500kHz TX schematic (5W)

This is the current schematic of the 500kHz TX down-converter I use for WSPR. It uses an IRF510 FET PA and generates about 5W from the PA stage, although the ERP is only around 1mW from the antenna. I am planning to add the RX converter stages and an RF sensing circuit so I can use other modes in full transceive on 500kHz. The input is my FT817 at 500mW on 28MHz which is mixed down to 500kHz in an SBL1 mixer.

G0NBD and G4FDD log me on 500kHz

My 500kHz WSPR signal has been logged by new reporters G0NBD in IO83 square (261kms) and G4FDD in IO93 square (212kms) tonight.. This now brings the total number of different stations that have heard me to 16. Not bad with <1mW ERP.

10m - CQWW SSB DX Contest

This BIG HF contest runs this weekend and is sure to make the bands sound busy. I shall be having a go with 5W SSB on 10m only and see what happens.

By 1600z Saturday I'd worked 24 stations in 16 European countries with 5W QRP SSB including C4I, P33W, 4L0A, US5D and TM1O. It is nice to hear 28.4-28.55MHz crowded with stations. Funny how "conditions" magically improve when there is a big contest! In the afternoon there was some decent DX about including LU1HF and PW5G but I did not work them.

EPAD FETs and low voltage TX

This application note shows a 32uW oscillator using EPAD FETs that works with 0.5V supply and may be useful for "harvested energy" TX circuits. The ALD110800 FETs used has also been used to power an amplifier with just a 0.2V supply.

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.