On Tue, 28 Sep 1999 22:51:24 +0100 "Steve Baron - KB3MM"
<SteveBaron@starlinx.com> writes:
>
> What is your 'secret' to the pretty good system ?
>
> Is the problem temp related ? Or just aging ?
The trick to getting an Omni-V calibrated is to make it a lifes work. HI
HI
Well at any rate it does take time. I have lots of notes on it that I
could go into however I don't know if this List has the room on it or if
there is enough interest. Some things that are important are to do the
calibration at the operating position for the rig, temp has a lot to do
with it as well as moving the rig around. I also found that the Omni
likes some room to breath around it , I'd say 6" over the top and 3" or
4" on the sides just to keep the ambient temp down. Not to split hairs
but if it is to be "dead on" these things help. I would never expect an
Omni-V to come back from service and be right on everything, due to
handling but most will be in spec. For good reciver performance in a
stock rig the BFO trimmers must be on proper freq. and the PBT oscillator
must be very close to design freq. with the control knob centered. I use
a Beckman Industrial freq. counter,(DON'T try to do any of these
adjustments by ear or guessing it just won't work!) it has a 10Mhz xtal
in it for the time base which I can zero to WWV by coupling it to the
receiver. I have drilled a small hole in the top of the counter to adjust
its trimmer after it has been on over night to warm up. I check it
first, then after the rig has been on several hours in the operating
position in the shack I remove the top and put my counter probe on the
BFO to read the 9Mhz. put the cover back on and with the counter on line
let it sit till there is no drift in 20 mins or so. Every time the cover
is removed and replaced I wait for everything to warm up again. I leave
the trimmer tool in the rig as well to keep it warm I'm not happy till
the LSB stays at 9.000.000 Mhz and USB is 9.003.000 and CW transmit it
9.000.600 ect. till all the BFO freqs. are good. The PBT alignment is a
bit tricky due to having the lower cover off and turning the rig up on
its side but I find the temp does not bother that so much. With this
counter and some trial and error I've found a good means to calibrate
every board on the Omni-V, all the xtals and trimmers are temp sensitive
but there is a way to keep them at operating temp and adjust them.
I also find that under normal use (I'm not a contester) the heat from the
finals has little effect on the xtal oscillator settings as long as the
heat has a place to go. There is some warm up drift on the band xtals and
some bands have more than others but I don't think any are more than
200hz cold and they all come in to less than 10 hz after a 1/2 hour just
receiving.
Steve I don't know how much the drifting has to do with xtal aging but I
do know temp and time both play on the calibration. The more I learn and
adjust my Omni the less it seems to need so I think a lot can be said for
proper alignment in the first place.
You guys let me know if you'd like some input or my shop notes on the
Omni-V. The thing I like best about this rig is it has very good
performance and still be at a level that even a shade tree tech like me
can keep tuned up.
The Omni-V will work well without being this nit picky but oh, the sound
of one after a good alignment. It'll make your head swim!
73 to all AA8VE -Jeff-
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