12/23/2018 at 03:16 •
DISCLAIMER: I have no stable enough frequency source so the accuracy and stability are not tested here.
2 years ago, I have bought 3 of these crystal oscillators from eBay :
(picture courtesy of the seller bg2014-manue, thanks for the cross-linking !)
In theory, if the frequency drifts by less than 1Hz at 10MHz, that's in the ballpark of 0.1ppm (or 100ppb ?) but without a proper equipment, I can't validate the frequency accuracy and stability. I'm trying to solve this for a long time, if you remember my burned Rb oscillator :-D
I think these Philips modules are a good compromise for price/performance/ease of use. Only recently did I test them so I went google-surfing. I could only find partial information but cross-checking different sources gave me some confidence about the pinout. For example the document "Frequentie standaard" by PA0WSO (in Dutch) gives a good example of how to use the module but the pinout is not defined.
The right hand half shows the temperature compensation, using a resistive element. A TEC could be used instead if ambient temperature rises above 25°C. The lower left quadrant shows the varicap control for tuning/"pulling" the oscillator.
Another useful document "A 10 MHz Timebase Clock for Frequency Counters - complete with a PLL for DCF77" shows the pinout but it might not apply to this variant : apparently there are several permutations but as long as you get the right VCC, GND and voltage, you can probe the pins with an oscilloscope.
If you get the pinout right, these 2 application documents help with the design of the pulling and amplification of the output.
A forum page shows the following pinout :
The assignation is correct BUT my specific model is not "pulled" by a resistor, but with added capacitance.
Luckily, Philips has used these modules in their own lab devices (PM6670 and PM6672) and they appear in the service manual :-) The above forum page provides the .djv file, along with other measurements. The TCXO is mounted on optional module PM9678B
WHY would the use a poor BF245 to handle 60mA ??? And here, the adjustment cap is on another pin...
The rest of the service manual shows the amplification but there is no heat management.
(if you find more references, I'll be happy to include them. I remember seeing a catalog/datasheet that shows the various pinouts and options but not it evades me)
I measured a few things that I write down here. But first here is my pinout diagram for this specific model :
Don't connect the other pins.
- 0V : just the ground.
- Vcc : I don't know why there is a resistor. Maybe there is an internal shunt regulator but since the current increases with voltage, I doubt... The doc recommends 470 Ohms and 12V, but the 60mA drops the input to about 7.4V. I suppose these values will change with temperature, input ripple, and whatnot... Generous decoupling is recommended (ceramic+electrolytic ?).
- The output: the 'scope shows it's 0V-centered, meaning there is an internal capacitive coupling. I also noticed the frequency slightly varying depending on output capacitance or impedance, I'm not sure... The amplitude is weak, buffer it with a high impedance amplifier (JFET input ?).
- There is another pin for adjustment, also called I.C. on some models. In this specific model, this is a capacitive pulling. I observe a lower voltage version of the output, don't touch this pin or you'll detune it... NOTE: FREQUENCY ADJUSTMENT IS NOT TESTED YET.
Here is how I quickly tested the CTXO :
Yes it's ugly but enough to check that it works :-)
When displayed on the 2467:
Here it's using a 10x setting for the probe so we might infer about 400 or 500mVpp. The amplitude and waveform vary significantly when using the 1x probe so impendance matters !
Looking with the DSO : amplitude is...Read more »
12/21/2018 at 05:35 •
@Drew Fustini posted this :
It deserves a CAD version !!! Who wants to try ?
11/21/2018 at 04:30 •
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