V
VK2RK
Guest
As GPS referenced oscillators along with cheap Oven Controlled Oscillators are becoming available at low cost, one can now provide a signal reference to your old counter with a simple modification if no external port exists.
A typical circuit used in instrumentation is the colpitts crystal controlled oscillator (https://www.electronics-tutorials.ws/oscillator/colpitts.html)
This makes the addition of an external reference a very easy thing to do.
Other types of oscillator do exist but the modification should also work on them, note that the injection point in all cases has to be done at the oscillator adjusting point (Trim Cap)
10MHz Counter time base diagram
The addition of an external signal via a coupling capacitor will dominate and force the oscillator to output the reference frequency
a switch can be added but I find this not necessary.
If its required to have accuracy with just the internal oscillator the extra capacitance of the added components need to be compensated for.
If its found that the range of the trimmer is not enough to bring the internal oscillator back to wanted frequency then the coupling capacitor value needs to be reduced.
Typical value for the coupling capacitor ranges from 2 pF to 5 pF, if you get sufficient injection from your reference then smallest is better.
Parts required
BNC socket mount female
Capacitor
Lenght of miniture coax (As short as possible)
Counter with the above modification
This counter had no external reference port, the above modification made this instrument very accurate
A typical circuit used in instrumentation is the colpitts crystal controlled oscillator (https://www.electronics-tutorials.ws/oscillator/colpitts.html)
This makes the addition of an external reference a very easy thing to do.
Other types of oscillator do exist but the modification should also work on them, note that the injection point in all cases has to be done at the oscillator adjusting point (Trim Cap)
10MHz Counter time base diagram
The addition of an external signal via a coupling capacitor will dominate and force the oscillator to output the reference frequency
a switch can be added but I find this not necessary.
If its required to have accuracy with just the internal oscillator the extra capacitance of the added components need to be compensated for.
If its found that the range of the trimmer is not enough to bring the internal oscillator back to wanted frequency then the coupling capacitor value needs to be reduced.
Typical value for the coupling capacitor ranges from 2 pF to 5 pF, if you get sufficient injection from your reference then smallest is better.
Parts required
BNC socket mount female
Capacitor
Lenght of miniture coax (As short as possible)
Counter with the above modification
This counter had no external reference port, the above modification made this instrument very accurate