Hi Steve,
There was a consensus of replies that the variation of display brightness, and the "key up
thump", seem to be "features" that other Omni VIs exhibit.
The variation in display brightness is a feature. Key up thump? Not in
my Omni VI.
At warm-up several heterodynes, one after the other, drift quickly through the pass band
- all of them are non-tunable. Once the rig is stable, if I'm left with a heterodyne in
the pass band it can be tuned out with PBT control. I don't mean "filtered out"
with PBT; just a few degrees rotation of the PBT control around its mid position and the
heterodyne rapidly moves in audio tone and out of the passband. If the PBT control is
more than about 5 degrees away from its central position I never hear a heterodyne at
all. I guess this must be some funny mixing product involving the15.3 MHz PBT oscillator.
A very interesting problem. Since it happens on all bands, I would guess
that the 15.3 MHz PBT oscillator is generating a spurious signal that is
getting right into the 9MHz IF, or even the 6.3 MHz IF. Come to think of
it, suppose that the 15.3 MHz PBT oscillator is mixing with the 9 MHz
BFO, and generating a signal at 6.3 MHz. Changing from USB to LSB would
move the 9 MHz BFO, and the setting of the PBT required to hear the
unwanted mix would also move. Does that happen?
So then why would your 9 MHz BFO oscillator or 15.3 MHz PBT oscillator
radiate, or conduct through undesired paths, more than most other
peoples? I would look for loose connectors and board mounting screws
around the TX Audio Board (which includes the BFO) and the Passband
Tuning Board. What about the shield covers over the optional crystal
filter access? Are the shields there, with all the screws in place?
DE N6KB
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