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Old 19th Aug 2017, 8:55 pm   #1
AlanGI0OTC
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Default FT-101ZD Mk 3 Off frequency

Hello all,

Frequency is high by 6.7 kcs on all bands either injecting from a sig gen, or from the marker signal.
Pointing towards the VFO, any help would be very much appreciated.

Thanks.

Alan, GI0OTC
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Old 19th Aug 2017, 9:21 pm   #2
G4YVM David
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Default Re: FT-101ZD Mk 3 Off frequency

I'd have thought 6.7kc was good for a ZD! In fact, I'm amazed it stays as 6.7 and doesn't start as one figure and end up as another.

D
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Old 19th Aug 2017, 9:46 pm   #3
AlanGI0OTC
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Default Re: FT-101ZD Mk 3 Off frequency

Hi David,

Well it does stay the same, which makes me think there should be a way to bring it back closer to on frequency.

Alan
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Old 19th Aug 2017, 10:54 pm   #4
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Default Re: FT-101ZD Mk 3 Off frequency

Just a second.... windback a bit...

Do you mean that when you set to the ZD to a frequency as indicated on the digital display, it is6.7kHz off when compared to a known accurate marker or to a known accurate sig gen?

Or do you mean that there is a discrepancy with the mechanical tuning scale?

If you adjust the capacitors otr inductor in the VFO you will shift the frequency versus the mechanical scale, but the internal counter will move with the frequency.

You need to decide just where the discrepancy is before changing anything. And as David said above, 6.7kHz is good for a free-running VFO.

There is also the possibility of a slight error in mechnical assembly during some work (IE knob skirt rotated a little)

David
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Old 19th Aug 2017, 11:09 pm   #5
AlanGI0OTC
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Default Re: FT-101ZD Mk 3 Off frequency

Re...Do you mean that when you set to the ZD to a frequency as indicated on the digital display, it is6.7kHz off when compared to a known accurate marker or to a known accurate sig gen?

Yes too the above. It's repeatable and has been this way for quite some time. Just wondering if I can pull it down with the trimmer in the VFO ?

Alan
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Old 20th Aug 2017, 7:27 am   #6
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Default Re: FT-101ZD Mk 3 Off frequency

If the digital display on the 'ZD says the right frequency and the set is off frequency, then your error could be in the reference frequency crystal of the counter.

I've just hunted down a block diagram and the counter counts the output of the premixed LO, so any error in the premix crystals is also accounted for. If the set isn't on the frequency displayed, either the carrier crystals and the IF filters are off-frequency or else the counter reference is sulking. So don't touch the VFO, it's probably innocent and you don't want to disturb its linearity or temp compensation.

David
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Old 20th Aug 2017, 10:08 am   #7
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Default Re: FT-101ZD Mk 3 Off frequency

I think it might be the display or signals to it that are in error.
I have one of these and upgraded it to "D" and I have had a similar problem at some point.

If I remember correctly, the display has to calculate the frequency based on what it measures. There are a number of offsets to take into account and one of them is the LSB USB aspect so there is an input from the mode switch and it applies a suitable correction based on that. If that signal is wrong then you get the wrong value dispalyed.
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Old 20th Aug 2017, 11:21 am   #8
AlanGI0OTC
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Default Re: FT-101ZD Mk 3 Off frequency

Thanks for input guys. I have measured the counter reference frequency, the XTAL is marked 6.5536 and it's reading 6.55342 the highest I can adjust it.
I suppose the crystal has aged, is there a way to pad it enough before it stops oscillating?
Any suggestions welcome.

Alan
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Old 20th Aug 2017, 1:10 pm   #9
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Default Re: FT-101ZD Mk 3 Off frequency

A bit of trial and error with small value caps around the crystal? Just a thought, is the counter you are measuring with calibrated? The error could be in your test gear! Apologies if I am stating the obvious.
Alan.
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Old 20th Aug 2017, 1:28 pm   #10
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Default Re: FT-101ZD Mk 3 Off frequency

Be careful with the counter chip, I believe all known stocks of spares have been used-up.

If your measurement is accurate, then the crystal is 27.5 ppm (parts per million high in frequency) Not too bad. More like ageing than a fault. Ageing in quartz is an asymptotic Approach to a 'final' value at infinite time. So it does so much ageing in the first day, then the same amount spread over 10 days, then the same amount spread over 1000 days and so on.

To reduce the frequency, try small value inductors in series with the crystal.

David
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Old 20th Aug 2017, 1:46 pm   #11
AlanGI0OTC
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Default Re: FT-101ZD Mk 3 Off frequency

Yes the measurements are accurate, counter, spectrum analyser and signal generator locked to a GPS disciplined 10Mhz standard.
The oscilloscope is also in calibration, as is the multimeter etc.
I don't often operate on vintage equipment, hence the queries. PLL and DDS are so much simpler ��

Thanks for all the tips.

Cheers
Alan
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