The Omni series has oscillators which are xtal controlled while the Icom
uses pll technology. Each band in the Omni requires a xtal to provide
frequencies for the first mixer and there is a 9mhz osc for the bfo/tx
osc. Plus the time-base reference osc. found in the Omni V and VI. I've
found the bfo to be the major drifter in the newer Omni's and the PTO to
be the major source of drift in the older ones. Don't get me wrong. We are
only talking about 50 to 100hz drift here!
Here's how to check for drift. Tune in wwv, setting the pitch of their
carrier to about 700hz. Switch in a dummy load and begin transmitting for
about 10 minutes straight using cw or just hold down the key for a few
minutes. Now go back and listen to wwv. Has the pitch changed? If yes,
repeat the experiment with the top cover removed and note the difference.
I have found the Paragons to be a little more stable than the Omni
probably due to the PLLs. Personally, I would rather contend with a little
drift than listen to a PLL rig for long periods. There is a difference!
>
> It seems curious that you need to ventilate the cabinet to control drift.
>
> My Icom IC-765 (sorry to be using bad words here!) with its internal
> switching power supply is almost completely sealed with no interior air
> flow or ventilation to speak of. I operate it 24/7 on a computer UPS in
> order to keep the calibration, etc. stable with little or no discernible
> drift. The cabinet runs very slightly warm on top. The external heatsink
> seems to do an adequate job - with its internal fan - of dumping excess
> heat while transmitting.
>
> Stability is more than adequate for routine ham operating without the
> 24/7 mode, but since I work digital modes, etc. it is convenient for the
> radio to always be stable whenever I want to operate.
>
> What does TT say about the drift vs ventilation situation? Are their
> radios not designed to be operated without external cabinet ventilation?
>
> I am not trying to slam TT radios - just curious . . . ;^)
>
> 72/73, George AMA 98452 R/C since 1964
> Amateur Radio W5YR, in the 54th year and it just keeps getting better!
> AutoPOWER Systems, Fairview, TX (30 mi NE Dallas) Collin County
> QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X 33.2 N 96.6 W EM13RE
>
>
> Steve Ellington wrote:
> >
> > I think most TT rigs are air deprived. The Omni 6's I had needed some air
> > inside badly. When receiving, it was stable but after sending for a few
> > hours at high speed, the oscillators would drift due to heat conducted
> > from the finals. There were 2 cures. One was to keep a fan blowing across
> > the heat sink on the outside and my final cure was to remove the speaker
> > and install a small fan in the bracket. It fit perfectly and blew air out
> > the speaker grill. I used a 24v fan from an HP printer. It was virtually
> > silent and stopped the drift. When I sold the rig, I simply removed the
> > fan and put the speaker back in it. The corsair and Omni A-D series were
> > sealed up with no velilation too. The same thing happens with them after
> > transmitting for a while and I'm going to do something along the same
> > lines. A cheap solution is to leave the lid off but maybe one could get
> > the lid perferated somehow. About 200 holes would do the trick.
>
> --
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>
>
Steve Ellington N4LQ
N4LQ@IGLOU.COM
--
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