500kHz ATU

Spent half the afternoon going around in circles trying to measure the antenna current since I rebuilt my tiny ATU with a few more taps on the ferrite rod. For reasons I don't understand it was all over the place with my multimeter connected by about 50cms of wire. Instead I built the current meter around a toroid and a small 50uA meter mounted in the ATU and can now repeatably measure the antenna current which is 50mA. With a 5m effective height this is still way below 1mW ERP.

AA1TJ's Voice Powered DSB TX (El Silbo)

Mike has done it again - a superb piece of QRP creativity. This is from his email today:

"AA1MY and W1PID met with me on 3686kHz this afternoon. I was operating a new, DSB version of my "El Silbo," voice-powered transmitter. Both Seab and Jim successfully copied my/their calls and signal reports. Jim commented later that I would have been hard pressed to pick a worse day for the attempt. The propagation was producing severe QSB fading and the QRN was all over the place (peaking at S-7 to S-9 at times). I came away nearly dumbfounded that these two operators could pull enough of my 5mW DSB signal out of the mess, at distances of 100 and 67miles, to complete the QSOs."

Antenna measurements at 500kHz

Matching my antenna at 500kHz has been a bit hit and miss: my technique, if you can call it that, has been to match the antenna "by ear" on RX, adjusting taps on the ferrite rod ATU inductor, to give me the best S-meter reading on the intermod product on 504kHz. Then, with a 3dB pad between the PA and ATU, carefully tweek the tap settings on the ATU for maximum antenna current measured using a toroid current transformer. The 3dB pad is to prevent damage to the PA during the adjustment process. Up to now this has been OK, but I could really do with a better way of measuring the antenna parameters. I'd really like to get an antenna analyser, but cannot justify the expense. I need to check out some other simple, low cost, techniques.

14 stations hearing me on 500kHz WSPR

With a report overnight from G4KPX, I've now been logged by a total of 14 different stations on 500kHz WSPR. 13 are listed here plus G3YMC's report via the LF reflector. There is still room for further, not complex, ERP improvements which should help a few more people detect my very QRP signal. At the moment I have no plans to change my small antenna, just the grounding and ATU.

Another new reporter on 500kHz

Eddie, G3ZJO, has managed to copy my 500kHz WSPR beacon tonight. He is now the 13th station to hear me on the band. No great DX at 79kms, but pleased to be heard by someone else.

6m WSPRing and aeroplanes

Just been active on 6m WSPR this morning running 5W to the vertical colinear. The only person to report me, several times, so far has been G3ZJO who is 79kms to the west of me. What is most interesting are the number of multipath 6m signals seen on the WSPR waterfall with large amounts of Doppler shifts. G3ZJO has been analysing these are has made predictions about the aeroplane flight paths which would result in such traces. Here is the WSPR screen when receiving G3ZJO through an number of such multipath and Doppler shifted traces.

Simple beacon keyer IC: the K-ID2

Looking around for a simple beacon keyer to use with a QRSS beacon, I discovered the ICs sold for $6 (available via Paypal) from K1EL. This 8 pin IC looks ideal as it allows a variety of pre-programmed messages to be selected and sent at predetermined keying speeds.

See http://k1el.tripod.com/KID.html . At $6 each you can hardly go wrong with this. I shall be ordering a few shortly.

Another new country on 500kHz WSPR

My 500kHz WSPR beacon has now been heard in a fourth country: a -26dB S/N report from F5WK who is in the Paris area, a distance of 436kms away to the south. The beacon has now been reported by 11 different stations in four countries so far.

Lambda diode circuits

Mike Rainey AA1TJ has some good tunnel diode ideas on his pages but these devices are hard to find these days. Instead one can create a negative resistance device called a Lambda diode with a couple of FETs or an FET and a transistor. See for example the pages of Ramon Vargas Patron at http://www.zen22142.zen.co.uk/Theory/neg_resistance/negres.htm where he has examples of oscillators and regenerative receivers using Lambda diodes.

500kHz WSPR - a summary so far

So far, spots have now been received from 10 unique reporters (9 via the WSPR database + G3YMC's report using WSJT7 not shown here) in 3 countries and 7 grid squares.

If I could summarise what this tells me it is:

(a) WSPR works very well at 500kHz allowing weak QRPp signals to be detected.
(b) Very low power (ERP <0.3mW) and electrically tiny antennas do work on 500kHz if weak signal modes are used.
(c) 136kHz is worth a go next, even with the poor antenna and very low ERP.