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 Post subject: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 3:01 pm 
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Joined: Dec Mon 17, 2012 5:09 pm
Posts: 41
Location: Quebec City, Canada G2E5S1
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


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 4:58 pm 
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jpdesroc wrote:
Some 38khz crystals are available but still I need a 76khz.
I didn't spot any 76 KHz crystals (saw the same 76.8 KHz you probably did), but there is an alternative.

Have you ever used an Exclusive OR or an Exclusive NOR gate as a frequency doubler? You can turn the 38 KHz into 76 KHz pulses then divide back down to 38 KHz with your two 180 degree out of phase signals.

If you don't come up with a 76 KHz crystal let me know and I will show you a circuit.

Curtis Eickerman

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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 5:06 pm 
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Joined: Dec Mon 17, 2012 5:09 pm
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Location: Quebec City, Canada G2E5S1
Eickerman wrote:
jpdesroc wrote:
Some 38khz crystals are available but still I need a 76khz.
I didn't spot any 76 KHz crystals (saw the same 76.8 KHz you probably did), but there is an alternative.

Have you ever used an Exclusive OR or an Exclusive NOR gate as a frequency doubler? You can turn the 38 KHz into 76 KHz pulses then divide back down to 38 KHz with your two 180 degree out of phase signals.

If you don't come up with a 76 KHz crystal let me know and I will show you a circuit.

Curtis Eickerman


Thanks Curtis,
I'd be happy to see your freq doubler circuit..
I think what you meant was this:
http://vhdlguru.blogspot.ca/2010/04/com ... plier.html
This could be my solution..
So far I found a 19.44Mhz oscillator I could divide by 256.
J-Pierre


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 5:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4907
Location: Rochester NY USA
I have used a CMOS 4060 oscillator / divider in the past for timing functions - there are other similar chips. 4060 has a crystal oscillator and 14 stage divider, each stage dividing by two, and outputs 4-14 each have a pin. So you could use a 2.432 MHZ or 4.864 MHz crystal and have outputs including 76 Hz, 38 KHz, 19 KHz, etc.


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 5:42 pm 
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Joined: Dec Mon 17, 2012 5:09 pm
Posts: 41
Location: Quebec City, Canada G2E5S1
Tom Bavis wrote:
I have used a CMOS 4060 oscillator / divider in the past for timing functions - there are other similar chips. 4060 has a crystal oscillator and 14 stage divider, each stage dividing by two, and outputs 4-14 each have a pin. So you could use a 2.432 MHZ or 4.864 MHz crystal and have outputs including 76 Hz, 38 KHz, 19 KHz, etc.


Since a 4.864 MHz crystal value is available the duo 4.864Mhz/4060 IC is my way to go !!
Thanks Tom.


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 6:39 pm 
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The 4060 is probably the way to go.

Alternative is to use either an Exclusive OR or Exclusive NOR gate of the same family as whatever logic you are going to use as the divider.

Then it is just a matter of using a small RC delay on one of the inputs and what you will get coming out is a pulse at each transition of the 38 KHz clock (needs to have square edges coming into the EXOR or EXNOR). This automatically gives you a synchronized 76 KHz but it is certainly not 50% duty cycle.

Then after you do your divide by 2 you are back at 38 KHz with your two out of phase signals from the flip flop.
Attachment:
Freq-Doubler.jpg
Freq-Doubler.jpg [ 23.17 KiB | Viewed 253 times ]
Curtis Eickerman

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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 6:45 pm 
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Joined: Dec Mon 17, 2012 5:09 pm
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Location: Quebec City, Canada G2E5S1
Thank you Curtis !


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 10:29 pm 
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Location: Somers, CT
How are you planning on phase locking the crystal to the stereo pilot?

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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Fri 02, 2018 10:58 pm 
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Joined: Dec Mon 17, 2012 5:09 pm
Posts: 41
Location: Quebec City, Canada G2E5S1
Peter Bertini wrote:
How are you planning on phase locking the crystal to the stereo pilot?


I'm gonna use part of the Sencore SG-165 Stereo Analyzer original design..
http://www.arcenson.com/public/Sencore_ ... ematic.pdf
From the start I needed a digital RF generator that would also do FM stereo multiplexing
for FM receiver repairs.. The only generators I found that would do that were
Sencore SG-165 and SG-80. The SG-80 was the best to check for but none could be found
to buy on the net. So After some browsing I finaly bought a nice calibrated Marconi 2022E
Synthesized RF generator with an external AM/FM modulation signal input.
So I will build the FM stereo encoder part of the SG-165 in a separate box
and use it with the Marconi. Doing so give me a very stable (frequency wise) generator
with both AM & FM stuff to use.
JP


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Sat 03, 2018 1:54 am 
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Ah, read too fast... I assumed you were building a decoder. Let everyone know how it works out.

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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Sat 03, 2018 3:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2108
Location: Saskatoon
You may want to check out this extremely simple stereo encoder project:
http://sm0vpo.altervista.org/audio/stereo_enc.htm


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 Post subject: Re: Looking for a 76.0khz crystal for FM encoder project
PostPosted: Feb Sat 03, 2018 7:05 pm 
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Joined: Dec Mon 17, 2012 5:09 pm
Posts: 41
Location: Quebec City, Canada G2E5S1
In the meanwhile I ordered this board:
http://electronics-diy.com/stereo_encoder.php

I don't know its reliability but will have to do some tests..
JP


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