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Re: Norcal 40a (testing 4.9MHz xtals)

 

It's good that you've found the problem. The issue with the counter affecting the source reminded me of what I saw in a counter I got from eBay. From my notes:

"Hey, I noticed this after connecting it to my 10.000000 TXCO from HamCom 6/19/15:? The output of my oscillator dropped from 10 dBm to 9 dBm, so the counter is loading it slightly.? Also, I turned on the scope and the waveform was somewhat distorted.? When I unhooked the counter, power returned to 10 dBm and the sine wave was clean.? To monitor without disturbing, an isolation circuit might be needed."

Also, from the technical information in the eBay ad:

"2 Measurement channels (channels are low impedance)"

So some kind of buffer on the input, presenting a high impedance to the tested circuit might be a good?idea.

73-

Nick, WA5BDU


On Tue, Nov 26, 2019 at 11:50 PM Ramakrishnan Muthukrishnan <ram@...> wrote:

On Tue, Nov 12, 2019, at 5:04 AM, Nick Kennedy wrote:
I've sometimes seen counters display harmonics. It could be a matter of overloading the counter. Try attenuating the signal to the counter a bit, possibly just be using a very small coupling capacitor.

Turned out that the berg connector that the counter vendor supplied had a faulty connector. A friend of mine had the same counter and with that counter the oscillator worked just fine.

Another observation with the scope is that when the counter is connected, the output waveform as shown in the oscilloscope is severely distorted. Perhaps the counter does have a low input impedance?

In any case, I can start the process of measuring the motion parameters of the crystals now for the Norcal 40a build.

73
Ram VU3RDD
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