[Antennas] Re: VSWR on log periodic

[Don Havlicek]

Comments inserted below:

Richard Hassell-Bennett wrote:
> 
> Subject: Re: [Antennas] VSWR on Log Periodic.
> 
> > In my opinion, the ONLY meaningful SWR measurements are AT THE
ANTENNA..
> > NOT at the shack!
> > Don - N8DE
> >
> 
> Interesting opinion..........  At resonance the SWR will be 1 to 1.

Really? ... doesn't VSW.RATIO .. depend on the impedance the antenna is
being compared to?

>  But who
> can say what the impedance will be !!!

Perhaps I assume too much .. but, I believe that VSWR measurements are
done to compare the feedpoint impedance of the antenna being measured to
the desired impedance??

> 
> Without a feedline SWR is meaningless.

I disagree!  The only important thing here is the feedline IMPEDANCE ..
not the actual feedline that is connected to the antenna.  As pointed
out by others, the combination of antenna and feedline can make a good
'match' to the 'source' [call it transmitter, amplifier, whatever],
despite a very POOR match at the antenna!

As for the 'problem' of doing measurements at the antenna .. isn't that
what we attempt to do BEFORE we haul the 'beast' up to 200+ feet in the
air?  I do ALL measurements AT THE TOP OF THE TOWER.  Sometimes this
requires 'gymnastics' ability .. reaching the feedpoint of a
multi-element yagi sometimes proves to be the equivalent to some Olympic
Sport!  But, I would rather know that the feedpoint impedance was the
desired value THERE, instead of at the end of some weird length of
feedline.  Remember, if the impedance of the antenna matches the
feedline impedance .. ANY length of feedline is OK.  [Yes, I know that
will occur ONLY at ONE frequency!].

73
Don - N8DE

> 
> Richard K0XG