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Re: [Amps] High SWR

To: AMPS <>
Subject: Re: [Amps] High SWR
From: David Kirkby <>
Date: Tue, 5 Jul 2011 17:14:54 +0100
List-post: <">>
On 5 July 2011 01:18, Fuqua, Bill L <> wrote:
>  There is much more to resonance that just matching capacitive and inductive 
> reactances.

Well, that is new to me.

I thought I had a decent understanding of what resonance was. I did a
degree in electrical and electronic engineering, have a masters degree
in microwaves and opto-electronics and have worked professionally in
RF design.

A couple of years ago I designed some antennas for testing the RF
properties of aircraft fuselages. I thought I knew what resonance was,
but you are telling me I don't

> It is intereting that before vacuum tubes electrical resonance was well 
> understood.

Since you believe resonance was well understood before the invention
of of the vacuum tube,  can you tell me what it was understood to be?

Since your email address is from a .edu domain, I assume you have
access to professional journals through a subscription your university
library has. You should be able to research what resonance was
understood to be prior to the invention of the vacuum tube.

I'd be interested if you can provide any professional references to
the definition being changed after the invention of the vacuum tube.
(I don't care for references to ham journals. I cringe when I see some
of the rubbish written in ham journals.)

As Roger (K8RI) has pointed out, adjusting an ATU in the shack does
not change the resonate frequency of an antenna. I don't see any
fundamental difference between an ATU and the output circuit of a
vacuum tube  amp. Both are designed to transform one impedance to

As a matter of interest, do you believe that the resonate frequency of
an antenna changes when a transceiver is switched from transmit to
receive? One might reasonably postulate that in the vast majority of
cases, the output impedance of the PA and the input impedance of the
front end are not exactly the same. In which case, according to your
understanding, the resonate frequency of the antenna must change
between transmit and receive.

BTW, for anyone who fancies a challenge, try to find the resonate
frequency of the circuit below between the points A and B.

      |  ---------R---------C---------
      |                                       |
A --|                                        |---- B
      |                                       |
      | ----------R----------L-------|

where R=Sqrt(L/C)

I expect the proportional spacing will screw it up, and I can't be
bothered to draw it in a diagram with a graphics package, so I'll

A resistor of value R is in series with a capacitor of value C
A resistor of value R is in series with an inductor of value L

Both of the above are in parallel with each other, so forming a
parallel tuned circuit.

Now what is the resonate frequency if R=Sqrt(L/C) ??

Dave G8WRB.
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