Re: LF: First Portable Trip

[lawrence mayhead <laurie.mayhead@googlemail.com>]

Hi Richard,
I must commend your efforts to go portable. However there seems to me to be one major problem. That is GROUND, all antennas except loops (more later) need to work against "Ground" which is not really ground as we know it since at LF the earth is pretty transparent, varies a bit, but mainly RF penetrates many feet. Think about cave radio. So we use counterpoise/radial etc. wires, but to be any good these have to be quarter wave long! ie 125meters !!! not easy when you are portable. At home the mains feed, is probably the best radial available, since it goes to all the other houses far and near. So your problem is not so much to fly a kite or balloon but to find a few hundred yards of viable fencing/old railway etc.
But Loops are different, no ground required and mebbe you could lay a horizontal loop out on the ground (its pretty transparent after all ) better still a mountain site not in East Sussex though I guess. Lots of data on LF Loops on the reflector, matching etc. 
Best of luck and will always listen for you
73 Laurie.

2009/5/23 <g0mrf@aol.com>

Hi Richard.

I've used a system similar to yours with some success.  Mine, now dismantled, is detailed at

http://www.g0mrf.com/500kAntenna.htm

It was a 10m mast with a very small 3m top section. Power in 7.5W PEP.
100km was no problem 24/7 with good conditions it made it to ON and PA.  With very good conditions it made it to the Scotish Islands at apx 800km but that was rare.

The photo shows a variometer in series with a fixed coil in series with another fixed coil which was connected to ground at the bottom end.  Despite all these turns of wire, the 50 ohm match was only a few turns up from the ground end.

Hope that helps.

David

-----Original Message-----
From: Richard Newstead <g3cwi@btconnect.com>
To: rsgb_lf_group@blacksheep.org
Sent: Sat, 23 May 2009 16:06
Subject: LF: First Portable Trip

Not a great success. Tried a 200ft inverted L with 7m vertical section fed against 3 radials each between 50 and 100ft long. The final 100ft was very low - within 1 metre of the ground. 
 
Did not succeeded in tuning aerial up in link configuration. Tried tapping the feeder at various points on the main coil but this reduced the Q dramatically and the RX and TX performance were very poor. In configurations where the RX performance was good and the Q high, there was little on no aerial current on transmit. The only configuration that gave some antenna current was nearly useless on receive. Connecting a radial to a metal fence detuned things so much that I go nowhere like that. 
 
Heard GW0HXO's beacon at reasonable strength and GW3UEP's beacon - just. Called CQ quite a few times. No takers. 
 
Band was still noisy even on relatively remote hilltop with horrible "line-timebase" type burble drifting across band. 
 
Clearly more work required to get a viable system. Tips? 
 
73 
 
Richard 
G3CWI 
 

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