IC703 TX failure

After many years of excellent service my IC703 decided to expire on TX last night: power started to drop when running 5W on 30m then 80m (good matched load), then nothing, although I could detect a signal on the FT817, probably at mW levels.

I believe this is a common IC703 issue. Does anyone have data on how to fix this and where I get the spare parts? I believe it is either a driver or PA failure.

Incidentally Martyn Lynch quoted £45/hr plus parts and shipping to do a repair. I don't expect I'd see any change from £100.

This is the first time in 42 years of operating that I have had ANY piece of amateur gear fail, confirming that generally equipment is reliable if used carefully, so I cannot complain.

Genesis Q5 QRP kit from Australia

The Genesis Q5 is a radio transmitter kit designed for novice kit builders and QRP radio enthusiasts. With 40 parts and a professionally manufactured circuit board, the Q5 produces 1W QRP crystal controlled on the international QRP frequencies. Price: US$ 19.95 + postage. For more information visit http://www.genesisradio.com.au/Q5/ . Watch two-minute Q5 promotional "Hook 'em on" video produced by 12 years old Josh, VK2FJDX: http://www.youtube.com/watch?v=5klKvQHqqJ4

Ferrite rods as transmitting antennas?

Assuming one is running very low powers (milliwatts) and use (say) 10 ferrite rods "in parallel" for the core is there any reason why a single thick turn on a ferrite rod, suitably tuned and matched, would not make an effective transmitting loop antenna on the lower HF bands or 500kHz? As long as the core doesn't saturate I cannot think why this would not be feasible.

I have just been told about a Yahoo group for people experimenting with ferrite rods. The owner, John Popelish, experimented some time ago with stacked ferrite toroids to make a ferrite rod.

http://groups.yahoo.com/group/ferriterodantennaexperimenters/

17m WSPR

Just put the WSPR beacon on 17m and received 3 reports from W8LIW at 6105kms when using 5W to the 15m end-fed wire. Activity on 10m WSPR is very low today with no reports of signals.

Sound powered transmitters

A few people are currently experimenting with sound powered RF transmitters, generating the DC power to run a microwatt level oscillator from the human voice or morse key activation. There have been a few such ideas published. What appeals to me is a sound powered TX coupled with a crystal set RX. Such a system might get a mile or two as long as the station at the far end was running a few watts of AM or MCW. This would be the ultimate in QRPp!

There is a patent for this sort of sound powered transmitter - see United States Patent US2981833 dating from 1955 which has some schematics. This is available to view at http://www.freepatentsonline.com/2981833.pdf

DXTV - 1938 style!

There is a fascinating clip on YouTube of 405 line BBC TV being received in New York (from London) presumably by F2 or multi-hop sporadic-E propagation in 1938. This is the only example of a pre-WW2 live 405 line BBC TV transmission known to be recorded. The image shown left is of the female TV announcer. The signal comes and goes as the QSB takes the signal out of sync. Totally fascinating.

See http://www.youtube.com/watch?v=4SniB0JEDGs

Back from holiday - WSPRing soon

Just got back from 2 weeks in Greece visiting the ancient sites. Hope to get back WSPRing on 500kHz within a few days after I've caught up on things at home.

136kHz band WSPR reception

Jim M0BMU was firing up his transmitter on 137kHz today using WSPR. Managed very good reception of his 200mW ERP here at 69kms range. See screenshot - he is the yellow dashes. He was clearly audible by ear too, so a 12 wpm CW signal would have been copied well.

500kHz TX transverter schematic

This is the schematic of my 500kHz QRP TX transverter (from 28MHz). The next steps are (a) to add a couple of relays and RF sensing so that I can use it as a full RX/TX transverter and (b) changing the output stage to an FET such as an IRF510 to increase the output to 5-10W from the 700mW currently.

ERP estimates on 500kHz

Just got this letter from M0BMU who has estimated my ERP on 500kHz currently .

Dear Roger, LF Group,

It is interesting to make an estimate of what G3XBM's ERP might be...

The noise level at M0BMU during relatively quiet daytime conditions I estimate to be of the order of 3uV/m in the 2.5kHz WSPR reference bandwidth. The reported SNR gets up to about -25dB, making the signal level from G3XBM about 0.18uV/m.

ERP = (Ed)^2 / 49; with E = 0.18 x 10e-6, d = 69000m , ERP is about 3uW with only "geometric spreading" propagation losses. But there is some additional reduction in field strength due to ground wave propagation losses, perhaps 3dB with "good" ground, so the ERP would then become about 6uW. Diffraction losses due to the curvature of the earth are negligible at this distance.

Obviously, this could be +/- several dB due to various uncertainties, but should be of the right order of magnitude. Plenty of potential for improvement then!

Cheers, Jim Moritz
73 de M0BMU