SWR is determined by the feed point impedance of the antenna and the
characteristic impedance of the transmission line. The tuner can't do anything
about SWR on that line, only match (hopefully) the radio's nominal 50 ohm
impedance to whatever the conjugate impedance is at the radio end of the
transmission line.
Al
AB2ZY
________________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of Tom Osborne
<w7why@frontier.com>
Sent: Monday, April 27, 2015 12:36 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] G5RV vs 40M dipole
One thing I have noticed with the built-in tuner on my radio is that all
it does is make the radio happy.
The radio shows a 1:1 SWR, but the meter past the radio still shows a
high SWR, so if there is loss on the line, even though the radio is
happy, the loss is still there. I think the tuners just give us a false
sense of security. 73
Tom W7WHY
On 4/26/2015 9:23 PM, Fuqua, Bill L wrote:
> Not everyone knows that a tuner only protects the rig. That is the job of
> a dummy load.
> In fact the tuner matches the impedance of the antenna system to the rig and
> not only that,
> by doing so providing the antenna with a conjugate match, that is to say the
> antenna's radiation
> resistance is matched and its reactance is also matched by the equal and
> opposite reactance thus
> making the antenna system resonant. If the antenna has a radiation resistance
> of 10 Ohms and
> a capacitive reactance of 100 Ohms the antenna tuner matches it with 10 Ohms
> real resistance and
> an inductive reactance of 100 Ohms thus providing maximum energy transfer.
> While at
> the same time it provides 50 Ohms resistive load for the transmitter.
> Resonating the antenna system with a tuner is equivalent resonating the
> antenna. The only difference
> is that there may be some additional losses within the tuner and transmission
> line which are generally
> minimal at HF frequencies. Also, there is a reduction in bandwidth of the
> antenna system.
> Yes it does change the currents and voltages in the antenna. The G5RV was
> an antenna developed back
> when we had tube transmitters with a PI network output that could accommodate
> a broad range of
> impedances. It also was made to work on 5 bands.
> Just about every AM broadcast antenna system has an antenna matching
> network. It is a shame that
> they don't work.
> 73
> Bill wa4lav
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