I am selecting which of my transceivers to take to Field Day with the
choices either my Corsair II or my Omni-VI+. You would think this to be
a slam dunk decision in favor of the newer radio. However, I still have
a very bad memory from last Field Day when I took a Kenwood TS-940SAT
which had so much Phase Noise that when transmitting I wiped out the
other two club stations. I have subsequently deep six'd that
transceiver. Now not wanting a repeat of that experience I decided to
make a very simple test.... and got rather disturbing results.
Test One: Omni-VI+ to a dummy load. 14.005 MHz. Power output varying
between low and hight power. Keyed with electronic keyer. Corsair II
with unterminated receiver (basically on a shorted connector of the same
switch connecting the Omni-VI+ to the dummy load). As I tuned across
20-meters I could not hear the Omni-VI+ transmitting until I was pretty
much on the transmit frequency +- say 3 kHz. This was satisfactory.
Changing the Corsair II's XTAL filter to 1.8, 500, or 250 Hz made the
reception tighter as expected.
Test Two: Reverse the roles. With the Corsair II transmitting at even
the least output possible the Omni-VI+ presented 'keying' noise across
the entire 20-meter band with a few false signals to boot! Inserting
different first or second IF filters did little to reduce this.
Eeeaaoooouuucchhhhh! Granted the noise floor alternately raising and
lowering with the keyed Corsair was maybe an S-3 to S-4 level but having
that noise constantly present for 24 plus hours..... Hmmmmm.
To be sure that this was NOT the Corsair II's problem I turned on
another transceiver..... an Argosy with an 8-pole first IF filter. The
Argosy's response to the keyed nearby transmitter was even better than
that of the Corsair II's!! Hmmmmmm, something to be said for
single-conversion designs.
I got on the phone and talked to a tech at Ten-Tec about this. He did
NOT indicate that this was abnormal for the Omni-VI+. He did state that
the Corsair II was arguably the finest 'analog' transceiver ever
made..... still he recommended my using the Omni-VI+ as he believes it
to have a better receiver. Now this is something I have never been able
to confirm. I said what about the Omni-VI+'s susceptibility to the
nearby transmitter? Long pause..... No comment.
Next I asked him if he thought adding the INRAD roofing filter might
help. I had my doubts as the interference was felt across the entire
20-meter band! Knowing that the Omni-VI+ has a 16 KHz monolithic crystal
roofing filter already I wasn't sure how putting a tighter filter would
help. Still I am grasping at straws here.
He did say that a number of INRAD roofing filter equipped Omni-VI+
transceivers have found their way to Ten-Tec and that there was a
'noticable improvement'..... and that INRAD filters have been found to
be of very high quality.... Yada yada. Would it help with what I am
experiencing? No way to know.
So what do you think? Have you installed an INRAD roofing filter in your
Omni-VI+? Which... 2.4 or 500 Hz? And did you use your
unmodified/modified transceiver in a multi-contest environment?
Thanks for the input.
Jerry, KG6TT
--
KG6TT
Ralph Jerald "Jerry" Volpe
ARRL Member, VE
FISTS Member 12304
Solano County
CM88xg
kg6tt@arrl.net
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