was, yet.

07 April 2009

WSPR: Beginner's Luck?

I had to confirm my MP3 WSPR assumptions with an on-the-air test. With the family permission I erected the antenna (base loaded horizontal monopole on the balcony), plugged the MP3 pen to the FT-817 and pressed the "Play" button at the +/- correct moment. No GPS or any real-time clock sync method was involved.

Output power was in the 0.5W ballpark, perhaps less since I was careful not to overdrive the FT817 SSB circuitry (50% ALC). FT817 uses ALC to control output power, so I need to measure it (another day, please).

On the wsprnet.org website, where WSPR spots are uploaded in real time by some kind listeners, my call appeared at 4 macro-distances: 8, 1000, 2000 and 19000 km away. 19000 km means New Zealand, The Antipodes from here.

What's Next? Either setup a WSPR Moon receiver or build an independent DSB/SSB transmitter.

One thing to mention. In this experiment I ran a 100% TX and 0% RX. I transmitted for 2 hours without breaks, except for few seconds between each sequence. This can be relaxed adding 2 minutes (02'00.00") of silence in the WSPR audio file.

Call Frequency
Drift Grid dBm
by loc km

IK1ZYW 10.140117 -18 0 JN35tc +27 0.501 OH3QN KP20tx 2121 1318

IK1ZYW 10.140117 -21 0 JN35tc +27 0.501 M0DUO IO91kw 995 618

IK1ZYW 10.140130 -15 1 JN35tc +27 0.501 IK1JNS JN35sb 8 5

IK1ZYW 10.140127 -19 0 JN35tc +27 0.501 EB1APK IN73bg 1094 680

IK1ZYW 10.140168 -26 -2 JN35tc +27 0.501 ZL3IN RE66hk 18812 11689

IK1ZYW 10.140131 -24 0 JN35tc +27 0.501 G4KYA IO93ln 1129 702

06 April 2009


Stimulated by a post on the soldersmoke blog and a direct email from Bill N2CQR about simple transmitters for WSPR, I have done some real-world tests.

My idea of a simple WSPR transmitter does not include a computer to send WSPR itself, but rather use a pre-recorded sound and play it endlessy with a MP3 pen. (But record it at the highest WAVE rate your player can reproduce, ie 44100 Hz 16 bit.)

First of all, a WSPR transmission lasts 1 minute 50+ seconds and starts at the 00 second of each even minute (x:00:00, x:02:00, x:04:00, ...). I have observed this by simply listening to WSPR program in TX-only mode.

So I need a 2 minutes long file containing my WSPR message. Problem: does my mp3 player insert a gap between the end and the begin of a file played in loop?

To find out, I recorded a single tone of 5 seconds, put it in the player and played back to the computer for a few cycles. On the computer I recorded it and then used an audio editing program to analyse it. Of course the length of the test tone is non relevant to this test, just make it long enough to be able to see it on the screen. As a result, my player introduces about 660ms (0.6") between each file. Thus the total length of my WSPR pre-recorded message has to be 2 minutes minus 0.6 seconds long.

After a short session on the wave editor program, I loaded the file in my mp3 pen, wired it to the PC soundcard and fired up WSPR in RX mode. In order to take into account human errors and reaction times, I added 1" worth of silence before the WSPR message begins. So, watching the WSPR screen and the advancing clock, I press the Play button one second before the reception begins (hh:oddminute:59).
Sit back and relax (work). It takes few runs to determine how good you were in measuring the delay. After 10 runs, 20 minutes, my WSPR looked like this one on the left (first picture).
The interesting column is DT, that shows how much "off sync" the signal is with respect to the machine clock. A DT value of 1 means your WSPR signal is 1 second late. Mine started 0.9" late and decreased constantly of a 0.1 factor each 2 minutes.

This means my WAVE file + mp3 pen delay was 0.1" too short. For curiosity I left it running for few hours until it got to -2.3 (seconds) and WSPR stopped decoding. At this point probably my WSPR signal is starting too early and WSPR doesn't catch it anymore.
Back to the audio editing I added 100ms of delay and I am watching the result while typing. Now I get an increase of 0.1" every 3-4 runs (5.0, 5.0, 5.0; 5.1, 5.1, 5.1; ...), so now I'm a bit too fast. But wait, it also decreases... I might be there!

If not, with 2-3 more iterations I should be able to get a correctly timed file.

There's another way to achieve more accuracy: generate a looooong recording, such as 1 hour or so, by concatenating many 2'00.0" sections. Your mp3 player loop delay will then occur only once in a hour, allowing for a much longer unattended operation.

One more info: for these off-the-air tests and measurements you do not need a properly GPS/WWL-locked synced machine clock. So feel free to experiment!

Now I need a simple WSPR TX, but I might try this out on the air tonight. I have it ready with 27dBm, 0.5W, my FT-817 minimum setting. I'm getting excited.

01 April 2009

Distributing 12V in the shack

All my RTX and accessories work at 12V. Since I have only one high-current PSU, I had to find a solution to distribute power amongst devices.

After asking on a forum, I did what follows.

I found a 10/16A multiple socket outlet laying around. Italian AC socket outlet has three inline holes and the 16A slot fits smoothly a banana socket. Some modification was needed, but the annoying mechanical part was already done.

After disassembling the plastic case I analyzed what was inside. On the cover there was the safety mechanism that prevents someone from inserting only one pin into the socket. It is made of the blue things and spring you see in the picture above. They come off easily. Then the surprise: current is distributed with these "rails" and the connection to the plug

Since banana plugs come with two bolts, I used the first to secure the banana to the top cover, and the second for electrical contact to the rail, as visible here:

Then I soldered all connections for a longer life without need for servicing. I needed the 30W iron and a bit of patience, but it was easy. Just be careful not to overheat and melt the plastic structure. Also the supply wire <-> rail connection has been soldered.

Now I have got 4x 12V sockets just behind the PSU for my radioes.

Apparently only Italian AC accessories are so easy to adapt for this use. Usually the cheapest model adapts best. In fact I had bought a new one for few €, but chose to sacrifice this one.

31 March 2009

Lazy battery pack, an update

Following the previous post, I have done some measurements.

First of all, the DC cable to FT817 does not show unusual impedance. Not the culprit.

Then, since my analog voltage meter is out of service, I have tried a different approach: build a simple XTAL oscillator, supply it with the AA cell and listen to frequency change at different AA cell loads.

Being the human ear faster than any analog instrument, I would be able to detect quick voltage changes.

First doubt: would a standard Colpitts 2N2222A XTAL oscillator work at 1.2V? Yes, it does! As biasing resistors I used 1k5 on the emitter to ground and 10k Vcc to base. Capacitive network in the ballpark of 50-100pF each for a 14 MHz XTAL. Cool! I have just built a XTAL tester that runs from 1.2V up to ... to... 15V and more!

Second doubt: does frequency really change with Vcc variations? And how much? Well, yes, it does! I have not done precise measurements yet, and YMMV, but dropping Vcc from 1.2V to 0.8V the 14 MHz beat on my HF receiver moves 1kHz or so. What?! It still oscillates down to 0.8V! [insert and happy face here]

The resulting circuit has, on one side of the AA cell the oscillator. On the other side I put a selectable resistive load through a normally open pushbutton. The junkbox provided one 1.2ohm and one 0.47ohm 2W resistors, enough for a simple load.

I also hooked up the DVM, and measured across the AA cell (rounded):
  • no load: 1.3V
  • 1.2R load: 1.1V
  • 0.47R load: 0.8V
The beat on the HF receiver confirmed a constant voltage.

With some Ohm's law you can work out that each of these 8 cells has developed an internal series resistance of ca. 0.3ohm. Since my battery pack has 8 cells in series, the pack has an equivalent series resistance of 8 times 0.3 = 2.4ohm.
The FT817 at 5W keydown draws some 2A ... V = RI ... 2.4*2 = 4.8V of drop within the battery pack: no wonder the radio shuts down!

I did a recharge and the situation improved a little, but the pack still does not sustain FT817@5W.

I tried different AA NiMH cells and they do show a lower resistance/lower voltage drop. Strange enough I did not use or abuse that pack. Nevermind, I have learnt few things (highlighted above).

26 March 2009

Strange battery pack behavior

I had built two 9.6V circa 2500mAh external packs for FT-817. One, the older, started misbehaving.

Once charged it shows the usual 9.6+ V. If I connect the FT-817 to it, the displayed voltage is 9.6V rather than 10+V as before. If I hit the morse key the radio shuts down, except for 0.5W output power setting.

I need to check the power cord resistance, because I notice a 0.4V drop on the displayed voltage even with an external 20A PSU.

Then I suspect one or more AA cell gone bad. Now, how do I test them? I am thinking of a resistive load and voltmeter. At 5W keydown the FT817 draws 2.5A or so, that's about 0.5 ohm/3W resistor (testing once 1.2V cell at a time). I might start with a lighter 1.2A load, with a 1 ohm/1W surplus resistor. Resistors with a higher power rating are obviously fine. Let's see what I have in the junk box or recycle bin... Any better idea?

12 March 2009

The shack, storming

Taken from the model of group development ("Forming – Storming – Norming – Performing", see wikipedia), I'd say my shack evolution is now in the storming stage.

I bought a swedish designed 150x75 cm desk with extensible legs and above it a 120x28 cm shelf.

On the shelf I will install all radio-related equipment, such as RTX and power supplies. The desktop must be as clear as possible for morse key, logbook, notebook (if any) and ongoing electronic projects (on the left hand side).

The desktop will be completed towards the left wall with an additional ca. 50cm held in place with a chest of drawers: the total workspace in my laboratorio (listen to SolderSmoke #102) will be 200x75 cm.

10 March 2009

Can you see it?

This morning I forgot to collapse my 30m balcony antenna. So I took a picture from ground level: can you see where it is?

If you read this after having worked me on 30m CW in 2009, this is the antenna I used in that QSO. I was QRP too.

09 March 2009

Design ideas for a QRSS/WSPR 30m TX/RTX

The presence of a strong local QRSS 30m beacon nulls out my chances of successful DX in that portion of the band. So to enjoy these narrowband techniques, including WSPR, I started thinking of a homebrew transmitter.

WSPR support requires:
  • SSB-like modulation
  • linear RF amplification
  • stability
but the design is simplified by the fact that:
  • output sits in max 300 Hz (threehundred hertz)
  • no need for >0.5 W for satisfactory results
Given the above, combined with the fact that I have a 40.5504 MHz canned oscillator (10.1375 MHz * 4), I imagined three solution as depicted in the following picture:

Option 1 should be an SDR transmitter. Not much different in the TX chain from a simpler NE602 Gilbert cell mixer, but has an intrinsic bidirectionality that allows building a transceiver without duplicating stuff. The single XTAL filter removes the unwanted sideband (both on option 1 and 3).
Option 2 should generate an USB signal but requires a I+Q WSPR signal, that should be possible to produce software-wise.

Ah, one more thing: driving a QRPp transmitter with a QRO computer is complete nonsense. I would record WSJT signal in a WAVe file and send it to the TX with a simple mp3 player.

A good Monday morning on 30m

Before retracting the antenna in >50 mph winds (and going to work), this morning I tried some calls on 30m. Managed 3 contacts, including one 2xQRP: me 5W, RA3 with 1W.

I do not complain about dead HF bands. HI.

05 March 2009

My first WhiSPeR

Intrigued by a simple TX for WSPR mode I came across while surfing the net, I wanted to give it a try. Since at the present time I own only a 30m antenna, it was very easy.

I plugged the laptop input to the DATA socket output of my FT-817. Please note: the laptop was battery powered so to avoid ground loops. Proper radio-computer connection requires an insulated interface!

Tuned to 10138600 Hz USB and listened while the WSPR software was silently running on its own (What is it doing? I wondered...). I have a local S9 QRSS beacon just below 10140000 Hz and a lot of RTTY activity was going on (weird for a Tuesday night on a no-contest band).

On the receiver I used the variable PBT to exclude the local beacon and after few minutes the software reported:

090303 2134 16 -12 0.8 10.140133 NJ0U EN71 37 1 12556 -1
090303 2134 12 -18 -0.5 10.140146 F6BIA JN18 33 0 16341 2
090303 2134 18 -13 1.9 10.140206 W1XP FN42 37 0 1 0
090303 2134 24 -5 0.3 10.140267 F4EMV JN18 37 0 1 0
090303 2140 11 -22 0.3 10.140167 N9KCQ EN62 37 0 4180 0
090303 2140 19 -14 1.0 10.140193 F4DTL JN18 40 0 1 0
090303 2140 21 -8 1.9 10.140203 IZ1ERR JN35 37 -1 1 0
090303 2142 21 -11 2.0 10.140206 W1XP FN42 37 0 1 0
090303 2142 23 -9 0.8 10.140245 F5WK JN18 40 0 8 0

Stations were running between 2W (33 dBm) and 10W (40 dBm). I was surprised to receive French stations, that I've never heard on 30m! They were probably backscattering over the Atlantic ocean.

Nice, technically advanced system. A bit cryptic software. I am considering to build a QRSS/WSPR TX out of commonly available parts. Either DSB with a single-XTAL filter or SSB with I/Q generation.

23 February 2009

Two new US States on 30m

Did not have much energy and time this weekend for the radio, but a late Sunday night session brought in Vermont and Tennessee. The latter had a KG4 callsign, which I initially located in Guantanamo Bay. Never mind.

I was pretty tired and my CW copying skills were down to the bottom. I remembered what Hans UPL wrote me when my first child was born: sleep deprivation equals lousy CW op.

I need to build an interface to a tape recorder for my FT-817 so I can record contacts and enjoy them afterwards.

In the meantime I have drilled the shack wall to let the coax in. Antenna is still the horizontal base loaded monopole.

16 February 2009

30m update

Two new countries on my 2009 30m CW QRP challenge this weekend. The band was incredibly open on Saturday night, with many stations chasing K5 DX-pedition not minding a normal QSO. Was not so lucky on Sunday night nor Monday morning.

Statistics so far: 23 DXCC entries, 4 continents.

CU next weekend on 30m!

11 February 2009

Replacing your car radio

The cheap radio I got with an used car broke. Actually a small hook holding the detachable front panel broke, so it became useless. Not a bad news since the FM receiver was extremely poor, it played only original CDs and had a PTO tuning mechanism begging for inspection (see previous posts).
I had kept aside an old MW/FM/cassette device from 90's, that is now approximately 14 years old. It had a very good receiver, so it was time to put it back into service!

First thing to know about car radios: they have a standard outer size. So, even if they probably have different hooking mechanism to the supporting frame, they fit interchangeably. I also discovered that mine was only inserted into an existing frame, and the radio body could be pulled out with a simple movement.

Connections were worrying me. Almost two decades had passed, both for car audio industry and car manufacturers. Moreover the two cars were of different makers (Rover vs FIAT).

The antenna connector is the same. I don't know the name of that sort of plug, but I was happy with it.

Rear panel connections looked very similar indeed! Good news: those connectors are standardized, ISO 10487! Moreover both devices carried a label showing cables and their functions, so I could match them side by side and make sure no rewiring was needed.

Newer device had only A and B parts (powering and loudspeakers respectively), while older had also C. Since "C" connector is for extensions, not used in my case.

So I just plugged the antenna and the ISO connector ... et voilà ... the job was done while waiting for a couple of semaphores to turn green.

You may try this at home only if you understand the risks of playing around high capacity batteries. Take your time to make sure both connections are wired exactly the same!

I am now enjoying medium wave reception in a small city car, whose emissions render unpleasant the band:
  • below 1000 kHz, with ignition noise on weak signals
  • during rain with windscreen wiper motors noise
  • in Summer with A/C pump noise
Have fun.

09 February 2009

Crossing the Atlantic, QRP

On Saturday Feb 7th at night I got a 559 report from Maryland, USA. This is the first transatlantic QRP QSO on my homebrew balcony antenna. 30m CW, of course. TU Bill, good ears!

On Sunday night I worked Russia and Ukraine, with good signals. I was surprised to find the band so crowded after two weeks of QRT. 2xQRP was possible too.

03 February 2009

FT817 keypad - PTT for the lazy and Timed Tuning

While developing a custom firmware for the keypad, I came up with three more possible functions.

The first is a review of the Quick Tune. Rather than sending a carrier for 5 seconds, the operator controls the duration. One key press sets the radio in FM mode and TX, then another key press returns your trusty Yaesu back to the original mode, in RX. This allows to have shorter and longer tuning times. Let's call it Manual Tune.

In between this new function and the original 5 seconds Quick Tune, lies Timed Tuning. 15 levels of delay are preset, so you can chose whether to tune for 1 second, 2s, 5s ... up to 15 seconds. It requires two key presses.

Finally, the Lazy PTT is for heavy ragchewers , those operators that speak for minutes before listening back for comments. Press a button, your radio goes into TX. Press again and the PTT is electronically released. No timeout, so watch out! This is a good substitute to VOX operation.

These functions should work on 817, 857 and 897.

30 January 2009

Optics 1 : Electronics 0, tale of a partial failure

Here follows the report of a partial failure of an optical one-way contact over a distance of about 9 km (5.5 mi).

TX location: my parent's flat in the suburbs of Torino, NW Italy.
RX location: parking lot of Superga hill, 9km East of TX

In between us, right downhill the river Po and then 8 km of city with its heating fumes, car pollution, humid air that created the usual urban haze. Lights up to 10km were visible and the moon was shining on far away mountains.

TX equipment: 10mm hi-bri red led MCW driven at an average of 80mA
RX equipment: OPT201 followed by 488Hz bandpass mounted on a 90mm telescope

On the RX side we also had an EEE netbook running Argo for QRSS work.

Aligning the RX was tricky. Street lights helped to identify the area but not the actual spot. I used a pair of binoculars and cellphone with earphone to talk to the TX site (no HAM there!). No high power lamps on TX side. Then an idea: TX site is right under the landing path to our airport, and an airplane was approaching. When it was right on top of the building we got a "now!" signal.

After was just a matter of aiming the telescope and search for the blinking LED. It was sending 6 dashes, pause, cycle in slow MCW morse. Car stop lights traveling around were catching out attention all over.

Simone, the optics owner and expert, could spot the TX in a couple of minutes. Hooray! In the telescope the 10mm LED was clearly visible but as an average star would look at the naked eye! Buried in yellow street lights and reflections.

We mounted the receiver, adjusted beaming, ..., but nothing. Not even the 50 Hz hum was audible. We replaced earphones with the computer DSP software but nothing. Sometimes 50 Hz & friends were visible in the normal scroll speed, but no 488 Hz line.

Now I've got to work on improvements. I need a larger and/or more powerful source. Those 50dB over background noise we had over the 200m path were not enough for this DX. I will add more LEDs, and maybe put them in the focus of a beam expander (Fresnel lens or parabolic mirror).
I will build an aiming system for the TX, even if it has a rather broad beam.

I will build a k3pgp receiver. I have 5x BPW34 detectors. I'll probably follow Yves's circuit. Any idea for a 2N2482 replacement?

We will wait for a windy day to repeat the experiment.

26 January 2009

PTO, taking apart

Sorry I kept you waiting for further pictures of the PTO. This is it, removed from the FM 88-108 car receiver.

A small piston drives three cores in and out inductors. There are two adjustments. One marked "IF", the green can. The second looks like a trimcap, marked "OSC".

I am slowly digging my way to the circuit behind PT inductors. Then I should be able to draw a circuit diagram.

Heavier paddle

I do not own a professionally made morse paddle. Or IAMBIC key, if you prefer to call it that way.

I have used an ultimate low-cost ultra-portable paddle for all my A1A (CW) contacts, but it was also ultra-light. I had to use boths hands: one for keying and one to keep the paddle still.

It is a fine compromise when sitting on a mountaintop, but not in the shack. I asked around and those fine looking paddles weight 1kg (2.2 pounds) or more. Heaviest materials for a proper base are: platinum, gold, tungsten... marbles. They all weight more than 2 kg per cubical dm.

I excluded those noble metals and opted for a scrap piece of marble from the local reworking plant. I got three pieces of what looks like granite for a total of 2.7kg (approx 0,7 + 1 + 1 kg).

Before drilling I wanted to try the concept. Here's the result:

"JFK" in SP3 land was the first contact. Then few more rolled in, for some finally relaxing 2xQRP contacts.

Now, a new problem: how do I drill this piece of stone?

More 30m QRP adventures

On Saturday, 2009-01-24, 30m were wide open in my shack. I had troubles finding a clear spot to place my CQs: up to 10130 kHz I could hear some operators!

I could manage 6 contacts, our of which 3 were 2xQRP and two of these with GQRP members.

I was testing the new base on my freshly homebrewed paddle. So this is how the "shack" looked like...

If you have IK1ZYW on your log in early 2009, then this is probably where your signal has landed to. The balcony antenna was shows few posts back.

I wonder what the OP understood when I announced "NOW QRT FOR XYL". I had my daughter calling to play with her.

23 January 2009

21st Century PTO

I was quite puzzled when I bought a used 2005 car in 2007 and it came with a peculiar el-cheapo radio. It was an Audiola SCD-857N for which there's no mention on the Web, with the following specs:
  • FM broadcast band only, very insensitive
  • analog-like tuning (yes, a knob!) but digital frequency display
  • obviously no memories
  • CD player for original media only, not even a CD-R
At the time being, January 2009, Audiola/Majestic still sell devices with similar receiver specifications in the Italian market at 50 euro entry level price tag.

You cannot imagine my engineer's happiness when the front panel hook broke and I had to replace the whole device: I could finally peek into the tuning mechanism! The replacement is an old FM/MW/tape Daewoo car radio that I kept aside 9 years ago because of its good receiver performance (so at least 14 y.o. device). Tape vs original CDs doesn't make much difference to my listening comfort! The replacement process will be documented in another post.

The Audiola radio was built in 2004 according to its outer labels. The CD player module is stamped 12/2003. Inside I found two large pieces of thin cardboard as insulators between boards. 3 ICs are SMT, the rest are through hole R/C/L. But the tuning thing...

there you see it, at the rightmost side of the chassis. Here's a zoom view:

First thing, the black disk. it is a sort of clutch that transmits rotation from the knob to the PTO. It is needed because PTO axis and knob axis are not aligned. Cool.
Inside the metallic box there are 6 cylinders, of which only two are used, and a plastic plate pushes inside them a metallic rod. Behind them there is a shielded circuit that I haven't opened yet. It has 6 wires plus ground, a couple of holes for adjustment (there's an IF-can). One line comes from the antenna plug and another goes near the display driver chip (frequency counter?). Other 4 lines (grey wires) land nearby a couple of ceramic filters.

I have been able to remove the whole block, but not taken a picture.

What is behind the variable L? A passive circuit? Active? Could I reuse this input stage for 2m or 4m? Has anyone played with similar things?

In any case I was surprised to find such an arrangment in 21st century instead of a mechanically simpler varicap or a PLL.