[Premium-Rx] The 'Ideal' Logwire

[Carcia, Frank A. HS]

    I would use a protected gate FET as a source follower positioned at the
antenna driving the coax. The problem
    with broad band transformers is the swing in reactance over frequency. A
FET gate as an antenna termination
    would have a minimal effect over frequency. Then there is the issue of
protection.  The only way to reduce the effect
    of reactance swing is to load the antenna which also reduces the signal
level. The FET gate will require some
    type of load resistor to bleed off any static but the value could be
high compared to the typical 600 ohm 
    termination. You might also consider grounding the far end of the
antenna but a smart guy with a computer
    can tell you the difference.                fc 

-----Original Message-----
From: NewRadioChap at aol.com [mailto:NewRadioChap at aol.com]
Sent: Monday, January 06, 2003 11:32 AM
To: premium-rx at ml.skirrow.org
Subject: [Premium-Rx] The 'Ideal' Logwire


Does anyone know if there is an 'equivalent' circuit (or lab set-up) that
will simulate a typical logwire (single-ended) antenna working into a co-ax?
I don't just mean the theory - I am looking for practical work. 
I have been doing experiments and research on broadband balun designs and
construction - particularly VLF and HF (approx 10KHz to 10MHz) to optimise
my receive capability using a variety of longwires from 20ft to 200ft. I've
found that most commercially made broadband balun transformers for receive
do not appear to work very well - if at all - and have no benefit. My
homebuilt ones don't fair any better. When frequency swept, all exhibit
distinct bandwidth/resonant peculiarities. In fact, by incorrectly
connecting certain types of balun, I get a voltage boost (gain) at LF, with
high loses at HF! This is confirmed on the antenna sweep. There must a pile
of work previously carried out on this that someone can point me to, I'd
much appreciate it. If I can find a simulation, it will save me putting life
at risk trying to do measurements up a 40ft tree, and instead do them
indoors! Every dB counts.... 




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