[time-nuts] ACAM GP22 Chip

Hal Murray hmurray at megapathdsl.net
Tue Nov 24 14:44:04 EST 2015

th.allgeier at gmail.com said:
> I should say from the start that I am new to time and frequency measurements
> and not even an electronics engineer – but then I have been exposed to
> high-precision electronics for the last 25 years hence have picked up some
> dangerous degree of half-knowledge. 

Do you have a copy of Art of Electronics by Horowitz and Hill?

> In order to evaluate the chip I was planning to replicate John A’s
> experiment with the coaxial delay line from the HP5370b – but as my interest
> is in “measuring range 2” of the GP22 I need a delay of 500 ns or more
> (actually 1 µs sounds a better start). This is the equivalent of a 200 m
> length of cable. I fear trouble with this: Am I not getting unwanted
> inductivities if I use a coil of that size? 

The trick is that your coil has 2 wires.  It's a transmission line.

Here is the handwaving explanation: The current on the return path is going 
in the other direction and cancels out the inductance.

Twisted pair will work almost as well as coax, maybe better than cheap coax.

AoE has an appendix on transmission lines.  You can find lots of info on the 
web.  You need to terminate it.  You will want a scope to check the 

These are my opinions.  I hate spam.

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