Received-SPF: neutral (gmail.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org)
Message-ID: <001101c69f68$fa306a90$6501a8c0@eagles>
From: "J. Allen" <vy1ja@northwestel.net>
To: <lowfer@lwca.org>,
	<rsgb_lf_group@blacksheep.org>,
	"Steve McDonald" <jsm@gulfislands.com>,
	"Scott Tilley" <sthed475@telus.net>
Date: Tue, 4 Jul 2006 12:54:24 -0000
MIME-Version: 1.0
Subject: LF: Antenna Tuning
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=original
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Steve, Scott, and All,

Last night, I was following a thread of another person and their problems 
with SWR detection in the presence of a nearby strong LF transmitter.  It 
did not dawn on me until this morning that the problems with the LF antenna 
tuning here relate to what looks like an even order harmonic on a system 
based on the square wave which generates high odd order harmonics, not even. 
The antenna tuning problems are much harder to get any change in the voltage 
portion of the SWR, and are more pronounced at low power used for antenna 
tuning than at higher power.

I believe that the very strong signal from the LF beacon less than a mile 
from here which operates on about 240 kHz. is effecting the voltage portion 
of the ScopeMatch readings and that this may be why the problem has been 
elusive to the point of discouragement.

Here are three ideas which I put out for feedback and suggestions.

1. During my testing, vary the frequency slightly and see if it shifts the 
voltage wave shape because of the way the two signals combine.  If it does, 
my antenna is acting as a voltage pickup.

2. Put the LPF which I built out at the antenna terminals so that it blocks 
the voltage signal from getting to the scopematch pickup.

3. Add a second FET to Steve's bulletproof antenna tuning transmitter, so 
that it produces a stronger voltage signal and masks the voltage from the 
nearby antenna.

What do you think about these ideas?  Are there any other ideas you can 
think of which will make testing more successful?  Is there a different kind 
of SWR circuit which works better in the presence of a strong signal?  I 
wonder if any of my friends in EU have had similar problems and have found a 
way to beat it.

Help anyone?

JA

VY1JA.