31 December 2012

IFR, Knob evolution

2012 Xmas season has taken me back to the IFRK code, so that transverter functions would be finally included, paving the way to a long-awaited public release. Curiously, after almost 3 months without looking at the source code, I was able to identify a simple way to support the transverter math.

The current IFRK state-of-the-art is:
  • frequency computed down to 10 Hz resolution, like the FT8x7 display
  • transverter LO 10 Hz precision
  • maximum shown output frequency is above 21.4 GHz
  • tuning knob supported!
  • tuning knob has 11 steps and "fast" 10x mode
  • direct dial; in transverter mode, only kHz digits can be inserted (1296.xyz.000)
  • LO value <> memory location mapping
  • FT817 proprietary functions for power level control and A/B/C repeat on IFRK display
In order to summarize current key mappings I have compiled a table with key functions (opens in new window).

Besides some cosmetics on the display and a thorough testing, I am planning to output in binary form the LO position and/or the band selected (2 bits each). These last features would control unused pins on the ATmega168 chip, so there will be no impact on existing IFR(K) circuits.

HNY 2013!

18 December 2012

Beach40 - oscillator waveforms

The Beach40 is a simple QRP DSB transceiver for 40m, designed by Peter VK3YE who released 4 youtube videos about it. In the first video Peter draws the schematic diagram, which has then been re-drawn in electronic form and shared through the Minimalist_QRP_Transceivers Yahoo group.

It is a simple circuit, whose development can be monitored with the 100 MHz equipment of my shack/lab (oscilloscope, frequency counter). So I dediced to give it a try.

After I built the oscillator, buffer and diode-ring mixer I checked waveforms on two "test points" as identified on this modified schematic diagram:

On TP1 the waveform is almost a sinewave. The small knee close to the top occurs both with a ceramic resonator and a quartz. It also gets worse when the resonator is pulled upwards: what is causing it? How to fix it?
Probe was 10x, so 2V/div, AC coupling

Then I measured voltage on TP2, with diode ring mixer installed but without the output transformer; the effect of diodes is evident:

Probe was 10x, so 2V/div, AC coupling

And finally a glimpse at my ugly Manhattan style (probe on TP1):

17 December 2012

ADS-B with RTLSDR devices

The team behind SDR# application has released a lightweight receiver software for 1090 MHz ADS-B signals that uses an RTLSDR device right away. The ouput in AVR-like format (whatever that means), available over a TCP/IP connection, can be used by most common airplane tracking software.

From my shack and using a simple vertically polarized dipole sticked against the window I could receive pings from airplanes as far as 140 km.

I also tried a properly cut biquad antenna without reflector (which is bidirectional) but did not notice big improvement over the dipole. Since the whole system is 100% digital, I miss the analogue feedback that helps identifying signal strength, not counting that transmitters move continously ... and fast!

I will not go much further into this monitoring activity, but it was interesting to notice how little security is built around airborne airplane position!

12 December 2012

CAT Bluetooth for FT-890 and FT-840

I have been asked if the CAT Bluetooth dongle for FT-8x7 could work with an FT-890 too in this configuration:
  • one dongle owned
  • either FT817/FT857/FT897 or FT890 active at once
  • one computer active at once
In other words: you move the bluetooth dongle from one radio to the other, depending on which one you want to use.

BT dongle and Y-adapter for FT-890
FT-890 has serial data on the CAT port and voltage supply on BAND DATA and TUNER rear ports. So, it turns out that it is possible, with a relatively simple adapter, to swap the bluetooth dongle between these transceivers. One requirement is that both CAT port and BAND DATA or TUNER sockets are available. Alternatively the voltage supply can be derived right at the FT-890 PSU.

Another requirement is that CAT rate on both 8x7 and 890 is set to 4800 baud since FT-890 does not offer other choices.

Incidentally the FT-840 has the same connectors of FT-890, so swapping and/or using a CAT bluetooth dongle is possible too.

Last but not least, it is possible to build a CAT-to-Bluetooth adapter natively for FT-890/FT-840 which takes DC power supply either from one of those ports or the 13.8V PSU. It can even be "dongle shaped".

10 December 2012

Two beacons in one shot

I should consider myself lucky since I have a local 23 cm beacon to test my homemade biquad antenna. While aiming it, trying to discern reflections from the actual line-of-sight signal, the waterfall spread over 2 MHz showed another beacon, 500 kHz below the known one:

Without SDR I would not have noticed IZ1ERR/B. It was 10 dB S/N, even with the 23 cm dipole inside the house. We are in full line of sight, but it is pointing away from me (I am on his side)

I have recorded 50 seconds of baseband IQ signal with SDRSharp: if anyone wants it I will share a download link of the 404 MB file.