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I'm working on my Heathkit HR-1680 receiver and I have a crystal that I suspect is bad. Can a NANO VNA be used to test a crystal? If so, how?

Thanks and 73,

Justin B.
KI5GKD

I use mine often to check crystals when I suspect they may be bad. I have
some SMA to alligator clip cables which make it easy. You can over the
expected frequency range, and you should see a S11 return loss dip and
phase shift around the resonant frequency.

Also check out this video:

--
Rob Campbell
KG6HUM


On Fri, Sep 8, 2023, 8:54 PM Justin Bowser - KI5GKD <
justin.bowser@...> wrote:

I'm working on my Heathkit HR-1680 receiver and I have a crystal that I
suspect is bad. Can a NANO VNA be used to test a crystal? If so, how?

Thanks and 73,

Justin B.
KI5GKD

Thanks, Rob. Do I need to use both channels or just the "primary?"

73,

Justin B.
KI5GKD

Justin,

Either should work for just seeing if the crystal has a resonance near the
expected frequency. I've just used channel 0 for S11 measurements, with
the coax shield to one side of the crystal and the center conductor to the
other side.

In that video he's calculating the various parameters of the crystal using
through S21 measurements going out of channel 0 and into channel 1.

If you have a known good crystal, I'd suggest trying it on that first, so
you know you have your settings correct and know what to expect. You may
need to adjust your frequency range and vertical range for the readings.

--
Rob Campbell
KG6HUM

On Fri, Sep 8, 2023, 10:44 PM Justin Bowser - KI5GKD <
justin.bowser@...> wrote:

Thanks, Rob. Do I need to use both channels or just the "primary?"

73,

Justin B.
KI5GKD

Rob,

Thanks for the info. I've got a few crystals laying around and I'm basically just looking for a go/no-go on the crystal as it appears dead in circuit. I'll watch the video in the morning, too tired to concentrate on it right now!

73,

Justin B.
KI5GKD

The basic go no go test as described is fine. However if you want to accurately determine the crystal parameters you will need more work. For HF crystals a good test jig to avoid strays is useful. Also at resonance the crystal is a series tuned circuit with very very low loss resistance R. This is not a good match to the nano vna which is 50 ohms. There will be both phase and frequency shifts as well. Unraveling all these for the crystal parameters is a challenge.

What the VNA will not do is tell if a given crystal will oscillate, cleanly and on frequency, in a particular circuit, which is what the OP wants.
73, Don N2VGU

I have tested and sorted quite a few crystals using a specialy designd adapter for the NanoVNA.

See:

Wow I'm impressed, what a website everything you wanted to know about testing crystals. Thank you Lex.

Man, that is some heavy stuff!

Justin B.