#29760

This is a continuation of a side-topic from the "SR2000 initial power up" thread.

I use a crystal tester for 2 purposes: 1 is to find the approximate frequency at which the crystal will probably oscillate in an application circuit.? 2 is to provide a reference when experimenting with the crystal itself.? Does baking a crystal affect its resonant frequency?? How far did it move when I added some ink to its surface?
My frequency counter's time base is far more accurate than needed for the current project.? At 16 MHz, it's giving a count that's less than 10 Hz away from my more-accurate way of measuring frequency.
Which is... my Drake R8B receiver that I've outfitted with a TCXO for its reference oscillator.? I set it to USB mode, tune 500 Hz below where I expect the frequency is, and run a scrap of wire from its antenna jack to about 10 cm away from the oscillator I wish to measure.? Spectrum Lab runs on my laptop next to the R8B.? It shows the frequency of the beat tone.? I add that to the R8B's dial setting to obtain the frequency I'm listening to.? Nowadays, the WWV carrier comes in a few Hz away from where I expect it.? When I start to care for more accuracy, I tweak the TCXO's voltage control input.
I find the receiver to be a more convenient instrument for measuring an oscillator's frequency.? I don't have to hold a probe, and I don't have to consider whether the presence of the probe is perturbing the oscillator.? It does have its drawbacks, though.? I might be measuring a spur, not the strongest oscillation, and not know it.? Also, I have to know within about 5 kHz of where the frequency will be; tuning slowly over a larger range than this is more tedious than hooking up the frequency counter probe.
If I ever need sub-Hz accuracy on the frequency counter or the receiver, I'll rig up a rubidium oscillator via a CY22801 to provide the time base needed.
My present goal with regards to the SX-117 is to get all my crystal oscillators running within 500 Hz of where they ought to be.? I don't see any purpose of getting them any better than the range of VFO drift.? Fortunately, there are trimmers in the radio that can pull them up or down at least that much.? The 1.7 and 1.6 MHz BFO oscillators don't have trimmers but they're now at?1600013 and 1699979 respectively according to the R8B. ? It seems that one compensates for drift in these by setting the BFO frequency.
Cheers,
Halden VE7UTS

#29763

开云体育

Halden, you are perhaps replying to posts by me and then Jim.

You have answered some of my lingering questions ..thank you!

It seems to me that old Xtal testers were meant to see it is any good at all.. activity, but I suppose now they also have? frequency readouts to many digits.? Since you have been into these, have you found that the “in radio” frequency is the same as the “in your tester” frequency?

Back in the 1960 era before we had all this accuracy we could not measure it, so it hardly mattered, but now this stuff can be measured, so we wonder ..? about things like Walt’s suggestion.

?

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From: [email protected] [mailto:[email protected]] On Behalf Of HF via groups.io
Sent: Sunday, March 31, 2024 6:12 PM
To: [email protected]
Subject: [HallicraftersRadios] Crystal testing and frequency measurement

?

This is a continuation of a side-topic from the "SR2000 initial power up" thread.

I use a crystal tester for 2 purposes: 1 is to find the approximate frequency at which the crystal will probably oscillate in an application circuit.? 2 is to provide a reference when experimenting with the crystal itself.? Does baking a crystal affect its resonant frequency?? How far did it move when I added some ink to its surface?
My frequency counter's time base is far more accurate than needed for the current project.? At 16 MHz, it's giving a count that's less than 10 Hz away from my more-accurate way of measuring frequency.
Which is... my Drake R8B receiver that I've outfitted with a TCXO for its reference oscillator.? I set it to USB mode, tune 500 Hz below where I expect the frequency is, and run a scrap of wire from its antenna jack to about 10 cm away from the oscillator I wish to measure.? Spectrum Lab runs on my laptop next to the R8B.? It shows the frequency of the beat tone.? I add that to the R8B's dial setting to obtain the frequency I'm listening to.? Nowadays, the WWV carrier comes in a few Hz away from where I expect it.? When I start to care for more accuracy, I tweak the TCXO's voltage control input.
I find the receiver to be a more convenient instrument for measuring an oscillator's frequency.? I don't have to hold a probe, and I don't have to consider whether the presence of the probe is perturbing the oscillator.? It does have its drawbacks, though.? I might be measuring a spur, not the strongest oscillation, and not know it.? Also, I have to know within about 5 kHz of where the frequency will be; tuning slowly over a larger range than this is more tedious than hooking up the frequency counter probe.
If I ever need sub-Hz accuracy on the frequency counter or the receiver, I'll rig up a rubidium oscillator via a CY22801 to provide the time base needed.
My present goal with regards to the SX-117 is to get all my crystal oscillators running within 500 Hz of where they ought to be.? I don't see any purpose of getting them any better than the range of VFO drift.? Fortunately, there are trimmers in the radio that can pull them up or down at least that much.? The 1.7 and 1.6 MHz BFO oscillators don't have trimmers but they're now at?1600013 and 1699979 respectively according to the R8B. ? It seems that one compensates for drift in these by setting the BFO frequency.
Cheers,
Halden VE7UTS

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don??? va3drl

#29765

Hi Don,
I don't know anything about old Xtal testers.? My crystal tester is a 2N3904, a few capacitors and resistors, and a $13 frequency counter module similar to what ebay offers in response to the search term "Frequency Measurement Module".? It's about 2 days old.?
In-radio frequency is always different from in-tester frequency.? In most cases, the difference is less than 3 kHz, but it could be a little more if the circuit is configured for series resonance and the tester is for parallel. Application circuits generally have an adjustable inductor or capacitor to fine tune the oscillation frequency.? My tester doesn't.
It can also be a lot different!? Most crystals marked in the 30s, 40s, and 50s of MHz oscillate near 1/3 of their marked frequency in the tester.? This doesn't surprise me because it's common for "overtone" crystals to be used at these frequencies.? What surprised me was one crystal marked in the 20s of MHz that oscillated near 3* the marked frequency.? Some crystals in the 1 and 2 MHz ranges oscillate near 3 times the marked frequency in the tester, too.
I wasn't aware of ham radio in the 60s, but in the late 70s, the notion of a VFO with the stability of a crystal sounded really cool.? I tried to build a frequency synthesizer for use with my Johnson Ultracom I had converted to 2m use.? Nowadays, for some reason, I want TCXO-like stability.? But not for the HT-37, HT-44, SR-150, or SX-117.? Maybe for the HT-40 some day.
Cheers,
Halden