Jerry,
Thanks for the comments. I agree that my concern is what SWR the finals on
the Pegasus are actually seeing. Now that I have the PT-11 removed from the
RIG, I plan on rigging it up so that it can be operated outside the radio.
Then I can use it to match my SWR loads and then stick the MFJ 259B on the
rig side and see what it shows for an SWR.
Mark
----- 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 18:19 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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