Hi Jim:
I would agree, that at HF the small amount of losses introduced with 20 feet
or so of RG 8 is pretty insignificant. I believe strongly in the double
peaked, broad band impedance match theory. As noted here previously,
Collins did specify such a double resonant impedance transformation device
for the installation of their amplifiers.
I have seen the effect of the "coaxial cable transformation device" many,
many times over many years. The need for the device is increased now by the
use of transistor finals, with power foldback control circuits. We also see
that final amplifiers which have unexplainable oscillations can be cured by
installation of this simple "device".
Can you point us to any publication which Dave Leason posted on this
subject? I would like to see the math which explains my 44 years of
practical use of this concept.
Thanks Jim,
73 and Happy DXing;
Mike Schatzberg
WB2AJI
----- Original Message -----
From: "Jim Reid" <reidj021@hawaii.rr.com>
To: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>; "ZL2AAA"
<zl2aaa@paradise.net.nz>; <amps@contesting.com>
Sent: Tuesday, October 11, 2005 4:54 PM
Subject: Re: [Amps] FL2OOOB
>
> > The first thing to try is to lengthen the coax between the amp and the
> > transceiver.
> >
> > I would recommend that the cable be at least 20 feet in length, RG 8
type
> > coax.
>
> Yes, Dave Leason wrote a piece about this coax "transformer effect"
several
> years ago. His explanation, the coax "circuit" forms a double peaked,
broad
> band impedance match. I have forgotten the math, but recall it did make
> sense. Others claimed all the coax did was introduce some loss,
> in effect "fooling" the reflections into believing the mismatch was
> not so bad. Such lossy padding is very common in microwave
> circuits. But Dave's math did show loss is not the controlling
> variable here, it is, in fact a broad band, double resonant
> impedance transformation device which solves the match problem
> Interesting stuff,
>
> Best Jim W6KPI/KH6
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