[Moon-net] IC746 frequency drift

["Heinz Bordé"]

Hi all
I have had the same problem with my IC 746.
First I tryed the TCXO CR 282. It didn´t help.
Then I filled the whole quarz compartment with cotton wool, stolen from my wifes bathroom.
That helped in my case. WSJT is no problem anymore.
>From my point of view the problem is not the cristal; the problem is the coil for setting the crystal. And that coil is sitting in the air stremm of the blower. The cotton wool prevents the air from blowing trough that little compartment.  The coil thinks the blower is off and doesn´t react anymore.


    73 Heinz, DM2BHG


"Michal" <sp2iqw at e2000.gdynia.pl> schrieb:
> Hi all drifting 746-ers
> 
> As long the inside temperature will move up and down during the 
> transmit/receive operation the frequecy drift will occur.
> Costless cotton advise helps slighly with this problem. Purchase of 
> Icom's CR-282 or CR-338 OCXO is an expensive way while the "crystal 
> heater" from DB6NT well stabilize crystal temperature so minimize drifts 
> at a friction of CRxxx cost :-)   This solution can be used with other 
> radios as well.
> See http://www.kuhne-electronic.de/english/special.htm >> "crystal 
> heater". 
> Below  is a desription taken  from  Kuhne Electronics GmbH 2006/2007 
> catalog:
> 
> /This precision crystal heater provides temperature compensation for 
> crystals, usually found within crystal oscillators. The circuit, which 
> is built on AL2O3 ceramic substrate, has to be mounted on the 40°C 
> thermostat crystal using heat shrink tubing. The circuit heats the 
> crystal to a temperature of 40.8 °C with an accuracy of better than 
> 0.1°C. This provides high frequency stability over the temperature range 
> of -5 to +40 °C. This crystal heater is a good alternative to completely 
> heated OCXOs, however, the values of an OCXO cannot be achieved./
> 
> Thinking about external 60MHz freqency source I have concluded that such 
> solution will be not worth an effort it needs. Supposing that short term 
> stability problem is solved I need only to check from time to time 
> absolute accuracy with external standard.  That is another story, good 
> starting page is: http://www.ve1alq.com/cpldpll/cpldpll.htm  (I plan to 
> build 100MHz VCXO controlled by 10kHz taken from an old Rockwell Jupiter 
> GPS board).
> 
> 73, Michal SP2IQW
> 
> 
> 
> David Hilton-Jones napisa?(a):
> > Dear Anatoly and others interested parties.
> >
> > I followed Anatoly's advice and wired the cooling fan so that it is on
> > continuously. To my very great disappointment it hasn't solved the
> > problem - not only hasn't it improved the drift, it has if anything made
> > it slightly worse!!
> >
> > When running full power, within a few seconds of going to transmit, the
> > frequency moves up 3Hz. Over the next 45 seconds it gradually falls, and
> > ends up 10-15Hz below the starting frequency.
> >
> > When running low power the problem is much less marked. Anatoly, I
> > wonder what output power you are running?
> >
> > As noted, with the fan running continuously the drift is probably a
> > little worse at high power - I guess because the stating temperature is
> > a little lower because of the fan.
> >
> > So, it's back to the drawing board!!
> >
> > Any other ideas gratefully received. Has anyone resorted to an external
> > 60MHz source? It's a great pity, because overall I prefer the rig to my
> > TS-2000.
> >
> > 73
> >
> > David, G4YTL
> >
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> 
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