Looking for a 76.0khz crystal for FM encoder project - UK Vintage Radio Repair and Restoration Discussion Forum

jpdesroc · 2nd Feb 2018, 3:02 pm

Does anybody know where I could buy a 76khz crystal (or oscillator) ?
I already found 76.8khz values but I need a 76.0khz.
This will be used for a FM MPX encoder project.
This 76khz will be divided by two to generate 2 x 38khz
180deg out of phase signals..
Some 38khz crystals are available but still I need a 76khz.
Any new old stock distributors ??
Thanks
J-Pierre

ionburn · 2nd Feb 2018, 3:18 pm

Use a lower frequency and multiply up?

jpdesroc · 2nd Feb 2018, 3:54 pm

This will need some kind of phase lock loop circuit..
Easier to divide a higher frequency ? But I checked multiples of 76khz
and I did not find any value close enough to be divided to 76khz..
Thanks anyway for your reply.
Still searching..

G8HQP Dave · 2nd Feb 2018, 4:12 pm

Have you looked for 1900kHz or 3800kHz crystals?

Do you actually need a crystal? A carefully adjusted LC oscillator (perhaps on a harmonic, then divided) should be good enough.

jpdesroc · 2nd Feb 2018, 4:26 pm

I'm trying to clone part of the circuit of a Sencore SG-165.
The stereo MPX generator part.
Everything in this circuit is derivated from a 76khz crystal/oscillator.
Of course I could use an LC oscillator but it won't be rock solid
stable as a crystal..

G8HQP Dave · 3rd Feb 2018, 12:09 pm

Another option is a cheap DDS.

jimmc101 · 3rd Feb 2018, 2:23 pm

Maybe a 7.6MHz crystal and an PIC12F683 to generate 38kHz, inverted 38kHz and 19kHz all synchronous in one 8pin DIP. (Also has inhibit input for mono.)
I started this a couple of years ago and got as far as simulating the program (code attached) before deciding to use a
Si4713 to give me an integrated solution including RDS.

It would certainly replace an awful lot of circuitry on the MPX board, if you want originality then it would be simple to change the PIC to give 76kHz only and feed the output to TR202.
In either case the PIC requires a 5v supply, LM78L05 from 12v supply?
7.6MHz crystals are common, they are used in a lot of the cheap low power FM transmitters (BH1415F series based)>

Jim

2nd Feb 2018, 3:02 pm	#1
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Looking for a 76.0khz crystal for FM encoder project Does anybody know where I could buy a 76khz crystal (or oscillator) ? I already found 76.8khz values but I need a 76.0khz. This will be used for a FM MPX encoder project. This 76khz will be divided by two to generate 2 x 38khz 180deg out of phase signals.. Some 38khz crystals are available but still I need a 76khz. Any new old stock distributors ?? Thanks J-Pierre

2nd Feb 2018, 3:18 pm	#2
ionburn Heptode Join Date: Dec 2014 Location: Lincoln, Lincolnshire, UK. Posts: 583	Re: Looking for a 76.0khz crystal for FM encoder project Use a lower frequency and multiply up?

2nd Feb 2018, 3:54 pm	#3
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Re: Looking for a 76.0khz crystal for FM encoder project This will need some kind of phase lock loop circuit.. Easier to divide a higher frequency ? But I checked multiples of 76khz and I did not find any value close enough to be divided to 76khz.. Thanks anyway for your reply. Still searching..

2nd Feb 2018, 4:12 pm	#4
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Looking for a 76.0khz crystal for FM encoder project Have you looked for 1900kHz or 3800kHz crystals? Do you actually need a crystal? A carefully adjusted LC oscillator (perhaps on a harmonic, then divided) should be good enough. Last edited by G8HQP Dave; 2nd Feb 2018 at 4:20 pm. Reason: suggest LC

2nd Feb 2018, 4:26 pm	#5
jpdesroc Retired Dormant Member Join Date: Feb 2013 Location: Québec City, Québec, Canada Posts: 42	Re: Looking for a 76.0khz crystal for FM encoder project I'm trying to clone part of the circuit of a Sencore SG-165. The stereo MPX generator part. Everything in this circuit is derivated from a 76khz crystal/oscillator. Of course I could use an LC oscillator but it won't be rock solid stable as a crystal..

3rd Feb 2018, 12:09 pm	#6
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Looking for a 76.0khz crystal for FM encoder project Another option is a cheap DDS.