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Re: [TowerTalk] M2 20M5 SWR measurements

To: "'Towertalk'" <>
Subject: Re: [TowerTalk] M2 20M5 SWR measurements
From: "Jorge Diez - CX6VM" <>
Date: Sat, 31 Dec 2011 09:22:12 -0200
List-post: <">>
Hello Tony and Stan,

Thanks for the replies.

Will be next week in the station and will measure adding 23ft coax as Stan

Tony, may I put the beads in the side of the coax inside the shack? Or are
you talking about putting then in the side connected to the antenna? I use
the original M2 balun, I think this will prevent for RF on the putside of
the coax, right?

I don´t know about the K3 internal meter, but the powermaster by
Arraysolution seems to be good, at least expensive :-). No possibility to
use a bird here, I don´t know someone that have one.

Another test I will do is to measure the antenna directly to the AIM4170 and
see if any varioation when I add this 8.35 ft, 

Will send the reports next weekend

Happy New Year!!!


-----Mensaje original-----
[] En nombre de Tony Brock-Fisher
Enviado el: Sábado, 31 de Diciembre de 2011 01:55 a.m.
Para: Towertalk
Asunto: Re: [TowerTalk] M2 20M5 SWR measurements


Assuming your 8.35 foot jumper is lossless, it should not affect the SWR on
the line. The addition of transmission line changes the complex impedance,
but not the SWR. A perfect SWR meter would not show any difference with the
addition of a length of lossless transmission line. A vector impedance meter
of course would see a difference. For example, as transmission line is
added, a Smith chart would show the different points along the line as a
circle, having different real and complex impedances, but having a
consistent SWR.

So what you are seeing is changes in the reported SWR with the two meters
you have due to impedance changes. This can be for one of two (or more)

1. There is RF on the outside of the coax. Try adding several beads on the
coax and see if this makes things calm down, and gets identical readings
with and without the jumper. Many SWR meters can be affected by RF on the
outside of the line.

2. The meters are sensitive to the load impedance, and are not 'perfect' or
'ideal' SWR meters. Perhaps try a Bird meter.

All of this is not really saying anything about the antenna itself. But you
have to satisfy yourself that you are accurately measuring SWR before you
can worry about what is happening at the antenna.


-Tony, K1KP

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