Regrinding crystals to increase frequency slightly

[mikeselectricstuff]

I have an application which will need 10 or so 49.9MHz crystals (HC49 can) The nearest off-the shelf value is 49.86, about 800ppm low
Has anyone tried regrinding crystals to tweak the value slightly?

(I know about programmable oscillators, but this needs to be a clean sinewave, so a programmable osc would need additional filtering)

[CaptDon]

How critical is the frequency? In ham radio use years ago we could raise them a tiny bit by using toothpaste and a flat sheet of glass. Downside, they become hard to start in many oscillator circuits and you lose stability. Buy some of the ones that are 800hz off and maybe with component selection you can successfully 'pull' them with a trimmer capacitor. Try a series resonant or parallel resonant circuit. 800hz isn't far at 49mhz. I think the manufacturers tolerance is wider than your 800hz differential anyway. What is the chances some of those crystals may be dead on as supplied?? I suspect your crystals may drift several hundred hertz with temperature change alone. Again, how critical is frequency tolerance??? You may be sadly disappointed unless you go to temperature controlled circuits and enclosures.

 

[nali]

UK-based Quartzlab used to be good for one-off or oddball requirements, I used them ages ago for convereting PMR radios into ham, but looks like they've just packed it in a few months ago. No idea what Klove are like for MoQ etc:

https://www.klove.nl/quartslab/

Dear visitor,

Unfortunately, Mid 2021 Quartslab decided to stop its activities.

Since Klove Electronics has been manufacturing the Quartslab crystals for several years now.

The logical step was having Klove electronics take over all Quartslab activities within the quartz crystal business.

If you stumbled upon Quartslab for the first time looking for quartz crystal services, you are at the correct “new” place. So don’t hesitate to send us an RFQ or your order….

[spaceballs]

Oh should make youtube video, and use an laser to change the freq!

[dmendesf]

Try heating it to reach the desired frequency. If it works you can make a very simple OCXO to maintain temp:

https://www.romanblack.com/xoven.htm

[wraper]

Adjusting frequency by electrolysis of electrode silver plating https://zen.yandex.ru/media/elektroradio/kak-izmenit-chastotu-kvarcevogo-rezonatora-5e5ccb7d23f6716bacbc3ff4
Place a silver electrode into a water filled crystal can and pass the current. 7 seconds allowed to change the frequency by 15 kHz.

[Terry Bites]

Abracon may make just the thing; 49.9MHz with selectable tempco options.

Yop can use HF, 3% will do apparently. Have the antidode and spare eyeball ready.
https://www.sja.org.uk/first-aid-supplies/first-aid-supplies-and-consumables/ice-packs-and-heating-pads/pain-relief-sprays/calcium-gluconate-gel-40g/

https://acleaningproduct.co.uk/product/whink-products-1291-rust-stain-remover-16oz/
Or ask your local dental technican for a bit.
 
https://www.ebay.co.uk/itm/203601264655?hash=item2f6794c00f:g:YrIAAOSwXKhgdYSi, 
Or finegrit sandpaper

[mikeselectricstuff]

UK-based Quartzlab used to be good for one-off or oddball requirements, I used them ages ago for convereting PMR radios into ham, but looks like they've just packed it in a few months ago. No idea what Klove are like for MoQ etc:

https://www.klove.nl/quartslab/

Dear visitor,

Unfortunately, Mid 2021 Quartslab decided to stop its activities.

Since Klove Electronics has been manufacturing the Quartslab crystals for several years now.

The logical step was having Klove electronics take over all Quartslab activities within the quartz crystal business.

If you stumbled upon Quartslab for the first time looking for quartz crystal services, you are at the correct “new” place. So don’t hesitate to send us an RFQ or your order….

FYI Klove quoted EU25 each + 15 UK shipping, 8 week leadtime

[mikeselectricstuff]

Just had a quote from http://www.krystaly.cz/en/  - 6 Euros each , 4 week leatime. 

[m3vuv]

ive used a pecil or marker pen a few times to decrease the frequency but found you cant go too far as mentioned before oscillation stops,i have a few lasers tho,just wondering if blasting themwith a 2 watt laser  would remove enough material to raise them?,never tied it but its a thought.

[Doctorandus_P]

Another option is to synthesize your frequency with some standard crystal and a DDS chip.

[EPAIII]

When I saw the word "sandpaper", I thought it would have been used to decrease the size of the crystal itself instead of reducing the mass of the electrodes plated on that crystal. And, after seeing the video where the sealed crystal can was sawed open and it was the plated side electrodes that were sandpapered, I still wonder if perhaps a diamond grit could be used to remove part of the crystal material at the top where there was a flat on the circumference of the round disk.

In fact, I wonder if perhaps that is how the factory tuned the crystals to a final value before the cans were sealed. I have to wonder if anyone else may have thought this would work if a higher frequency was wanted.

That would have raised the frequency which was what the OP wanted. But I wonder if you needed to decrease the frequency,  perhaps there may be a way to chemically deposit more metal on those electrodes to increase their mass, thus lowering the frequency.

[BrianHG]

Use this guy with any crystal value: CDCE925PWR from TI.

https://www.arrow.com/en/products/cdce925pwr/texas-instruments

It has an EEPROM, so once you set it, it will power up in that frequency every time, though it still supports in-system dynamic programming as well as holding 2 configurations in the EEPROM which can be switched via 1 digital input pin.

It also has a 'TUNING' voltage input so you may tune the source crystal.  I used this guy for 'genlocking' a home made graphics video output card onto a source video signal.

You can also software I2C set that tuning input pin to internal mode and tune the crystal meaning no need for a varicap if you want a dead perfect frequency.

It has multiple programmable frequency outputs.

[mikeselectricstuff]

Another quote - Euroquartz GB£6.12 each., 8 week leadtime.  Surprisingly cheap for a UK place

[Dave]

Out of curiosity, what is is that you're doing that requires an exact 49.9 MHz crystal?

[mikeselectricstuff]

Out of curiosity, what is is that you're doing that requires an exact 49.9 MHz crystal?

Short-range radio transmitter - this was originally an art project where people walk round an area with receivers, and hear the voices of past residents. The original hardware was built about 18 years ago, with the audio stored on a board full of EPROMS and HCMOS.
I'm building a few new units to replace some which have been lost or damaged over the years.