How we measured frequency - Inside an old crystal calibrator

Continuing on our old test equipment series, today I describe an old crystal calibrator. This was used to ensure that receivers with free-running oscillators and analogue dials were on frequency. The calibrator was calibrated using WWV / WWVH on 5, 10 or 15 MHz as a frequency reference.
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[@FishingHam]

Another awesome video Peter!

[@tdumnxy]

Another very interesting video.

[@jayroland9481]

I have a vintage Trio JR60 valved set with built in xtl calibrator but not a clue how to use it :-(

[@WI9LL]

Were you pointing at parts of the circuit with a blade of grass? Tree this is why I love this channel. Ham radio with bananas, beaches, and blades of grass...

[@researchandbuild1751]

It was an adjustment tool

[@WI9LL]

Hey, I have a handful of 12Mhz crystals. 5 to be exact. Any ideas for a circuit I can build with any or all of them?

[@vk3ye]

Use 4 crystals in a crystal filter, one for the carrier oscillator and build an SSB transciever for 7 MHz. Use the circuit at www.phonestack.com/farhan/bitx.html as a starting point with a DDS or VFO on 5 MHz.

[@noisyaudio]

How is this device itself calibrated?

[@JohnTarbox]

Generally we would zero beat it against a known radio station such as WWV. This is covered in the video.

[@joshmyer9]

John Tarbox To clarify one thing not explained, for newer folks: you are not generally zero beating the main signal out of the calibrator, but instead, one of its harmonics. Since there’s not any real output filters, there should be pretty strong harmonic signals to work with. As a bonus, you get even better resolution/precision this way: 10MHz is the 10th harmonic of 1MHz, so a 1Hz beat frequency actually gets your oscillator to within 0.1Hz of 1MHz! (I was kind of surprised to see an 8MHz harmonic of 4 MHz, since iirc these ICs should be putting out square waves, which only have odd harmonics. I’d guess 4MHz is pushing the IC so fast that it gets mangled into more of a triangle wave.)

[@guillermosempron5776]

Circuit?

[@KennethNicholson1972]

draw one for us.

[@vk3ye]

Unfortunately it's lost. But there are many here: www.google.com.au/search?q=crystal+calibrator+circuit&rlz=1C1GGRV_enAU751AU751&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjV-p_XrevZAhUL9GMKHRI3Aw0Q_AUICigB&biw=1280&bih=633

[@flexairz]

How about reverse engineering?