Regrinding crystals to increase frequency slightly - Page 1
Forum section: electronics / projects

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 06, 2021, 01:35:33 am
content: 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 lowHas 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)

author: CaptDon
author_rank: Super Contributor
timestamp: December 06, 2021, 01:55:42 am
content: 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.

author: nali
author_rank: Frequent Contributor
timestamp: December 06, 2021, 10:07:09 am
content: 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/Quote

author: spaceballs
author_rank: Newbie
timestamp: December 06, 2021, 03:08:15 pm
content: Oh should make youtube video, and use an laser to change the freq!

author: dmendesf
author_rank: Frequent Contributor
timestamp: December 06, 2021, 03:18:21 pm
content: 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

author: wraper
author_rank: Unknown
timestamp: December 06, 2021, 03:42:22 pm
content: Adjusting frequency by electrolysis of electrode silver platinghttps://zen.yandex.ru/media/elektroradio/kak-izmenit-chastotu-kvarcevogo-rezonatora-5e5ccb7d23f6716bacbc3ff4Place a silver electrode into a water filled crystal can and pass the current. 7 seconds allowed to change the frequency by 15 kHz.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 06, 2021, 05:17:56 pm
content: 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

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 07, 2021, 03:11:45 pm
content: Quote from: nali on December 06, 2021, 10:07:09 amFYI Klove quoted EU25 each + 15 UK shipping, 8 week leadtime

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 15, 2021, 03:44:41 pm
content: Just had a quote fromhttp://www.krystaly.cz/en/- 6 Euros each , 4 week leatime.

author: m3vuv
author_rank: Super Contributor
timestamp: December 15, 2021, 05:28:14 pm
content: 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.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: December 16, 2021, 07:18:32 pm
content: Another option is to synthesize your frequency with some standard crystal and a DDS chip.

author: EPAIII
author_rank: Super Contributor
timestamp: December 20, 2021, 08:19:06 am
content: 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.

author: BrianHG
author_rank: Super Contributor
timestamp: December 20, 2021, 09:35:07 am
content: Use this guy with any crystal value: CDCE925PWR from TI.https://www.arrow.com/en/products/cdce925pwr/texas-instrumentsIt 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.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 21, 2021, 04:30:29 pm
content: Another quote - Euroquartz GB£6.12 each., 8 week leadtime. Surprisingly cheap for a UK place

author: Dave
author_rank: Super Contributor
timestamp: December 22, 2021, 07:18:58 am
content: Out of curiosity, what is is that you're doing that requires an exact 49.9 MHz crystal?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 22, 2021, 10:41:27 am
content: Quote from: Dave on December 22, 2021, 07:18:58 amShort-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.