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how accurate you say it is ???

1iwilly

1iwilly

Sr. Member
Dec 7, 2008
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i pick up a cobra 2000 gtl that was in need of TLC so i put the clarifier back to stock my question is how accurate is the built-in frequency counter. when i realign the frequency with my bk meter the counter is off like 27.1850 the counter reads 27.1843
 

All frequency counters use a crystal to time the measurements it makes. And that crystal usually has a trimmer capacitor attached, so you can make up for the way components will drift with the passage of time.

That being said, ANY counter that hasn't been compared to a reference like WWV is bound to be at least a little bit wrong.

Tricky part is how much?

Making two counters read EXACTLY the same is easier if you can calibrate all of them to the same reference. Hard to do without one.

Some counters use a crystal that has a harmonic you can hear in a shortwave receiver at the same frequency as WWV. The trick is to 'borrow' some of the harmonic from inside the counter, and feed into the receiver's antenna input alongside the WWV signal coming down from the antenna. The counter harmonic will beat with WWV's carrier. Set the counter's trimmer cap to zero beat with WWV's carrier and you're good to go.

And if your counter uses a quirky crystal frequency like 6.5536 MHz or 5.188 or such this won't work. We have calibrated our Hewlett-Packard counters this way for years. They have a 1 MHz output from the counter's crystal reference that works with any of WWV's on-air frequencies. Really handy.

73
 
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When I was in broadcasting we had to maintain our AM transmitter frequency to within 10 Hertz of assigned carrier frequency. We had a string of 1 Kw stations stretched out over 110 miles but was able to check them each day from the office. We had a Hammurlund HQ-140 receiver and a long wire antenna. Connected to the receiver also was a variable oscillator with fine tuning and a frequency counter was connected to it's output and lightly coupled to the receiver. We would tune in out station and then tune the oscillator for zero-beat against the carrier and read the frequency on the counter. The Dept. of Communications as it was called way back then was impressed with the accuracy we were able to obtain remotely using this method. We could actually get to within +/- 1 Hz or better. The signal strength would bounce up and down as the two signals (carrier and oscillator) would beat together in the receiver and when it peaked and stood still a reading was taken. Periodically we would calibrate the counter's internal 10 MHz clock oscillator using the same technique but would beat it against WWV. It worked very well and met calibration standards.
 
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