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DX-959B 10.240 VCO Refference Circuit


That is what the var cap is for. But the question is stability as they can/do go bad in older versions of this radio. Since you are dealing with a new radio, it shouldn't be an issue. Be sure that you let the radio warm up for at least 40 min before you make any adjustments - especially true for Galaxy radios - IMO.

But now that you've adjusted the ref osc xtal; the fun begins . . .
 
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The Galaxy is the bandwidth of the drift. Exit Thirteen is the anti-drift expert. He has a fix for the drift problem. Just change out some caps to better quality and re-align.
I had a brand new 959 warmed up for an hour, did the alignments for AM and SSB and by the time I finished it had drifted about 20 Hz off of the set points. Still in specification but disappointing.
 
Im still messing around with my new DX-959b and I checked the VCO circuit and it was set at 10.245. Is that off far enough to cause a problem with the PLL? I dialed it back to 10.240 just in case.
Yes sir. 5Kc off will screw the SSB to the point where it won't work properly.
 
i just hope the settings for the older 959's on cbtricks havnt changed on this new radio. I think its total bs that ranger, galaxy and others dont put out updated service manuals. I know this is part of the reason that most dealers stopped selling RCI Ranger radios now.
 
The Galaxy is the bandwidth of the drift. Exit Thirteen is the anti-drift expert. He has a fix for the drift problem. Just change out some caps to better quality and re-align.
I had a brand new 959 warmed up for an hour, did the alignments for AM and SSB and by the time I finished it had drifted about 20 Hz off of the set points. Still in specification but disappointing.
IIRC, Xit13 pointed out that to remove C130 altogether and to replace D49 (a SVC251 varactor diode) with a 1S2687 varactor diode (used in the Cobra 148GTL and other Uniden chassis in its day - no longer available) to make it more stable. This will also slightly limit the range of the clarifier; but in turn will stiffen the loose drift.

If you know more than that mod to bring more stability; then please let me know - too.

drift.PNG
 
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I don't know if this still hold true, but every crystal oscillator circuit usually has a capacitor in parallel with the crystal. Is there something missing here?
http://electronicdesign.com/analog/fundamentals-crystal-oscillator-design

A different load capacitance will produce the wrong frequency.

74397_fig4.jpg


4. The load capacitance is the capacitance “seen” across the crystal’s terminals, exclusive of the internal shunt capacitance.
 
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Im still messing around with my new DX-959b and I checked the VCO circuit and it was set at 10.245. Is that off far enough to cause a problem with the PLL? I dialed it back to 10.240 just in case.
Maybe I'm Wrong here, but did you make sure to let everything warm up for a while before checking & adjusting?
 
Do not use your MFJ antenna analyzer to check, align your radio. The analyzer is no where near accurate enough for this application. Most of the MFJ antenna analyzers will be off anywhere from 3 khz to 8khz, which is more than adequate for antenna work, but not radio alignments.
I have, and use two Fluke 7220A frequency counters that are lab calibrated and certified for alignment work.
 
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Yes, it had been on for over an hour. I checked it with the counter built into my MFJ antenna analyzer, so the accuracy may not be the best. I will check it later after my good Fluke counter gets back from the calibration lab.
That 'counter' in the MFJ wasn't meant to be used for definitive testing or alignments. It does not have enough resolution for alignment work. It displays only '27.385mhz' (for example); and not 27.385.000mhz - which is what you need to align radios.

IOW, it cannot display enough freq detail. The Service Manual calls for +/- 20hz accuracy for aligning the radio, which is just not possible with the MFJ unit. Keep in mind, that 27.385mhz is read as 'twenty-seven million three hundred and eighty-five thousand hertz'.

Sooo, if you adjusted the 10.240mhz (which is actually 10.240.000hz) osc xtal with the MFJ, you are probably still way off the +/-20hz tolerance that it allows for. You cannot see that part of the freq because that counter doesn't have enough resolution to display it.
Capture.PNG
 
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