[AMRadio] antenna tuners


Gary Schafer garyschafer at comcast.net
Fri Apr 21 12:17:48 EDT 2006



> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of kenw2dtc
> Sent: Friday, April 21, 2006 11:31 AM
> To: garyschafer at comcast.net; Discussion of AM Radio
> Subject: Re: [AMRadio] antenna tuners
> 
> Gary  K4FMX said:
> 
> > By having the meter in the shack showing a low swr or finding the
> > frequency
> > where the swr dips does not mean that is where the antenna is resonant.
> It
> > only means that is the frequency where the impedance is transformed to
> > best
> > match the transmitter. It is not necessarily the resonant frequency of
> the
> > antenna.
> 
> Would you agree that if the SWR was less than 1.5:1 at a given frequency
> that one could say that the "ANTENNA SYSTEM"  was resonant at that
> frequency?  Would you also agree that the antenna would take the same
> amount
> power, minus the feedline loss, as if the antenna were resonant?
> 
> 73,
> Ken W2DTC

You could say anything you want. You could employ an antenna tuner to an
antenna and line that by themselves have 20:1 swr at 50 ohms and tune the
tuner until there is 1:1 coming out of it. You could then say that your
"antenna system" was resonant.

If the plate tuning network on your transmitter would match that same
antenna and feed line directly without the antenna tuner, you could again
say that your "antenna system" was resonant.

It all depends on how much you want to include as your "antenna system".
As long as you don't confuse yourself as to what is really happening at the
antenna itself.

My original comments were addressing the question of whether or not the
antenna itself needed to be resonant for maximum performance. Which it does
not have to be.

Antenna resonance has nothing to do with the "amount of power that an
antenna will take". The amount of power it will take has only to do with the
construction of the antenna itself. Will it arc somewhere or melt the wire
down etc. 

The amount of power that the feed line will take (over a flat line)is
largely determined by the swr on the line. How hot it will get from the
added current as a result of the swr or if it will arc from the added
voltage due to high swr.

73
Gary  K4FMX





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