Greetings TT Mavens.
Background -
I rarely work 17 meters SSB with my Omni VII. Today, I reworked my 10
meter vertical ground plane antenna into a 17 meter ground plane which
measures about 1.3:1 SWR at around 42-45 ohms both in the back yard and
inside the shack using a RigExpert AA-230 analyzer.
I also have a TenTec Centurion and a TenTec 238C and/or a Palstar
AT-auto matchbox in line, which I alternate using at my whim on other
antennas. I generally put them in bypass mode when working a resonant
dipole or vertical.
For 17 meters, I set the Centurion to the 15m Band, and set the LOAD and
TUNE controls according to the chart in the user manual, and then fine
tune for most power out with the TUNE knob.
Sidebar: This seems to be a very forgiving amp...
I can set the LOAD wide to either side of the
recommended LOAD setting and it has no apparent
effect, while the TUNE control is quite response
and it is easy to tune to highest power out with
very little movement. The Plate Meter almost
never changes no matter what I do. I have never
heard it arc or make any odd noises... he said
knocking on wood...
When I briefly transmit a CW tone barefoot on 17 m, the rig meter says
it sees 1.2 SWR, but when I put the amp in line, and run exciter power
(maybe only 2-30w) I get 2.1:1 SWR. I have not tried it on higher
power. I am sorry I don't recall what it did into my dummy load, and I
cannot test that again right now because a humongous thunder storm is
rolling in off Lake Michigan and ...well... you understand my reticence
to be operating while that is brewing in the neighborhood.
The Inevitable Questions -
* So... why does this happen?
* Is this a normal occurrence?
* Does this have anything to do with working 17m
opposed to another band? The radio usually
reports SWR close to the antenna's inherent
measurements on the other main bands like 40m
20m, 15m, and 10m. I have not tested for this
on 12m or 30m.)
* Using the auto tuner does not change this dichotomy
of SWR reports. I did not think it would, but
I tried it anyway.
So... any thoughts?
---------------------- K8JHR -------------------------
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