Frequency counter questions - calibration?

Discussion in 'General Technical Questions and Answers' started by KV4JW, Nov 8, 2018.

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  1. KV4JW

    KV4JW Ham Member QRZ Page

    Picked up a "CB radio" type frequency counter ($5 yard sale score!) with an RCA jack on the back and I'd like to use it for some light testing, etc.

    I'm doubting the accuracy of the frequency counter though. I mean, it's in excellent condition, but it's an unknown piece of equipment.. There IS a calibration adjustment inside the FC, but I'm unsure how I could actually generate a test frequency in which to calibrate the FC against.

    I DO have a BK Precision 2005B analog signal generator, the only caveat is, it's analog and unless I have a FC reading it, I have no sure 100% idea of where it's transmitting. I see there's a port to plug in a crystal on the front. I have some junk CB's in the parts bin that I could perhaps rob a crystal out of, would that work, or is that not what that's for?

    I also have an Icom 718 HF rig, would I perhaps be able to transmit a very low power into a dummy load on say, 7.000.00 or 14.000.00 or something and use this to calibrate the FC? I understand I'm not going to obtain a precise calibration other than sending this thing off to a lab or something, or finding someone with a calibrated and highly accurate RF source.. At the same time, I wouldn't expect 100% accuracy from a FC of this design/purpose anyway.
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Can you receive any of the WWV transmissions on your Icom 718?

    If so:
    - Let your rig, generator and counter warm up a while
    - Tune in and then zero beat WWV (e.g. 10.000 MHz), your rig's display may or may not be accurate so focus on the point of zero beat of WWV's carrier whether or not your rig reads exactly 10.000 MHz
    - Loosely couple your signal generator to your rig (or directly couple the gen to the antenna port with sufficient attenuation or a low enough generator output)
    - Tune your generator frequency for a zero beat without retuning the receiver
    - Test and or adjust your frequency counter to match the frequency (e.g. 10.000 MHz)

    If your rig doesn't have WWV support then you can use other known transmissions (the maritime net on 14.300 or one of the 40m shortwave stations can get you pretty close but a standard like WWV is much better).
     
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  3. KV6O

    KV6O Ham Member QRZ Page

    You're on the right track in thinking. To calibrate your counter, you need a reference. You can buy a 10Mhz reference that is generally more than good enough for ham use for not much. Barring that, you can use a known good radio to act as a reference, or to transfer the "better" reference. I'd see how your 718 is performing against WWV, and calibrate it if possible. Then, you can use it as you mention (into a dummy load) to provide the reference that you calibrate your counter to.

    There are several pitfalls in this method, but it probably good enough to get you within +/- 25Hz or so, better if your careful. A cheap frequency counter might not even have that resolution, or stability to begin with, so probably "good enough".
     
    KV4JW likes this.
  4. KV4JW

    KV4JW Ham Member QRZ Page

    I'll try this this evening. I've never tried to receive WWV, but it's certainly worth a shot, and free.

    If the WWV method doesn't yield decent results, I'll do some digging around for a 10mHz reference crystal. :)
     
  5. K9STH

    K9STH Ham Member Volunteer Moderator QRZ Page

    In most counters, there is a crystal controlled standard. Most of those operate on like 1.0000 MHz, 5.000 MHz, or 10.000 MHz. With those, if you get the counter near a receiver capable of receiving WWV, you will be able to hear a beat note between the counter and the received signal. You need to use AM, not SSB, to do this.

    Adjust the calibration on the counter until the beat note disappears. Watch the "S" meter and it will start to vibrate, rapidly at first and then slower and slower. When the needle is going from side to side slower than 1 vibration per second, you are within 1 Hz of being on the same frequency as WWV.

    There were a few inexpensive counters that used a 3.579 kHz TV receiver crystal for the standard. But, those, generally, do not have any means for calibration.

    This direct radiation method is how most field calibration is done.

    Glen, K9STH
     
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  6. K8JD

    K8JD Ham Member QRZ Page

    WWV is the standard that anyone can check against. Most newer ham rigs can tune to WWV, 2.5 and 5 MHz at night and in daylight, 10, 15 and some days 20 and 25 MHz can be heard. Zero beat to verify a local device you want to calibrate. If a ;synthesized rig can checked on those frequencies it will also be accurate anywhere.
     
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  7. G3YRO

    G3YRO Ham Member QRZ Page

    Much easier than trying to exactly zero beat WWV is to go on the Medium Wave (AM) band with your IC718 and tune in a broadcast station.

    Find one playing music, tune in on SSB, and it will be obvious if you're even 5Hz off frequency ! (the music harmonics will be all out of tune). You can even switch between LSB and USB to make sure you're exactly on frequency, as when it's right, there will be no change in pitch of the music.

    If the display isn't reading exactly 0.00, then you need to adjust your rig's reference oscillator - set the dial so it is exactly 0.00, then adjust the trimmer until the music sounds right.

    (I'm presuming your US Broadcast stations have to meet the same high accuracy of frequency as our British stations . . . and being on a low frequency, the percentage error will be small).

    Once you've accurately set yout rig, just radiate a carrier and use it to adjust the trimmer in your Frequency Counter (on as high a frequency as possible)

    Roger G3YRO
     
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  8. WA4ILH

    WA4ILH Subscriber QRZ Page

    Roger's remarks are right on. US Standard Broadcast stations must be within +/- 20 Hz of their assigned frequency. Most are much closer, within 10 Hz. The simplist solution, if you have an AM broadcast station nearby, take your counter near the tower (stay legal) and adjust the trimmer for the correct frequency.
    Tom WA4ILH
     
  9. G3YRO

    G3YRO Ham Member QRZ Page

    Yes but if he adjusts the master oscillator in his IC718 so it's on frequency against the Broadcast Station FIRST (which is well worth doing), then he can use THAT as a frequency source to adjust his Frequency Counter !

    Roger G3YRO
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    Why would you need to be messing with the master oscillator adjustment on the IC718 ?

    That would be learning the hard way. :eek:
     

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