HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: Ed H on August 25, 2020, 2358 UTC
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Hi Folks,
I am sure a few of you have seen the inexpensive frequency counters available on-line. I bought a couple out of curiosity, featuring an 8 digit LED display. They are quite useful, e.g. for adding to an old signal generator, but beware using them for more precise work.
A case in point - I acquired a Yaesu FRG8800 a couple of years ago, and decided it could benefit from a tune-up. I used one of the counter modules in the course of this, and alignment generally seemed to go OK. Except there was a constant offset either USB and LSB modes, around 300 Hz. That seemed odd, but since the radio was in spec according to book values, and the small error could be corrected with the "Fine" tuning control, I didn't think much of it, and put it down to drift during warm up etc. Recently, I had another reason to bring the set back to the bench, and since I now have a better frequency counter, decided to look at alignment again. Lo and behold, the local oscillator settings for both USB and LSB final detection were incorrect by practically the same amount, and consistent with the error in tuning the radio. Using the new counter, and following the alignment procedure again has put the radio spot on frequency. Lesson learned!
Cheers
Ed
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I don’t know which frequency counter module you have, but if it is similar to this one, it does have an adjustment for the counter timebase.
https://www.mpja.com/Frequency-Meter-6Digit-100KHz-65Mhz-Blue/productinfo/35059+TE/
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If not the same, it looks very close. Thanks for the tip. I'll have to scare up some instructions, but I'll be interested to see if accuracy can be improved.
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For accuracy and a decent price you'd want one that has a TXCO and the ability to have a correction programmed in, so that even when the reference clock is off a bit, it can be corrected so you'll have an accurate reading.
We had them in the labs, but I don't know what the current, inexpensive version of this product would be, but it should be trivial to implement in any counter today.
K-Bear
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Thanks again for all replies.
For bench duties, I recently sourced a decent used counter from a popular auction site. It has a temperature stabilised reference, and gives trustworthy results. Listening to the 10 MHz reference against WWVB on a receiver, it is rock solid and within a Hertz or so after warm-up.
Cheers
Ed