Grounding crystal casing?

sinus trouble · Post by **sinus trouble** » Tue Feb 07, 2017 1:04 am

Hello necks!
I have seen many circuits using crystals over the years and occasionally the crystal will have a soldered connection to ground?
in some cases I believe it is to support the body from mechanical shock or vibrations but does it serve any electrical or external influence preventative purposes?
Is it good practice to do as standard?

Maximus · Post by **Maximus** » Tue Feb 07, 2017 2:11 am

Yep it physically secures the crystal, which makes a difference. Also it tries to ground/shield the casing from rf that can feed back into ICs. Or something like that. I have some really old skool marine band transceivers which have crystals, and they're also grounded. Got the circuit diagrams some where.

Used to have the rejected PF1s from PYE Cambridge production belts that wouldn't resonate with the interchangeable for some reason.

That's another story though lol

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Albert H · Post by **Albert H** » Tue Feb 07, 2017 8:16 am

Maximus - you played with PF1s? That brings back some memories! I used to hacksaw off the IF and audio stages from the receiver, leaving the crystal multiplier and front end. I then used to use a ready-made IF strip that came out of a car radio - there was some firm in the Midlands who had thousands of these boards, and I bought a couple of hundred of them for about 75p each!

The transmitter end was slightly more of a challenge - I used to remove the crystal oscillator and the phase modulator, then add a little PLL board using an SP8629 (I think) and a MC145106. The output stage was modified to match into 75Ω, and the whole mess was put into a small aluminium box with a power supply, stereo limiter, and stereo coder.

The whole system used to work around 480 MHz, and used TV Yagis at both ends. I ran links over 20 miles (LOS) using this hacked technology! The PF1s used to cost £5 - 8 from Birkett's, and the rest of the gear wouldn't come to more than £20. I don't think that Gotts & Co. ever tracked one of these UHF links!

Maximus · Post by **Maximus** » Tue Feb 07, 2017 11:31 am

Ah yes, Birkett's isn't too far from here. I quite like getting a workout from walking up the hill.

Unfortunately, I used to get given the PF1s as a toy. It was my dad that worked for PYE. He was telling me the other day about someone that ordered the wrong transistors and a whole bunch of radios came off the assembly line with the transistors fitted back-to-front.

I can envisage Gotts' defeat from here haha

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Radio Garfield · Post by **Radio Garfield** » Tue Feb 07, 2017 11:34 am

There were situations in some RDVV where at its max power PLL lost lock and could not get locked again until you reduce RF power to certain level. Grounding both crystals solved that problem. You probably noticed on layout that there were thru holes for grounding those crystals.

Maximus · Post by **Maximus** » Tue Feb 07, 2017 11:46 am

Yes on the board here, it only has one crystal, as both the pll & pic ics share the same crystal. It has a solder pad to ground the casing.

I always fit the rdvv/pkbee exciters into a tin can enclosure to help shield from the rf. In some cases I've had to disconnect the LCD display to prevent feedback.

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sinus trouble · Post by **sinus trouble** » Wed Feb 08, 2017 12:30 am

Cheers people!

I have never noticed a significant difference grounded or not! Until it seems over time you get to know devices and start to notice tiny glitches?
I suppose any improvement however small is a bonus!