[time-nuts] Why a 10MHz sinewave output?

Attila Kinali attila at kinali.ch
Tue Feb 7 21:03:27 UTC 2012


On Tue, 7 Feb 2012 21:59:18 +0100
Attila Kinali <attila at kinali.ch> wrote:

> > Related question:   Assuming I'm using 10MHz sine wave.   What's the
> > best physical cable to use?  Is there any good reason to use 50 ohm
> > cable?   What about 75 ohm?   I looked at a schematic of my counter
> > and it looks like the 10MHz signal hits some high impedance chip
> > inside.    RG6 seems like the way to go.   It's double shieled and
> > lots of cable TV parts could be used.
> 
> There is no particular advantage in one or the other, at least not
> for most applications. It's tradition that measurement and (most) RF
> gear uses 50R, while TV and radio uses 75R. (there was once a reason
> for this, but i don't know it).

Addendum: Your counter input is mostlikely 50R. Even if it just enters
a chip, as the chip itself should be matched to 50R. The input impedance
should be noted in the manual of the counter.

			Attila Kinali
-- 
Why does it take years to find the answers to
the questions one should have asked long ago?



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