[time-nuts] schematics of frequency counter

Li Ang lllaaa at gmail.com
Fri Dec 26 08:21:41 EST 2014


Hi
    Thanks for the suggestion. I will do some experiments with the front
end :)

2014-12-25 4:32 GMT+08:00 Bob Camp <kb8tq at n1k.org>:

> Hi
>
> 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!
>
> Bob
>
>
> > 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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