This month Rob G3XFD reflects on two interesting letters published this month on the letters pages. One deals with 'round the World Echo' transmissions and the other a less attractive type of signal

World Echo Transmissions

• The letter from Andy Foad G0FTD (Long Delay Echo Mystery Solved?) in the Letters pages, proved to be fascinating to me.

I've not experienced the phenomenon involving radio transmissions that have obviously encircled our beautiful planet often - but when I have done I found it to be an extremely 'creepy' experience!

The only occasions I've actually heard my own transmissions after they've travelled 24,000 miles or so (38600km) around the planet - have been when G3XFD/P has been on the air. Operating from my parked car - usually on relatively low power c.w. (below 20W input) my antenna of choice was mostly the Pro-AM whip for use on 7, 14 or 18MHz.

The only times I've heard 'round the World echoes' has been when I've been using vertical polarisation. Personally, I think this is a vital factor, due to the low angle radiation from this type of antenna. To check on what antenna Andy was using I 'phoned him to confirm it. My hunch was right - he was using a vertical antenna and had a clear 'take-off' over the sea. Andy also told me the Japanese operator's voice had marked 'reverberation' effects on the audio.

The 'creepy' experience I mentioned earlier, came about some years ago when I was parked high up on the Dorset Downland, near Shaftesbury. I was calling "CQ" on 14MHz using c.w. and had the strange feeling that another station was on the same frequency, also keying "CQ", but a tiny fraction of time after me. When I stopped - the phantom keyer stopped. Then I realised - the 'phantom' signals were my own, returning after a quick orbit!

Tuning down to the International Beacon Project (IBP) frequency on 14.1MHz I listened out for any of the 18 beacons that transmit in the IBP three-minute cycle. Sure enough, up came the Californian beacon W6WX (near Son Jose), at RST599 with multiple echoes, followed by KH6WO in Honolulu in Hawaii, also S9 together with multiple echoes on its 10, second transmissions.

The echoes sounded like out-of-synchronisation 'shadow' transmitters. A weird experience! Importantly (for my theory that vertical polarisation is an essential factor) all the IBP beacon transmitters use Cushcraft vertical antennas. And, just in case there are any PW readers who don't know - during their 10 second transmission slot (every three minutes) the IBP transmitter provide its callsign at 22w.p.m., followed by four dashes. The callsign and first dash is transmitted at the 100W level, the second dash at 10W, the third at 1W and the fourth at 100mW. It's a truly wonderful system for checking to see what conditions are like at the time you're on the band. (see PW January 1999, pages 36).

Propagation on h.f. is fascinating and we've still got much to learn. And, speaking from personal experience - I think there much more of a link between prevailing weather in the troposphere and variable h.f. conditions than is acknowledged. But that's another topic!

Valved Equipment Components

Peter Hague (Letters, this month) had some interesting suggestions for making up difficult-to-get components for valve projects. Do you still build equipment using valves?
If so, are you like me and have abandoned traditional chassis - and use p.c.b. material instead? What techniques do you use?

Please write in to me at the PW offices, as I would like to hear from anyone who enjoys using valves. If you still enjoy seeing filaments glowing in your workshop - let us know you're still out there!

Rob G3XFD

• In this month's Practical Wireless

Latest news stories..

• Get our news headlines for your website • Submit your news story