Crystal checker

[Gerry Santos]

Anybody have a simple home made crystal checker diagram that will work for any frequency? Search the forum but to no avail.

Thanks.

[Bruce Abbott]

Two Simple Crystal Test Circuits (http://english.cxem.net/izmer/measured38.php)

[ArtU]

Here is one with a PCB layout

http://www.diy-electronic-projects.com/p218-Crystal-Tester

[rick.benjamin]

Three circuits here
http://www.uoguelph.ca/~antoon/circ/circuits.htm

[Gerry Santos]

Wow...that's plenty! Thanks guys! :D

[vintage1]

Be aware that whilst they may check that it is i fact oscillating, they don't check to see if its oscillating at the correct frequency.

Best for that is a transmitter and a frequency counter. For TX Xtals, and an RX and counter for RX circuits.

[lazy-b]

Gerry, Yes.....whats important is checking its frequency drifting......I have 5 locally made Crystal, it works perfectly for 5 years....then suddenly one of my Helicopter was crashed due to frequency drifting.......now, I replace all those locally made Crystal with Commercial Grade Crystal manufacture by HITECH, I guess, more than 10 years has pass.....the receivers works perfectly.

Another problem is Intermittent working crystal......sometimes it works perfectly on the ground but it suddenly not working due to vibration.

I guess, its better to shift to 2.4 GHZ.

[Trevor_G]

There is a problem here that has not been mentioned. All crystals are not the same. They have different cuts and are manufactured to work with different load capacitances.

An example of the problems this can cause. I have a number of Futaba Xtals that have always worked fine with my Futaba Rx's and a Hitec Feather. A few years ago I bought some Webra Rx's. Most of the Xtals worked fine but some gave reduced range and one refused to work at all.

Never did find out what the cause was. It could have been a capacitance problem or possibly some Xtals had a low Q and needed a bit more drive.

All this is compounded by the fact that RC Xtals are 3rd overtone. While I have never seen one oscillate on the wrong overtone it is certainly possible.

[vintage1]

Not all xtals are third overtone, and in tramnsmitters at least, you have

- which overtone they expect to use
- whether or not explicit frequency multiplication is used post the oscillator to get to the power stage.
- what loading - resistive and capacitive - they are cut for.
- what their FM capability, in MHZ per pf is..
- What their temp coefficient, in PPM per deg C, is.

That's too many variables for me to ever contemplate using somebody else's (brand) Xtal in a transmitter.

[Bruce Abbott]

Never assume anything. I have a couple of 'cheap&nasty' 40MHz receivers that run a 20MHz crystal in fundamental mode, then expect the mixer to work on its second harmonic!

I also have a collection of brand new crystals that won't work in some receivers due to low Q. Of course they all work fine on the crystal tester. :mad: