Jerry,
I think you missed Mark's last post. He proved rather conclusively that the
problem
is an impedance "bump" in the internal tuner itself. With the internal
tuner removed,
he got excellent agreement.
Just think about it. With the internal tuner in bypass, there has to be
relays that are
bypassing the tuner circuit. It is almost impossible for these relays to
not present an
impedance bump, especially at the higher frerquencies. Now since the
pegasus does
not cut back power with SWR, the next experiment would be to measure power
output externally and see if the internal tuner really is hurting anything.
I suspect
it really hurts nothing.
Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@isunet.net>
To: "Mark Erbaugh" <mark@microenh.com>
Cc: "Dwayne Kincaid (LDG)" <ldg@ldgelectronics.com>; <ditsnbits@tentec.com>;
"Ken Brookner" <kenb@brookner.com>; <tentec@contesting.com>
Sent: Tuesday, January 08, 2002 11:19 PM
Subject: Re: [TenTec] Pegasus Internal Tuner
> Sometimes a SWR meter shows a match on its load side but if it couples
> tightly to the line, the SWR on its input isn't matched. That is
> probably what is making the Pegasus show higher SWR readings than the
> coupler in the tuner. In most ham style couplers, the coupling is
> greater (and thus the effect on input match) is greater the higher the
> frequency. Sometimes if you can pick a line length between the
> transmitter and the SWR bridge (standard Bird technique) that is a total
> of a half wave long including the line length of the SWR bridge you can
> minimize that effect, though that's tough with 9 HF ham bands.
>
> The big question is whether the input impedance of the tuner plus its
> swr bridge is within what the Pegasus will supply full power to or if it
> causes a power reduction from mismatch. If the Pegasus won't do full
> power through the tuner's swr bridge, its time to scrap that swr bridge
> and find one that has less of an adverse effect on the swr. E.g. one
> with smaller coupling coefficients, that may need some more DC gain to
> run the automated tuner's logic. Though the smaller signal the gets to
> the detector diodes the poorer they work without a lot of external help.
> Maybe the reflected side needs an RF amplifier before the detector to
> make up for loose coupling to the transmission line.
>
> Then maybe the swr bridge is just sloppily made and that makes it upset
> the SWR on its input.
>
> Your antenna analyzer and the Pegasus agree that the SWR bridge in the
> tuner is the culprit. It probably can be fixed.
>
> 73, Jerry, K0CQ
>
> --
> Entire content copyright Dr. Gerald N. Johnson. Reproduction by
> permission only.
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