Dave,
I think what you are seeing is "normal." It is caused by the way SWR is
calculated in the software.
Basically, the Pegasus reports values representing forward power and
reflected power readings. The software then calculates the SWR from these
readings. There are two issues at work here.
One is that the values are reported only to the nearest whole watt. This
makes for large SWR steps when you have lower forward power. For example
with 20 watts output, 0 watts reflected is a 1:1, 1 watt reflected is 1.6:1,
2 watts reflected is 1.9. Since the reflected power can only be reported in
whole watts, you get 1.0, 1.6 or 1.9, and nothing in between.
The other issue is that the forward and reflected power may not be readings
that were taken at exactly the same time. For example, let's say that there
is an SWR of 2:1. This means that about 17% of the forward power will be
reflected.
Assume that the reflected reading was taken on a voice peak with a forward
power of 100 watts. That would be 17 watts reflected. Assume that the
forward power was taken an instant later during a lull where the the forward
power was only 25 watts. Even though the "real" SWR is 2.0:1, the program
would calculate an SWR based on 25 watts Forward, 17 watts Reflected or
about 10:1.
73,
Mark
----- Original Message -----
From: "Dave White" <dwds@trinustech.com>
To: <tentec@contesting.com>
Sent: Friday, February 13, 2004 3:59 PM
Subject: [TenTec] Pegasus Erratic SWR readings
> Has anyone noticed erratic SWR readings using SSB from the Pegasus when
the
> SWR gets about 1.5 to 1 or higher? Here's the situation:
>
> SWR less than 1.5 to 1:
> absolutely no problems at anytime.
>
> SWR above 1.5 to 1:
> readings in "tune up" are stable (ie: reads steady 1.7 to 1).
> readings during SSB peaks vary rapidly all over the map (anywhere from 1.7
> to 10 to 1)
> readings from external meter are steady and accurate
>
> No RF in the shack. Everything is well grounded. No RF in audio or
> computer lines. Tried with Ten TEC N4PY and software-- results about the
> same. Tried with 2 different antennas -- results about the same. Tried at
> several power levels -- results about the same. No internal or external
> tuners used or installed.
>
> Everything else is rock solid.
>
> Any ideas ??
>
> Thanks
>
> Dave
> VE6DRW
>
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>
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