Galaxy radio drift

[Handy Andy]

The "twin diode" is from a Galaxy 33HML - several others use the EPT360014B board, but I have a SS3900 that is a 360011Z board uses similar - so the older days, the PLL used the capacitance to it's advantage.

Couldn't tell you the numbers of the parts used on that - buried in wax...

 

[Robb]

If you are working on one of the non-DX radios; then here are a couple of thoughts:

Changing out the SVC-251 for another diode that has less capacitance will keep the drift down (like the variety that Uniden radios used in the 80's-90's). The more capacitance your varactor has; then that same capacitance accordingly translates to more possible freq drift.

These radios drift due to the way they were designed, and there is no fix at all for them. Let us know if you find it; because I wasted far too much time attempting to do the same thing. I went over the ENTIRE loop osc trying better grades of parts and spent more than a few bucks in that process. I overturned every stone I could, and there is a thread somewhere on this forum that I documented all that work. Best of luck . . .

Heat and cold are the culprits; the more extreme the cold and heat are; the more they will drift up or down in either direction. You can try to limit the range of the clarifier instead of trying to increase it, as this will also limit the overall amount of drift.

Just saying . . .

 

[Larry A McClanahan]

Yep, I agree. But I just discovered that on the Ranger 2950 it has a factory instatted 5p cap across the pins of the Crystal in the final oscillator and then I remembered an old tech had told me when I was a kid that he was doing it to stabilize the circuit. Anyone ever hear of this?

 

[Larry A McClanahan]

Before you do anything with these you need to solve the heat issue. That can easily be done. Then you have to move on to the stabilization of the circuit itself. I am hoping that 5 p.m. capacitor I put across the crystal solves the problem. So far, so good.

 

[Tallman]

The 5pf cap is a standard part on many designs. It is used to stabilize the crystal.
The calibration reference I have has signals that look like this. The capacitor removes the "Fly Wheel action" from the low voltage around the crystal. The following photos are from the vendor I bought one of these from. https://www.ebay.com/itm/10-0000-MH...uQAAOSwB4NWxX2W:sc:USPSFirstClass!40219!US!-1

I built this circuit and had it calibrated by a laboratory that is NBS traceable. I use it as a transfer standard to check my frequency counters before doing alignments.

The signal after processing through the TXCO Oscillator.

 

[Martian]

Solving the heat issue on this design is easy. Throw it out.

This is a problem I have resolved. It's just beyond the scope of a CB tech to do so.
The alternative is to do what Lester @ Lesters customs has done which is build an oven. That will cut the drift down substantially.

 

[Larry A McClanahan]

Interesting word, stabilize.
Throwing it out is really not an option. We're talkin CB radio, not amateur. We are also talking about an entire line of radios, the DX series.

I have found that after I completely solve the heat issue, the circuit is just about stable. Now I have put the 5p capacitor across the crystal posts. So far, I'm getting no drift.

 

[Martian]

Unless your compensating for temperature. It drifts.
Fact of life.
Just a question of how much.

 

[Shadetree Mechanic]

I saw somewhere where someone put a light bulb inside the radio as an oven. Is this all that needs to be done? Sorry for the noob question.

 

[Martian]

That is a crude fix but it would make it more stable.

All radios drift because all crystals age over time.
The only thing we can do to minimise it is to age them and put them in temperature controlled environments.
That's what the light bulb is sort of doing. Once it warms up it will become more stable and drift is minimised.
Some inexpensive parts and styrofoam will work wonders on these.
Getting some new crystals with tighter tolerances works too.

These radios will drift often by hundreds of hertz over time/temperature.
With temperature control you can get it down to tens of hertz, possibly single digits.

 

[Larry A McClanahan]

I tried the light bulb oven. I believe it was 6.8 volts on a 12-volt wheat bulb that I got the desired temperature which was around 110 degrees.
The only real difference between the two circuits, Ranger 2950 versus Galaxy 959 is the 5p cap across the Crystal posts.
Ranger must have known something that Galaxy did not. This is day number two talking on it. So far, no drift.
And of course I put a heat sink on the back of the radio.

 

[Handy Andy]

I deal with Low-Budget - Indie-type of installs...

They don't have the $$$ for ovens and kits or radios that survive nor the environment conducive for it - you have to look at the bigger picture.

Not many have resources available like some one us have been blessed with the knowledge on how to use and understand the process. They just want to get thru the day.

I just use a light bulb on a switch for cold mornings in mobiles - else Base radios - turn on the desk lamp and aim for the case, just let the thing warm up for about 5 minutes. Laugh if you want, but it works.

Heck, even a desk lamp shining down on the case of the radio can help remove the humidity effects and stabilize the parts and their compositions without have to "oven" the Xtal - which still doesn't fix the external controls. Those again are environmental effects affecting (the external) that which has some benefit of stability (the internal) - but is it worth the cost?

I'd rather have the radio act up in warm-up periods, for they are indicators of further problems getting worse. A noisy pot can be cleaned and re-lubed. But component failure? Although moot - at least by observation of the warm-up process, we can gather a lot of information alone in observing the symptoms - for one symptom may indicate a particular part, but is that the part that's is causing the problem? Not in all my experiences, hence the "shotgun" approach I take - not all symptoms are dealing with one part, there are many in the chain to choose from.

But with that out of the way...

I wanted to say, that out of all the drifting issues I have had some across my desk, the biggest culprits are...

Maximum slide - meaning the pot the operator turns, is the one that is "Volted" to buss and to ground with nothing in-between to stop it.

They never realize the effort of the Voltage divider circuit - the potentiometer is placed in the middle of, for the sake of linearity on the front panel control range.

It is so painful at times to see how some radios are so spaghetti-ed on the front panel, to bypass this and go here to get that approach, I've spent hours - if not days, undoing all of it to bring it back to stock, only to find out that somewhere along the way, putting it back to stock fixed the problem and the radios' acting normally again.

How do you charge a guy like that? By the hour? Or just give him a radio they can't do all of what they did to this one you just fixed? Sell the one you just fixed to someone else that will appreciate it for what it is and not mess with it - boy those days are fewer and fewer....if youtube is an indicator.

Anywhoo...

When you guys start talking about "tuning" and stability - there's always the variables yes, but, when the end user decides to "go for broke" - usually winds up making the radio "broke" because they exceeded limitations on voltages.

Varactors, for what they are - are wonderful devices but only exhibit their true reasons as to why we like them, thru a narrow range of voltage. They don't need much current, they're reverse biased so they simply act like a tuning capacitor when presented to a Crystal - which then reacts to that, and we gather that energy and put it elsewhere in the radio to use.

Here's what I'm talking about - a couple of charts some of you may recognized these so I won't bore you but to the rest - what I want you the curious one, to see is how much we have to apply to make the change in tuning that provides the range of band we can tune...




Look at the highlited in yellow areas, that is a tiny amount of capacitve change for a wide voltage range. The effort only gives you a small amount of capacitive reactance to make the series circuit with the crystal - change it's resonant frequency...

But, that's for Clarifier - we don't want or need a TON OF SLIDE if we were to just tune into someone within the channel itself - so that is why the level of change ratios are so vast compared to say...something you need a PLL to use...


It really hope all of you are caring to notice - the following...

The largest range of capacitance is in a small range of voltage - note the slope of this rate.

The greatest change in capacitance is when the voltage to it is less than - not more than, the effective SAFE OPERATIONAL AREA (SOA) of all the parts involved.

The Clarifier is a voltage divider - if we set other FIXED resistance above and below, we can effectively meet the maximum rate of change within a small range of voltage to achieve the adjust slide we want.

The best and most stable clarifiers use the smallest change of capacitance used in the entire range - helping to reduce drift.

PLL circuits can use the maximum rate of change in a small window to obtain their best stability AUTOMATICALLY thru their loops and phase detectors. So large value varactors give you the best ability of the PLL to maintain the frequency it is set to use.
​

So we need to quit making clarifiers with TONS of slide that get us into stability and warble troubles more than they're worth in slide - due to the constant changes we need to make as an operator to stay on frequency - it is our responsibility to keep us "dialed in" - no one wants to talk to some one that can't stay on frequency.

:+> Andy <+:

 

[Martian]

Yes. the unintended consequences of volting radios.

@Handy Andy you don't need to go out and get ovenized crystals but yes, that's an extreme. I got them down to a few ppm with simple heaters. No muss, no fuss. one or two dollars in parts. No extreme parts changes.

 

[Robb]

The only time a Galaxy radio drift is any kind of an issue, is when the environmental temperature changes suddenly. If the radio is left on in a room in your house where the temperature is stable; then there is no issue. If it is in your car; then that becomes a can of worms that no internal oven will help.

Example: If there is an incandescent light/oven in the radio and the temps are cold outside and initially in the vehicle before the vehicle's heater is turned on; then it will reach an internal temp that will be heavily influenced by whatever the external temp of the radio case is, since that same external case temperature (either hotter or colder) will either cool or heat that same case.
So, that is not a viable solution either.

I keep a 959 on all of the time in the house with climate control, and it almost never moves freq unless there is a change around it. Now the Galaxy radio in my car is very unstable unless I turn on the heater when I start the car in cold weather; or the air conditioner in hot weather.

The loop osc xtal is not the only part in that circuit that will cause drift if the temp changes suddenly, so insulating the xtal is equally useless. The resistors and caps also shift the temp around. In fact, there is a temp compensating cap in the loop osc circuit; it has the designation of 'UJ'. Look at the schemo and you will find it.

 

[Handy Andy]

I like that approach.

I've been dealing with less and less inventory of a simpler surface mount pot that like the PC-122 mounts in tangs on the surface of the front panel - because they want to "volt" the pot versus just changing a few internal parts to make the slide more - not blow up due to current draw thru the substrate because of their jumper mods.

The sad part about all this - is the parts involved were the best choice for the radio and still are, the technology is gone ahead and left them obsolete - so the rest of us are dealing with less and less inventory to repair the older radios - we have to rebuild them - and we can only go so far in doing that.

So the post was more about keeping things set up in a original concept of within the channel versus the in-between channel approach - you can make do with those changes in other ways (10kHz skip stuff).

The "Bane" Galaxy; had, has, does, is currently - is the "dual concentric" - you know - the Fine and Coarse. Seems people love to use them - so I'm ok with that, just wish "coarse" wasn't the one that gets these kids into the lazy thinking of cheap way to get tuned in. They don't know how it happens until you tell them how the temperature and humidity can affect the tuning the Galaxy's got. One minute they're talking to someone the next minute we hear fuzzy screaming of - "WHERE DID EVERYBODY GO?" that's' drifting into another channel because they don't know or weren't paying attention...

So, let the PLL do it's job, and make the Clarifier slide be enough but not so much that the user can get lost, or find themselves on another channel interrupting a QSO the others were avoiding in the first place - some things can get said than can't be unsaid...

I'll leave it at that...

:+> Andy <+: