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Crystal alternative

Posted: Tue Sep 04, 2018 9:55 am
by RodeoJack
Has anyone found a working alternative for the traditional rock?

I have a ND-1 that I need to shift a bit. Now that National is gone, Nautel doesn't appear to have an alternative ... at least nothing I can get anytime soon.

If there's anything that's already built and (more or less) useable for this application, I'd prefer that, as I have a bit of a time crunch on this project.

Re: Crystal alternative

Posted: Tue Sep 04, 2018 11:52 am
by COMMENG
What is the required holder/mounting and is this a parallel resonant or series resonant crystal circuit?


I posted one such potential solution here:

viewtopic.php?f=2&t=6345

Some crystals can still be had from:

http://www.af4k.com/crystals.htm

Another solution is to take a DDS and amplify the voltage. (Accuracy is better).

http://www.analog.com/en/analog-dialogu ... ently.html

http://www.analog.com/media/en/training ... MT-085.pdf

This guy sells DDS':





COMMENG

Re: Crystal alternative

Posted: Tue Sep 04, 2018 11:56 am
by Shane
Try here:
https://www.iqdfrequencyproducts.com/pr ... tz-crystal
As far as I looked they have crystals down to 1.84 MHz.

Re: Crystal alternative

Posted: Tue Sep 04, 2018 10:21 pm
by Deep Thought
I'm working on a synthesized, GPS-disciplined replacement that would attach to the transmitter via its AM stereo exciter input jack, but due to real life getting in the way it is several months from market.

Re: Crystal alternative

Posted: Thu Sep 06, 2018 10:27 pm
by jthorusen
Greetings to the Forum:

Beware DDS - phase noise. I would think an old-fashioned PLL would be better.

Regards,

Re: Crystal alternative

Posted: Fri Sep 07, 2018 10:31 pm
by Deep Thought
The device I am using has very low phase noise, which is what makes it usable for this.

Re: Crystal alternative

Posted: Tue Sep 11, 2018 1:18 pm
by REW
Micheal Paton from Baton Rouge, La. had a device for some of the Harris AM transmitters. I think he said it could be set via dip switch to output a frequency of .5 to 5Mhz. I saw the board he had at the Alabama Broadcasters Association convention and it looked professionally made and the price wasn't bad.

Re: Crystal alternative

Posted: Wed Sep 12, 2018 2:05 pm
by COMMENG
REW wrote:
Tue Sep 11, 2018 1:18 pm
Micheal Paton from Baton Rouge, La. had a device for some of the Harris AM transmitters. I think he said it could be set via dip switch to output a frequency of .5 to 5Mhz. I saw the board he had at the Alabama Broadcasters Association convention and it looked professionally made and the price wasn't bad.

For $850.00 I think I'll wait for DT's (hopefully lower cost) module.


COMMENG

Re: Crystal alternative

Posted: Wed Sep 12, 2018 9:59 pm
by ChuckG
I used a Delta RG1 to replace a failed crystal oscillator in a BC1T until a replacement could be found. Worked surprisingly well.

Anyone making retrofits for other xtal controlled equipment, like Marti STL gear? Or are those dead in the water when the need arises?

Re: Crystal alternative

Posted: Thu Sep 13, 2018 5:26 am
by kcbooboo
There's a very inexpensive synthesizer / oscillator called the ProgRock, available at qrp-labs.com. It can use a TCXO as a reference for stability of a few parts per million. It covers a range of around 3 kHz to almost 300 MHz. Puts out a 3V square wave. There are actually three separately programmable individual outputs. The only downside to the device is that it can't be used in a true-FM situation where modulation must be applied to the oscillator, since there's no input for that with the TCXO. The raw crystal (stock) might be able to be modulated if one added a varactor circuit to the device. I was planning on using one of these to replace crystals on a 29 MHz FM base station that (fortunately) uses Phase Modulation and doesn't need the oscillator to be modulated.

There's also an ovenized reference module available for this unit. There's even an inexpensive GPS receiver option that unfortunately won't continuously correct the ProgRock in real time.

With a suitable amplifier and some sort of filtering, this device should be stable enough (+/- 20 Hz) to work with some AM broadcast transmitters.

Bob M.

Re: Crystal alternative

Posted: Thu Sep 13, 2018 10:52 am
by Deep Thought
kcbooboo wrote:
Thu Sep 13, 2018 5:26 am
There's a very inexpensive synthesizer / oscillator called the ProgRock,
That's the one I'm using with some outboard interface electronics. It can be GPS-disciplined and once the parameters are stored in NVRAM it is very stable.

Re: Crystal alternative

Posted: Thu Sep 13, 2018 1:48 pm
by RodeoJack
Interesting.

Might have to add further division though. I need 2960 kHz in a "divide by two" application.

... unless the Nautel would allow the "divide-by-four", which they use at lower frequencies, to work.

Maybe?...

Re: Crystal alternative

Posted: Thu Sep 13, 2018 3:58 pm
by REW
COMMENG wrote:
Wed Sep 12, 2018 2:05 pm
REW wrote:
Tue Sep 11, 2018 1:18 pm
Micheal Paton from Baton Rouge, La. had a device for some of the Harris AM transmitters. I think he said it could be set via dip switch to output a frequency of .5 to 5Mhz. I saw the board he had at the Alabama Broadcasters Association convention and it looked professionally made and the price wasn't bad.

For $850.00 I think I'll wait for DT's (hopefully lower cost) module.


COMMENGard

I think the price I heard was more like $350. I could be wrong..

Re: Crystal alternative

Posted: Fri Sep 14, 2018 12:52 pm
by Deep Thought
REW wrote:
Thu Sep 13, 2018 3:58 pm
COMMENG wrote:
Wed Sep 12, 2018 2:05 pm
REW wrote:
Tue Sep 11, 2018 1:18 pm
Micheal Paton from Baton Rouge, La. had a device for some of the Harris AM transmitters. I think he said it could be set via dip switch to output a frequency of .5 to 5Mhz. I saw the board he had at the Alabama Broadcasters Association convention and it looked professionally made and the price wasn't bad.

For $850.00 I think I'll wait for DT's (hopefully lower cost) module.

COMMENGard

I think the price I heard was more like $350. I could be wrong..
His $850 module is a drop-in replacement for the Harris SX series oscillator board. It is crystal-controlled.

Re: Crystal alternative

Posted: Fri Sep 14, 2018 4:30 pm
by kcbooboo
Regarding the ProgRock: "That's the one I'm using with some outboard interface electronics. It can be GPS-disciplined and once the parameters are stored in NVRAM it is very stable."

From what I understand, the GPS input is used to set an internal crystal correction factor, but it doesn't seem to be continuously updating, i.e. if the temperature changes, so does the oscillator's frequency. You have to cycle power to get the correction factor read by the cpu. It's not really a true GPSDO, such as the old HP Z3801A unit.

I built one and purchased the TCXO for it. Once I fixed the correction factor, it was within a fraction of a Hertz at 10 MHz (the default output frequency) and it held that quite nicely. Enclosing and heating the entire device with a good oven controller would make it much more stable, in my opinion, even using the raw 27 MHz inexpensive crystal.

In my planned application (replacing crystals in a 29 MHz simplex base station), I will need to turn off the TX output when it's not transmitting, so the receiver doesn't end up hearing the ProgRock's harmonic. I'm doing this by using the PTT line to change frequency banks, where each bank only has one output programmed.

Bob M.