Hi all, this is an interesting discussion.....I don't how pertinent this is
but I have been trying a few 'rear of envelope' calculations. Using Dave
G3YMCs figures for dynamic resistance and and assuming it increases linearly
with increasing loop periphery, I worked out the efficency of several loop
sizes. Then I calculated the efficiency of an L, which could be errected in
the same space (2 sides of the loop), assuming a ground loss of about 60
ohms. The crossover point came with a loop of about 110m by 10m, assuming
only a 10m height. I calculate that as the radiation resistance increases
rapidly with height in vertical , Mal would probably have to put up 30m by
90m loop to compare with his vertical (which I calculate at about 0.6 ohms
This is rather over-simplified as it does not allow for the reduction in
loss resistance as the L increases in length
I will put the formula into a EXCEL spread-sheet and make it available on my
web site http://www.alan.melia.btinternet.co.uk look in the useful programs
One area where the loop might help is in 'static' conditions. The loop will
receive the EM waves from lightning flashes but it should not collect the
local voltages that a vertical does.
There has been quite a bit done with QRP in Eupope and 1w to an average
aerial does not get you very far on hand keyed morse, particularly in
daytime. G6RO has used a 5 watt rig quite a lot as did Steve GW4ALG before
he left the band. Their best DX was about 300 miles with a following wind.
Geri DK8KW could also relate the experiences of the German stations who were
limited to 20w output.
Cheers de Alan G3NYK