Any easy/cheap way to calibrate a frequency counter?

Discussion in 'Radio Circuits, Repair & Performance' started by AE5KA, Jun 8, 2011.

Thread Status:
Not open for further replies.
  1. AE5KA

    AE5KA XML Subscriber

    I have a Leader 823S purchased well used from a service shop going out of business. I would like to calibrate it to its 1 ppm spec, and figure I'll probably have to spend the bucks to have a calibration company do it, but before I do I figured I could ask here to see if anyone has any tricks that would let me do this myself. And no, I don't have a Rubidium or Cesium clock.....

    Thanks,
    Chip
     
  2. KL7AJ

    KL7AJ Ham Member

    Do you have a dual trace oscilloscope and a WWV receiver? Does the counter have a time base output you can sample?


    Eric
     
  3. AE5KA

    AE5KA XML Subscriber

    I do have a Fluke Scopemeter 123 which has dual trace capability, and of course I have my ham transceiver. The 823S does have an output for its 10 mHz timebase. I think i see where you are going Eric, but the details elude me!
     
  4. AE5KA

    AE5KA XML Subscriber

    OK, this is what I did. I tuned the transceiver to WWV10 and was able to zero beat the 10mHz timebase signal against it, to less than a 1 Hz beat.

    Thanks for leading me in the right direction, Eric.

    Chip
     
  5. KL7AJ

    KL7AJ Ham Member

    I knew you'd figure it out. :) Now what you want to do, however, is recheck this at different times of day, because WWV will have some doppler shift on it. There's a much more sophisticated method that uses the WWV Audio tones, which compensates for doppler, but you need to build some sort of frequency divider for your 10 mhz output signal. Then you can compare the audio frequencies with a dual trace scope. Quite a bit more accurate, but probably overkill for what you need. :)

    Eric
     
  6. NM7G

    NM7G Ham Member

    I read this years ago, so the credit isn't mine. You can do a passable job w/o a scope, but with your ears. To make it work, the WWV signal must be quite strong (S9 or more), with little or no QSB. The objective is to get WWV and the counter time base sigs nearly the same amplitude, which in most case means attenuate the time base sig. by decoupling (spacing) or a pad Use AM mode on the station receiver/transceiver dialed to 10.000MHz, and tweak for a audible swooshing sound that happens when sigs are close to ZB. Headphones with good low-freq response will help. The swooshing gets slower and slower as you approach ZB. I did it three times throughout the day, as room temperature was coolest, average, and warmest (no A/C in shack), and found a mean. Equipment must run constantly until you're done. I think of this as pseudo-calibrated, but it's not difficult and it's free. 73, Gary
     
  7. KD8DEY

    KD8DEY Subscriber

    F=1/T :) ........
     
  8. AE5KA

    AE5KA XML Subscriber

    Hi Gary. That is exactly what I did, worked fine for my needs. I'll check it periodically to see how much drift or variation there might be.
    Chip
     
  9. K9STH

    K9STH Ham Member

    Another way is to watch the "S" meter on your receiver (in AM position, no BFO). As the signal from you counter's frequency standard gets close to the WWV frequency the "S" meter will start to flutter, slowing down the closer to the frequency that you get. When the meter moves from side to side at a slow rate, your actual frequency is the "flutter" rate per second. You can get the frequency where the "S" meter needle takes more than a second to move side by side. At that point you are within 1 Hz or less.

    This has to be done during the "silent" period. That is when no audio tone is present.

    Glen, K9STH
     
  10. NM7G

    NM7G Ham Member

    Glen,

    It's ironic, but just yesterday I needed my counter, then realized it had been idle for years, so powered it up to cook 24-hours. Today I did the scopeless zero beat procedure. You're right on about the S-meter. I spent most of the time trying to get a good balance between strength of the two sigs, using coax pads and moving my leaky chunk of wire from the time base spigot. WWV was S9 to S9+40, and I started watching the needle oscillate, and tweaked through and past ZB a few times to get the feel of the trimmer. At first the TS-930S was in Fast AGC, and turning AGC off helped. That might differ under other circumstances, but anyway, it went smoothly. The gear will be left on for a few hours, then I'll listen for the time base 2nd harmonic on 20 MHz. Just curious to see how close it'll be.

    Gary
     
  11. K9STH

    K9STH Ham Member

    Be careful turning off the AGC/AVC. Especially in the older receivers, the "S" meter won't function with the AGC/AVC turned "off".

    Glen, K9STH
     
Thread Status:
Not open for further replies.

Share This Page

ad: Mircules-1