28 July 2014

Painful discovery about Baofeng UV-82L

Few months ago I bought a Baofeng UV-82L so that I would have a 5W dual-band handheld, since the little UV-3R has been stuck in the car on a fixed frequency.

Seconds after paying it I realised Baofeng UV-82L does not have a DC socket for recharging or powering the unit: it works off the battery and it requires the charging base. Not so practical if you are often on the move, or you don't want to keep the base on the desk all the time.

That said, the transceiver works as expected. Being confined to "memory mode" (without power-cycling it) is not a big deal once local repeaters have been programmed. But yesterday I did a painful discovery. I was checking if a friend was still up on a mountain and I moved around the flat with the UV-82L in my pocket while doing other things. Then I heard a /P station calling on the VHF direct frequency for mountain op's and engaged a QSO with him. During a transmission I felt a mix of burning/biting in my hand holding the radio ... right there where battery contacts are located!

My palm, slightly salty-wet from Summer sweat, was draining current out of the Lithium battery pack. I haven't had time to double-check with a resistor and ammeter, but most probably there is no reverse-discharge protection diode into the battery pack. There is no fix.

Edit. I confirm, positive charging terminal is connected to the positive battery lead going to the radio. Same goes for ground terminal. At least in my BL-8L battery pack.

10 July 2014

Like a child on 70 MHz

The day after Italian HAMs were allowed to use 70 MHz band again for a few months in 2014, I reconnected my transverter and erected the dipole on the balcony. I tuned the band checking the local beacon with my ears and looking at the DX cluter with my eyes: the band was open.
All of a sudden I heard someone distant having a QSO. Disappeared. QSB was very fast. Then another voice, very strong, GM4JTJ, that came back to my 5W SSB balcony signal! Hooray!

I felt like 25 years ago, when as a child I worked my first DX'es on CB channels. I kept tuning, calling CQ, tuning, trying to ignore the female voice(s) calling me for dinner. But this time it wasn't my mother's voice, it was my youngest daughter's reminder that dinner was on the table.

I walked to the kitchen, explained that a unique event was going on, an event that happens 4-5 times a year and doesn't last long. When returning to the shack I got the familiar "don't complain if there won't be food left for ya", this time thrown at me by the older daughter.

It was a funny parent-child-parent role inversion.

In the following days I came up with a quick way to explain propagation. You must have seen Stargate movie to understand it: sporadic-E looks like a wormhole opening to some random part of the world.

Now waiting for another randomic wormhole...

08 July 2014

My Moxon beam for 70 MHz

I like the compact design of Moxon 2-element directional antennas, even if they are harder to build than a normal Yagi. Given the fact that 4 metres in Italy are allowed year-by-year, I do not want to invest in a large antenna, and I believe the gain of a Moxon should be enough to take advantage of sporadic-E openings.

Last year I had started building one and almost forgot. Then yesterday I had a pleasant surprise when I realised that everything was ready to erect the antenna and measure SWR! The only "problem" was how to hold the two wire ends pointing at each other.

Problem solved with two rubber bands cut open and secured to the wire with simple sticky tape!

The H-shaped frame is made of 20 mm PVC pipe screwed together with slightly modified Tee joints.

A huge storm was approaching, but wind was light so I could lift the antenna on the fiberglass telescopic pole on the balcony, measure lowest SWR at 66 MHz (1.6:1 at 70.2 MHz) and take the picture above.

Both local beacons were off-the-air, so I could test the extra gain.

Then the storm came and it offered a good opportunity to experiment with the camera: