[TenTec] More Omni VI alignment/functioning questions...

[John Clifford]

Yes, but you must use the correct trimmer caps.

The proper Omni VI BFO alignment (TX Audio Board #81597 Rev. F and earlier)
is as follows:

 - You will need an ACCURATE high-resolution frequency counter.  Using an
oscilloscope probe with "hook-on" attachment, attach the probe to resistor
closest to the BFO coax jumper socket #46 (R38) at the end of the resistor
AWAY from #46.  Attach the ground clip of the probe to the metal outer
ground sleeve of the jumper coax that is in the socket.

 - Select LSB, stay in receive mode, adjust C10 until the BFO freq is
exactly 9.000000 Mhz. (Y1)

 - Select USB, stay in receive mode, adjust C12 until the BFO freq is
exactly 9.003000 Mhz. (Y2)

 - Attach a dummy load to the rig, and turn the power all the way down.  You
do not need to transmit with any power to adjust the following modes, but
you must be in transmit mode while adjusting

 - Connect an RCA patch cord to the FSK Mark/Space jack on the back of the
rig.  You will need a way of putting a positive voltage (2.5v to 15v) on the
cord for Space, and a negative voltage (0 to -15v) for Mark.  I think a 9v
battery would be fine for this... short it against the RCA plug on the other
end of the cord with polarity to the center positive for Space, negative for
Mark.

 - Select FSK mode, apply and hold positive voltage to the FSK jack, and
adjust C13 for 9.002295 Mhz. (Y2)

 - Apply and hold negative voltage to the FSK jack, and adjust C18 for
9.002125 Mhz. (Y2)

 - Select TUNE (puts the rig in CW mode and keys the transmitter), adjust
C16 for 9.000400 Mhz. (Y2)

Since all of the trimmer caps that affect Y2 will interact slightly, repeat
the Y2 adjustments at least once to ensure that all adjustments are correct.

As you can see, everything but LSB runs thru Y2.  It would have made more
sense to use Y1 for CW... don't know why they didn't.

The 'wrong' instructions for this tell you to use the wrong caps to adjust
the wrong modes.  A look at the schematic shows why it won't work.  For
instance, the "wrong" instructions tell you to use C10 to adjust CW...
except that the schematic (and the board) shows that C10 affects Y1 only,
and the CW-T mode sense line runs to C16 while the LSB mode sense line runs
to C10.  That's why the instructions are wrong.


Omni VI/VI+ TXCO Master frequency alignment:

The 'Ten-Tec' method of setting the TXCO is to use an accurate freq counter,
attached to socket #88 (or better yet, pin #1 of U13, which is the same
thing) with the probe grounded to the shield of this socket.  Adjust the
trimmer on the TXCO until the freq reads 10.000000 Mhz exactly.

My method uses an HF digital mode program waterfall display (I used MixW,
set to 'audio' display in the spectrum and zoomed in 4x), after aligning LSB
and USB on the TX Audio Board, tune to WWV on 10 Mhz in CW mode, hitting
'ST' to turn on the sidetone, and then adjusting the TXCO trimmer so that
the sidetone is zero-beat with the WWV carrier.  I use the eyeball to get
the signals close on the waterfall and then listen to the 'beat' of the two
signals coming in phase.  When the 'wow-wow-wow' has a period of longer than
one second then you are within one hertz... and you can get it darn near
exactly on freq.  Once this is done, check tuning by switching between LSB
and USB mode, and the 500 Hz and 600 Hz tones should be exactly in the same
place on the spectrum display when you switch between modes.

Why did I use WWV rather than my freq counter?  I trust WWV more than my
freq counter!

John Clifford KD7KGX

Heathkit HW-9 WARC/HFT-9/HM-9
Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
Ten-Tec Omni VI/Opt1

email: kd7kgx@arrl.net



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