Crystals for the Central Electronics 10B

Now that the 10B is alive again after what was probably several decades I figured it was time to make some crystals for it the old fashioned way. Yes, I know what a VFO is, but that is not the point. I’m a sucker for the lost art of quartz crystals. There’s so much mystery and old wives tales around that that it has become some sort of dark art. In my limited experience its not magic, so long as you know your materials and keep in mind the laws of physics, and obey them.

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A “Better” Crystal Oscillator for the DL4YHF Frequency Counter

TL/DR: I like DL4YHF’s idea of making a frequency counter out of a microcontroller. I don’t like the Colpitts crystal oscillator that my Chinese clone added to it since it won’t work below 5 MHz very well. I made a better one with a 74HCU04 hex inverter an a couple extra parts.

That 400V bypass cap has delusions of grandeur.

In the last post we saw that the ever-popular “1 Hz to 50 MHz Frequency Counter and Crystal Tester” came up a bit short in the “crystal testing” department when it came to testing crystals in the low HF range (< 7 MHz or so). Now, if you really need a crystal oscillator and frequency counter for crystals in this range, I think there is a better way for the money and time, but if you already have one of these things and want it to work with lower frequency crystals, it might be worth doing something like the following. (H/T: ZL2PD had similar thoughts, though his clone has more power in the oscillator and probably does a little better at low frequencies out-of-the-box.)

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Thar be dragons! The Chinese 1Hz-50MHz “Crystal Checker” and why it spells trouble

The “1Hz-50MHz Crystal Counter Meter with Housing Kit” available various retailers. There are other versions of this kit in other colors that use the same circuit.

TL/DR: It is a poor and misleading circuit for testing crystals in the low HF region (~7 MHz and below). Relying on this device to screen old pressure-mounted rocks from the from the 40’s and 50’s will result in the discarding of many already hard-to-find good crystals. This post explains why.

It is billed as a DC-50 MHz frequency counter and crystal checker. The idea of a crystal oscillator coupled with a frequency counter is a good one–plug in an old crystal you got in the flea market and it will not only tell you if it is oscillating, but it will also tell you at what frequency it is oscillating. Some might question why you need to measure the frequency when its written on the case, but this is often not true when it comes to old amateur crystal holders or WWII surplus that was later modified; labels fall off, cases are switched, quartz blanks are reground, etc. Sometimes the case is empty or the crystal has been cracked. We often want to know if there is a good chance that a crystal will work in our gear, and the best test always seems to be in the equipment its intended for. That said, one can’t walk around the flea market with a BC-610 under his arm or take the case off a Viking II just to spot-check a crystal or two, so something like this for $10 and about an hour of your dexterous soldering skills is kinda handy.

Besides, kits are fun.

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