Hack Your Crystal’s Frequency

[Drone] tipped us off about [Joachim]’s efforts to alter a crystal’s frequency. Through a process called penning, a crystal’s resonant frequency is lowered by painting the crystal with an indelible ink marker. Our curiosity piqued, we went off  and found more information about penning crystals. It turns out this technique has been around for nearly as long as there have been amateur radio operators. Outside of your local oscillator, and radio jammer, how might you best use a hacked crystal?

47 thoughts on “Hack Your Crystal’s Frequency

  1. Well, if you decide to acquire cheap surplus commercial or military equipment that may be “near” your desired band of operation… You may pen your crystals to get the desired frequency. One such application is for “Ham” or Amateur Radio operators, whose allocation spectrum space often butts right up to commercial space, to use this technique.

  2. a proper crystal may not be available at the time of need, or will take time to have shipped
    a variable capacitor would work if you built supporting circuitry for a VFO 9Variable Frequency Oscillator) but that would just replace a crystal rather than tweak it, and those circuits take space and can have a drift occur or a loss of frequency stability… they are nice to have, but crystals retain superiority


  3. > ignorant question…. Can’t you just buy another
    > crystal with the required frequency??? or may
    > alter it with a variable cap???

    Good question:
    1. Not every frequency value is available. Amateur frequencies are available from suppliers, but not every frequency, just the most common. And, you rarely find Amateur frequencies in ‘industrial’ crystals (like the usual 4Mhz, 16Mhz, etc. that you might run your Arduino or PIC from).
    2. You can custom order the frequency you want. There are number of manufacturers who’ll do this for you. But it’ll cost maybe US$15 to US$35 PER custom valued crystal.
    3. You can ‘swing’ a crystal with a variable capacitor, or a trim-cap, just not by much.

    Mike Y
    Dallas, Texas

  4. I would have loved to know about this hack in my red boxing days. I recall modifying a radio shack tone dialer with a new crystal to alter the frequency, but the exact frequency of crystal that would perfectly mimic quarter tones was very hard to find (if memory serves me it was 6.5536 Mhz). I had to opt for a commonly available 6.4900 Mhz crystal instead which worked, but not always well enough.

  5. I think one of the most obvious uses of this would/could be using a surplus crystal you have and tuning it to 60Hz or some multiple thereof to use for timing features. Sure there are plenty of ways to get a good clock signal but this would be a nice way to do it, or if you need two crystals to work together at certain frequencies each to get something of a “master” frequency penning would be a good idea so you can get as close to the signal as possible without ordering custom parts.

  6. @Juancubillo: Usually you can’t. Crystals that aren’t mass produced at common frequencies are often orders of magnitude more expensive, if available at all.

    Variable capacitors only allow you to bend the frequency so far (from what I’ve read, something on the order of a few kHz). You try and capacitively bend the crystal much more than that, and stability suffers.

  7. The reality of crystals as a frequency control device falls into another recurrent Engineering categorical. “Stable, Cheap, Repeatable, -pick any two”

    Oh, it’s quite “doable” to tweak crystals by chemical or mechanical alterations of the rock itself. With a consequent reality of those tweaks being inherently at major risk of instability or other failure modes. Same goes for external tweaks like resonance shifting by circuit element value variances. The basic operating principles of some technologies are to risk an almost pun- rock bound. There are some exceptions to solving the problem of not having a crystal on the desired exact frequency. PLL synths being the present day most commmon method. But there’s an intermediate technology trick that seems forgotten. Direct Multiplication/Division with up/down mixing can produce desired frequencies from stock crystals at “good enough” stability to cost ratios.

    Look at some CB radio circuits pre-PLL for details. and IIRC some Aviation radio systems made use of similar methods. The prime difference between switched crystal/multiplier circuits and a VFO is that stability to cost ratio. You “can” build TXCO oven style VFO etc devices and yes, a stable thermal box inherently does improve accuracy of all oscillators.

    After all the harsh realities are weighed though? The elegance of hacking a crystal by direct mechanical or chemical means lives in those applications where it really is “good enough” of a hack.

  8. basic rule of thumb for this method.

    Thicker – slower
    Thinner – faster

    Many a crystal radio set was moved in frequency by either sanding down (comet works well) or building up (pencil lead or solder work well).

    Don’t plan on moving it very far though.

    @oren: Harmonic modes are good for larger shifts, but are always going to be a multiple of the primary resonance. you can get the resonance out of the xtal itself or pick it out of an overdriven amplifier. W1GHZ uses this technique in his 902mhz,1.2ghz,2.3ghz and 3.4Ghz transverters to get the local oscillator frequency for example.

    As to the ‘get a new xtal’ suggestion, custom frequency crystals can be ordered but often take time to get and are often Not Cheap. iirc, the xtal for my 50mhz beacon (which needed to be @ 50,076,500hz +/- a few hz) was about $30 and took 4 weeks to get. Putting it in a xtal oven keeps it within a few hz, less xtal aging.

    Lest you think those last few digits are insignificant, when you start multiplying to get up into ghz range for microwave radios, it adds up. Multiply 50,076,500 by 50. Do the same for 50,076,550. The difference is 2.5Mhz. More than a whole FM radio band channel separation. Makes it hard to hear the other guy.

  9. When I was in college we got 2 radios from the airport that were used to communicate with planes; they accidentally left the original crystals in them for about a month before we accidentally told them about it, afterwhich they flipped out and a bunch of people over at the FCC or the airport or whatever got written-up.

    We could have been talking to airplanes; the frequencies of these crystals are not easily reproduced though, since we’re talking about super precise secret frequencies.

  10. Thnkz for the answers. I was under the impression xtals had lots of values or could be tweaked to any desireable one. And I also had no idea you could order custom ones… for a price of course.
    Thnkz again all who replied.

  11. To answer Devlin’s question. Even though I am an amateur radio Operator, I don’t know what I’d modify a crystal for, or even if I would even ever do it. I could see myself doing it to bring an old rock bound station to life operating, exclusively on a net frequency. In tat case the process is made easier in that many of the older stuff used crystal sockets for crystal holders that where made to come apart for easy access to the crystal. Otherwise I’d spend the money to have a custom crystal prepared, because it wouldn’t be something I’d need to do often, or rarely. Other than applications where the crystals can be mass produced inexpensively, crystal control is reserve for applications where accuracy, and stability is required over a wide range of changing operating conditions. IMO in such application money spent for a custom crystal, is money well spent, and may be the responsible thing to do, to do all I can to prevent interference to others.

  12. This would be useful for people who have simple crystal-bound transmitters or receivers (i.e., http://www.kenneke.com/~jon/pixie/ ) who want to be able to hop around a radio band more so than can be provided by a variable capacitor alone.

    CAN SOMEONE TELL ME in a single sentence why this works? (I don’t want to read a million pages.) It seems like adding/removing electrically-conducting material is just a more dramatic way to alter capacitance, but I’m sure there’s more to it than that…

  13. Sounds similar to the operation of a deposition rate monitor.

    The only difference is that a rate monitor measures the change in frequency to determine the amount of material applied

  14. @Scott very simplified in one line: More weight means slower vibration. Slower vibration equals lower frequency.
    In a range, of course. And it doesn’t even has to be a conucting material.

    After all, that’s what xtals do, vibrate. Then there’s the piezoelectric effect, electrical models, equivalent impedance, and a lto of stuff about it, but it all comes down to the thing vibrating at it’s resonant frequency.

  15. @Scott: you’re adding (or removing, as stated in other comments) mass, which changes the frequency of oscillation; like changing the mass (or length) of a clock’s pendulum. It’s probably better to use something that doesn’t conduct electricity, if you can get it (solder is probably used for density, but most of the denser things also conduct: lead, gold, etc.).

  16. @terry: My Grandfather used to do it when he was a teenager and into Ham radio. It’s older than your dad’s dad.

    Honesty if people would dig into older information stores (ARRL handbooks) instead of only the hipster trendy places they would learn more of these old tricks.

    for every cool trick someone discovers, there are another 80,000 that are better and more than 20 years old. The old farts know way, way more than any college age kid.

  17. P.S. Crystal control is no more accurate than a PLL digitally tuned radio.

    The way you prevent interference is to use the PROPER radio design proper feedline, proper antenna.

    If your radio is garbage and has a lot of sideband lobes, then you buy cans to filter them out. if your antenna is not tuned dead on it causes interference. Amplifiers that are designed poorly cause band splatter.

    I have a digital rig that will outperform ANY crystal rig out there in signal cleanliness and stability.

    That said, I can build 50,000 good crystal QRP rigs for the price of this one Icom…

    1:1 match No impedance nodes in your feedline, clean and properly tuned amp, clean and properly designed transmitter exciter. THAT is how you prevent interference.

    Xtals have nothing to do with it.

  18. @fartface – “Crystal control is no more accurate than a PLL digitally tuned radio”

    “Phase jitter” is a problem that arises in the PLL (divider) itself, not from its tach or reference signal which is usually (Ham, CB, Avionics) sourced from a crystal.

    A PLL can only be as good as the signal it locks to.

    In the days when crystals were square and supported between two plates with raised lands at each corner, in openable carriers, it was possible to run a screw through the side to change the clamping pressure on the plates and produce a VXO – Variable Crystal Oscillator, but still only over a very limited range.

  19. @fartface said: “if your antenna is not tuned dead on it causes interference”


    Since when do you have to have a resonant antenna to transmit a clean signal?

    Resonance is nice, but not necessary. If it was, it wouldn’t have multi-band dipoles like the g5rv

  20. I remember using a similar crystal to overclock a 386 sx. I cant remeber the frequency I achieved over the one it was already working, but I remeber feeling pretty awesome about it. I may still have this motherboard around :)

  21. what about Q of opened and tuned crystal?
    I don’t know about MHz range crystals, but common 32768Hz clock crystals show very significant fall of resonance amplitude if air is let into can.

  22. hm..

    I read somewhere that the crystals used for ultra-precise applications (i.e. OCXOs) are inert gas filled for this reason.

    it makes me wonder if you could tune a crystal by changing the pressure in the can (solder blob + small heater, same as sealing Geiger tubes)….

  23. @ people who responded

    Yeah, I’m not a huge aircraft OR radio person, but I’m sure it’s not such a big deal these days. All I know is that there is equipment out there that uses extremely precise crystals that you can’t easily obtain; whether it’s because of the cost making it or if it’s a frequency that the FCC thugs don’t want you chatting on is something I never looked into that much.

  24. Hacking 32768 Hz 3×8 mm crystal (watch crystal):
    To open it you can spin it in electric
    drill to make a groove in the base
    and then use cutters to snap the base
    out of the can.
    After opening frequency goes down 10-30Hz.
    Wafer is U shaped like “tuning fork” and
    soldered at the root of U.
    To increase the frequency you can gently
    grind off tips of both branches of U simultaneosly with fine
    sand paper. If you grind off about 1mm frequency
    goes up to about 60KHz.
    If you grind off unsymetrical one branch more
    than the other you ruin the Q of the crystal.

  25. A crystals frequency is easily moved by varying the spring pressure of the holder. I made such a device earlier last year and use it on my 80 meter rig (bare essential tx 50L6. I used a Bliley crystal for the project because I had one but one could make a holder from anything, hardwid even. Thereare pictures of my device on the AWA mail list gallery. It works perfectly giving one enuf wiggle room to avoid QRMing anyone. I also tied it n conjunction with my VXO circuit using a trimmer. the combo gives even more wiggle room.

  26. I have a couple of clocks that both have RTC and uses the standard 32,768Hz cylindrical crystals. One (a battery operated LCD type) goes late by about 1 minute per month while the other (line powered 4-inch LED type that we built) runs 1 minute/month too fast. I exchanged their crystals thinking that the error will transfer but it didn’t work. The LCD type still runs late so I concluded that something in the circuit affects the clock frequency, not the the crystals themselves. Any idea? Thanks.

    1. Same here. Found that in my case it was oxidized capacitors causing the issue and replacing them solved it. Also a parallek series resistor works to make the temperature meter on many clocks work properly

  27. This technique can be very useful when utilizing a home built QRP (very low power 5 watts or less) transmitter/transceiver that is rock bound by the crystal’s designed frequency. Add weight or remove it to change the frequency (albeit not by a whole lot) may make the difference for one QRP Op to be able to zero beat with another or make that supply contact using CW (morse code). Think middle of nowhere Alaska or Canada where ordering a specific crystal is not much of an option during the winter.

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