Date: Wed, 16 Jun 1999 01:31:21 -0400
From: "Dave Sergeant" <sergeantd@compuserve.com>
Subject: LF: Antennas, bandwidth, etc
To: rsgb_lf_group@blacksheep.org
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>From Dave G3YMC

<You should see my antenna in the moment. Everything that can be done 
<wrong (following the theory) was done wrong: not heigh enough, not
<sufficient ground, one top-wire is broken at the moment, between the
<loading coil and the top point, the antenna has an inclination of about
<60 degrees, most of the antenna is in the trees with leaves, and so on. 

This sounds very much like a description of my antenna!

<I haven't done much to improve it lately since I am waiting for the
<fibre-glas 
<mast to be delieverd. My estimated ERP is around 35 mW, maybe less
<in the moment. This should encorage everyone even with a small antenna
<to try Slow-CW! The distance between Mike's QTH and mine (JO52BH) 
<is 707 km! Sorry, Mike, that I could't copy you, I have trouble with local
<noise from time to time here. But thank you very much for taking the
<time and try to copy such a weak signal!

<Best 73

<Geri, DK8KW (W1KW)

Like Geri I would encourage everybody with small antennas to have a go, and
not just slow CW.  With normal CW and 35W I have worked to 468km.  Fairly
hard going at times, but even more satistying to achieve what I do.

Mike G3XDV states:
<The idea of an LF antenna being too narrow for CW is a myth, certainly
<for the very lossy tiny-fraction-of-a-wavelength antennas we use. With
<practical losses of several ohms in a loading coil and tens or even
<hundreds in the earth system, bandwidths are relatively wide.

Mike is probably right.  Unfortunately most of us see the transmit
bandwidth of the antenna as being that for which the SWR is acceptable. 
With my present loop antenna the usable bandwidth, ie that within which the
SWR is less than 2:1, is about 200Hz.  Having not yet built my remote loop
tuner this is embarrasingly narrow! However the bandwidth the receiver sees
is probably rather a lot more than this.  In any case I have a couple of
fixed tuned circuits in the receive path which limits the bandwidth to a
few kHz.

It is true to say that I can detect no slurring of the edges of dots on any
signals I copy. Any difficulty in copying weak signals is inevitably due to
noise considerations, which will always effect the dots first.  If you
listen to Finbar EI0CF, who has more dots in his callsign than most, you
may appreciate what I am saying!  (no offence Finbar!).


73s Dave G3YMC
sergeantd@compuserve.com
http://ourworld.compuserve.com/homepages/sergeantd/136.htm
(read how it is done!!)