[Antennas] VSWR on Log Periodic.

Sun, 28 Apr 2002 02:04:33 +0200

I have heard this statement mentioned before, that you could calculate the
SWR at the antenna from knowing the SWR at the end of the feedline and the
feedline propperties, but I have to disagree.

If you knew the impedance at the end of the feedline and the feedline
propperties you would be able to calculate the impedance of the antenna. But
that is another matter entirely.

Picture a smith chart, a given SWR say 1.6 is a circle arround Zo. Any given
feedline will move a point on this circle to another point in the smith
chart, forming another figure. All the points on this distorted circle are
possible candidates for the ipedanse of the antenna and will give wildly
different SWR's.

What makes you guy's think that there is a way to calculate 1:1 from SWR at
the feedline to the SWR at the antenna ?

Do you silently considder the load to be purely ressistive ?

Greetings from Denmark.
Jesper Wolf Jespersen
OZ8ACE

----- Original Message -----
From: "Harvey&Bessie" <[email protected]>
To: "A10382" <[email protected]>
Cc: "Antenna reflector list" <[email protected]>
Sent: Thursday, April 25, 2002 8:30 PM
Subject: Re: [Antennas] VSWR on Log Periodic.

> If the line loss is known, it a simple matter to compute the actual SWR
> (SWR at the antenna) from the reading at the transmitter. As someone has
> pointed out, Maxwell shows how to do this in his book. Why make a big
> deal of it? It is simply too inconvenient to measure it at the antenna,
> for the value one gets from that reading. Of course, in cases of high
> line loss, one sees a very favorable SWR "downstairs" even when there is
> a poor match "upstairs."
> Harvey/W4TG
>
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