DRIFT, DRIFT, DRIFTTTTTTTTTTTTTTTTT

[Grogan]

I hear complaints of radios not being stable on SSB but I don't run a SSB radio mobil where the ambient temps change. In the shack on my radio I see 27.3950 to 27.3951 or 27.3949 that is stable If my Galaxy was in the modil what should I expect to see???? DX-979 With A pro Tune...

 

[Robb]

With a professional tune, it will still drift just as much as without a tune would, So long as the clarifier is unlocked you can still pitch it up or down as needed. I run a Galaxy in my mobile and have for years. Just get used to using the clarifier is all that is needed . . .

 

[M0GVZ]

Indeed. Unless you change the crystal for a temperature controlled oscillator it'll drift.

 

[Tallman]

There is a member here that has found that there are a few capacitors you can change and stabilize it. Need full alignment afterwards.
The "Wizard of PLL" is Exit13. Use the search feature and you will find those discussions.

 

[9C1Driver]

If it were that simple I would think this would have been being done to Galaxy radio's for 20 years now.

 

[ExitThirteen]

There are 3 things that will drastically reduce drift in a galaxy radio. First replace the varicap diode(s) with 1S2687 diode(s). Second, there's a range limiting capacitor that's parallel with the varicap diode that needs to be removed. Third, the 15.360 crystal needs to have a TCXO in its place.

On a 979, depending on the weather, it can wander as much as 1.5khz during warmup. Robb and I have been throwing ideas about on how to correct this issue.

Right now, I'm working on a 949 and I have changed out the varicap diode and the range limiting cap that parallels the diode and right now during warmup at room temperature, it only wanders about 50-60hz, which is not bad. I haven't experimented with cold weather yet, but will put the radio in a the freezer for a half hour to an hour to simulate cold weather, and see how much it wanders then.


~Cheers~

 

[9C1Driver]

That sounds promising, thanks for the information.

 

[M0GVZ]

There are 3 things that will drastically reduce drift in a galaxy radio. First replace the varicap diode(s) with 1S2687 diode(s). Second, there's a range limiting capacitor that's parallel with the varicap diode that needs to be removed. Third, the 15.360 crystal needs to have a TCXO in its place.

The only thing that is actually achieving anything in regards to stability in all of that is the TXCO. It is the oscillator that causes drift so thats what you need to concentrate on. Neither the varicap diodes or range limiting capacitor have any effect.

 

[Robb]

There are 3 things that will drastically reduce drift in a galaxy radio. First replace the varicap diode(s) with 1S2687 diode(s). Second, there's a range limiting capacitor that's parallel with the varicap diode that needs to be removed. Third, the 15.360 crystal needs to have a TCXO in its place.

On a 979, depending on the weather, it can wander as much as 1.5khz during warmup. Robb and I have been throwing ideas about on how to correct this issue.

Right now, I'm working on a 949 and I have changed out the varicap diode and the range limiting cap that parallels the diode and right now during warmup at room temperature, it only wanders about 50-60hz, which is not bad. I haven't experimented with cold weather yet, but will put the radio in a the freezer for a half hour to an hour to simulate cold weather, and see how much it wanders then.


~Cheers~

What value did you choose for the cap paralleling the varactor diode?
Or did you remove it altogether?

I can put the covers back on the radio after aligning the oscillators, and it will immediately go off freq due to the shift in the tuning cans inductance. Bam - just like that! Those cans are still at the core of the problem, and I have no remedy for that. I know C282 can be slightly increased to balance off that effect IIRC.

 

[ExitThirteen]

Robb,

I simply removed the range limiting cap, as it is not needed.

~Cheers~

 

[AL567]

Drift and Galaxy. A marriage made in heaven that will never divorce.

 

[JCH]

Drift and Galaxy. A marriage made in heaven that will never divorce.

And I'm ok with that. Lol.

 

[hammer0630]

They say a Ford Pinto can blow up in a rear end crash but I don't put gas in it. Is this a answer to a bad question and a ok answer????? If you are not affected why so frustrated lol.

 

[Mudfoot]

Drift and Galaxy. A marriage made in heaven that will never divorce.

I've had several Galaxy SSB radios in the past 6-7 years. I might be the exception, but I don't recall any of them drifting so bad that it bothered me. My 94HP seems to be pretty stable.

 

[Robb]

I've had several Galaxy SSB radios in the past 6-7 years. I might be the exception, but I don't recall any of them drifting so bad that it bothered me. My 94HP seems to be pretty stable.

The word 'drift' may be a misnomer here. "Shift' might be more appropriate to use. When these radios are first turned on, that is when the shift from center freq is realized. Until the radio's chassis reaches parity with whatever ambient temp is present after components heat up due to current draw, it will then 'drift' to that center freq. Now - of course - all radios shift and drift. However, a Cobra 148GTL will do this far less than any Galaxy will; and sometimes isn't even noticed if the temp is close to the temp of the room when the radio was originally aligned. Unfortunately, one cannot say that about a Galaxy.

If the Galaxy engineers had designed the Loop Osc/Output Osc circuit closer to the 148's chassis; then this subject would have little reason to be mentioned at all. Never had nor worked on a Galaxy that didn't have considerable shift and drift. Never.

Of course I'm sure you know all of this. But you raised a good point for any newbee that wants to understand what is happening when this subject has been raised,, as it has been done here.

You live in the mountainous area around W.VA/OH IIRC, Mudfoot? Since temps can range wildly in a mountain environment, you should see a greater shift on a December morning then those of us living on the W Coast would know. It is all relative to the temps around you . . .