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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 28th Dec 2018, 9:23 pm   #21
Ian - G4JQT
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Default Re: Xtal digital replacement

I recently saw a mention of CARDINAL CPP oscillators. Not quite sure what they are, but I think you buy them pre-programmed at the frequency of your choice.

Now looking for some basic ''what are they and how to use them'' info, and not just data sheets...

Ian
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Old 28th Dec 2018, 9:36 pm   #22
Colinaps
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Default Re: Xtal digital replacement

I have heard of being able to listen to the crystal with a receiver while grinding. Any truth in that?
73
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Old 28th Dec 2018, 10:12 pm   #23
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Default Re: Xtal digital replacement

Yup. been there, done it.

Multiple crystals are ground immersed in abrasive slurry in a sort of spirograph machine. the grinding is a broadband noise excitation and piezo electric effect creates an electric component to their resonance. On a receiver it sounds like a band of filtered noise. It's not ultra precise, but gets used as an indication when they are almost there.

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Old 1st Jan 2019, 12:02 am   #24
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Default Re: Xtal digital replacement

The crystal grinding from 1.595Mhz to 1.985Mhz has now been completed. I stopped about 400 hz short of the final target because I want to test it on the final transmitter and to allow for any short term drift. AM top band won't notice a few hundred hz and overshooting was not what I wanted after many hours work.

For info this was a large 10X crystal.

Start : 1.595Mhz Thickness: 1.03mm
End : 1.985Mhz Thickness: 0.82mm

This is the first crystal I have ground and I don't claim to be an expert but this is the method that worked.

1. Mark one face with a small pencil mark or marker so that it can be identified. This face is not ground to preserve one manufactured face.

2. Place the quartz on a wetted diamond tool stone #400 grade datum side up with one drop of water on the quartz. Then place the metal electrode from the 10X case on top of the crystal. Very important the electrode raised corners MUST be UP away from the quartz or you will grind the corners through extra pressure in those areas. gently press down . The tolerances on mine were so good that the quartz is now stuck to the metal back plate forming a perfect support for grinding. Note my stone suggested that it could be used wet or dry but I chose wet to reduce any chance of breathing in quartz dust.

3. Comence a fiqure of 8 grinding pattern turning the quartz angle every so often to equalise any biases on the stone and only put pressure in the center of the backing plate. The object is to preserve the parallel thickness during the grinding. (My stone was just a hardware store one not one guaranteed to any degree of flatness)

4. Periodically clean the quartz and check the frequency. I had to gently slide the quartz off of the metal backing as it really stuck well.
My test rig was a dip meter and a small frequency meter with the quartz slid back into the holder. It was not necessary to fully slide in the metal spring.

5. I used ordinary water to wash the plate.

6. Repeat many times!!

7. If the activity drops off or the oscillations fail to start ensure the slab is clean and dry also try GENTLY chamfering the slab edges , all 8 sides. I had to do this twice.

8. Use the fine diamond grit #1000 side of the stone to gently finish the grinding . Note a fresh stone is more abrasive on first time use until it settles down.

The finished and fully assembled crystal appears to have the same activity characteristics on the test rig as untouched sealed crystals. But the real proof will be on the target transmitter, an early valve receive and valve transmit Ajax ship to shore radiotelephone.

Pete
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Old 1st Jan 2019, 1:17 am   #25
Terry_VK5TM
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Default Re: Xtal digital replacement

While it seems a lot of work and was the norm way back when, I can only imagine the thrill of successfully having accomplished this for the first time.

Well done.

Hope the rest of the project goes as smoothly
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Old 1st Jan 2019, 10:52 am   #26
Bazz4CQJ
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Default Re: Xtal digital replacement

This takes me right back to grinding 6 and 8Mhz FT243's for use on 2m 'back in the day'. The only thing we did differently from you Pete was to do a final rinse in IPA after cleaning with water and then a final drying, by the sophisticated technique of wrapping the crystal in some cotton wool, putting it in a match box and wedging the box next to the 60W bulb of a desk lap and leaving for 10 or 15 minutes. The rationale was that the crystal would be most stable and most active if it was perfectly dry. I don't think there was hard evidence that this was true, but it's unlikely it did any harm. Even after being multiplied up by x18 to come out on 2m, the results were good.

B
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Old 2nd Jan 2019, 12:49 pm   #27
Steve G4WCS
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Default Re: Xtal digital replacement

nice work, glad to see them being used. nearly threw them out in a clear out years ago, glad I didnt now
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Old 2nd Jan 2019, 3:16 pm   #28
G6Tanuki
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Default Re: Xtal digital replacement

Good to hear you have had success and the result oscillates nicely on the desired frequency!

I'm told that if you over-do the lapping and the frequency is higher than you intended, you can drag it down a bit by rubbing the faces of the crystal with leaded solder or a 'soft' graphite pencil.
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Old 13th Jan 2019, 8:29 pm   #29
G4_Pete
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Default Re: Xtal digital replacement

Hi Just thought I would give the final close out on this.

I put the crystal in my Ajax marine set ( Fully electrically restored ) and keyed up into a dummy load. It worked on frequency but there was about a second delay before the drive to the PA valve built up. I concluded the crystal may not be active enough and only just getting above the required loop gain.


On re watching the old Black and white crystal manufacturing videos on YouTube I saw that the crystals at the final test and acceptance stage had the edges beveled to increase activity. This I did with disastrous results. No oscillation in the transmitter and a 800Khz jump on the Dip meter test.


I put the crystal back in the oscillator and with NO HT or LT and drove the low impedance cathode with a signal generator whilst monitoring the valve grid with a X10 probe and oscilloscope. At 1 Hz steps I could clearly see I now had two peaks .


By undoing the bevel very carefully a few gentle rubs on the edge over the stone I gradually restored the single resonance back on frequency. Further very slow and careful edge grinding and re testing as above gradually saw the Q increase.

I marked all the parts of the holder and crystal with tiny marker dots and then cleaned and dried the parts as clinically as I could. I re assembled the holder and did the "Cold" oscillator test at 1 Hz steps. Half the amplitude that I had before!!!!!


Very despondently I took the crystal apart again checking for dust ,all clean. Looking at the crystal I noticed a tiny bit of finger print , I cleaned it again in soapy water and dried in a cool oven, re assembled and the Q had returned. On power up there was no key up delay and the TX was on frequency.

These screws are NOT coming out of the crystal again.

I guess somehow within the geometry of my hand ground crystal beveling the edge permitted dominance of one part of the wafer over another leading to the Dip meter jumping in frequency and the double hump when the frequency was swept. As for the Q reduction and the grease spot I am guessing that this is analogous to guitar strings where old greasy ones are dull and clean new ones have a bright sound. The G force and dampening effect on the spongy grease at 2 Mhz being large enough to severely impact the Q.

Next challenge to grind a 3.615Mhz 10X for which I have found some old doner crystals if they are indeed old types and not just new crystals in old housings as many now are.

Pete
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Old 14th Jan 2019, 7:13 pm   #30
G6Tanuki
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Default Re: Xtal digital replacement

It's decades since I studied crystals but if you've 'thinned' the slab by a significant amount you will have affected the thickness:length and thickness;width ratios too, which depending on the original 'cut' of the Quartz will have some noticeable effect on Q and stability.
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