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Re: Topband: (no subject)

To: "'Jacek Kubiak'" <>, <>
Subject: Re: Topband: (no subject)
From: "n4is" <>
Date: Mon, 12 May 2008 09:07:40 -0400
List-post: <">>
Hi Jacek 

I'm working on receiving antennas for 160m almost 3 years now. Here my
resume about what can go wrong with receiving your antenna. Make sure you
are listen signal coming from you RX antenna only.

1- Any resonant antenna, even a low dipole reradiates noise/signal. This is
the same principal any Yagi works, the elements are close to 1/2 wave. If it
is 5% short it works like a director, if 5% longer seems to work like a
reflector. The EWE, Flag, Pennant or the WF is NOT a resonant but the TX
antenna is. So if the RX antenna is close to ONE wave length you can expect
some interaction and the pattern of the flag or EWE will make it hear the
same signal noise the vertical/dipole resonant TX antenna. Detuning the TX
antenna during RX is a MUST.

2- Common mode noise due poor ground. Multiple antennas connected together
at one point works like a multi element vertical, and the shield together
can become resonant as well. If the ground is not a low impedance point,
common mode noise become a problem when you need to run a 20 db preamplifier
and even worst with 30 db amplifier like I'm using with my Big Waller Flag
(50ft x 20ft at 50ft high.

3- TX isolation port is the most common problem; I have a R6000 on my TX
Delta switch, this switch has a high isolation >70db. However when I forgot
the R6000 vertical connected during RX on 160m, the signal leaked from the
TX port into the RX port on my IC-7800 is enough to destroy the directivity
of my BWF. It is easy to understand why, imagine a signal s9+20 db, the port
isolation is around 60 db will reduce that s9+20 signal to S3-S4. My BWF has
30 db F/B and F/S, the noise floor is always close to S1,  S3-S4 noise makes
the F/B to drop below 10 db, destroying any improvement I can have using my
RX antenna. This problem is also easy to detect. Just disconnect your RX
antenna and try to copy signals without it, see what you can hear.
4- Antenna connector with ground disconnected. This is a common problem with
PL259 and RCA not well assembled, the shield get disconnect inside and all
the common mode noise gets inside deterioration the RX signal.

5- TX signal close to the RX preamp. This problem is common when you build a
box with TX/RX relay and a preamp inside the same box. The TX signal leaks
into the preamp input.

That list can go on and on, however the 5 points above are the most common
problems I found in the last 3 years. I hope this information helps you. 


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