Bob Henderson 5B4AGC wrote:
> Well...........the one thing that everyone appears to be overlooking here is
> PBT. If the 2400 Hz roofing filter were to switch in at 2400 Hz DSP then
> the PBT control would not function. Instead of adjusting the position of
> the passband relative to carrier it would merely be effective as a b/w
> reduction control and Orion already has one of those.
Sinisa Hristov YT1NT wrote:
> Not true.
> It is easy to verify that PBT functions correctly
> with both filters at 2400 Hz, or any other value.
I was on a camping trip the past 3 days and was
interested to verify this when I got back today. Indeed,
Sinisa is right as usual. This has some very interesting
implications for using PBT to position your roofing filter
to minimize intermodulation products (IMD). Even with the
stock 1000 Hz filter, you can use PBT to better position
the roofing filter to reject the source of IMD products
that might be closer than +/- 500 Hz. Of course this only
works for IMD interference from one side at a time.
If you experience IMD interference, I would try the
following (in order):
1. Adjust PBT.
2. PREAMP Off.
3. ATTN 6 dB. (more if necessary)
73, Bill W4ZV
P.S. Bob, I called you with 5 watts to a vertical 1/2 wave
in a tree by our campsite after you worked K6VVA. Guess
even Orion cannot hear everything!
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