[time-nuts] schematics of frequency counter

Bob Camp kb8tq at n1k.org
Wed Dec 24 15:32:32 EST 2014


Very interesting !! Thanks for sharing. 

As you can see from the Fluke schematics, the input amplifiers on counters can get quite complex. I would definitely recommend playing a bit with the input channels on your board. Here’s what I would do, there are many other approaches:

1) Set up a high speed CMOS biased gate limiter with an OCXO. Quick approach is two 10K ohm resistors for bias (one to B+ one to ground), AC couple the sine wave into the junction. Junction also goes to the gate input. 

2) Assume that the signal is good. (it may not be).

3) Compare the CMOS signal on one channel to your input amplifier on the other channel. 

4) Attenuate the signal to the input amplifier and see what happens.

Again, there are *lots* of different ways to do the same sort of thing. I would not go overboard doing this with complicated circuits. You simply want a way to figure out what the input circuits are doing.

Have Fun!


> On Dec 24, 2014, at 11:19 AM, Li Ang <lllaaa at gmail.com> wrote:
> http://www.qsl.net/bi7lnq/freqcnt_bi7lnq_v4.pdf  this is my current board.
> I'm not a hardware guy, feel free to correct my mistakes. :)
> http://assets.fluke.com/manuals/6690____smeng0000.pdf schematic of cnt90
> aka pm6690
> Happy holidays
> Li Ang
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