[time-nuts] Data collection cycle -- multiple sources toonecounter?

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Jun 19 13:41:44 EDT 2005


In message <42B5AC9A.20305 at onetel.net>, David Kirkby writes:

>The attenuator will reduce a 1W source to 250mW (6dB attenuation). 
>Assuming the load on the output of the attenuator is open or short (so 
>100% reflection), the power will be reduced by another factor of 4 (to 
>62.5mW) before it reaches the source. So only 6.25% is reflected back to 
>the source. That's a VSWR of less than 1.7.

Be aware that there is a big difference in impact on square and sine
signals.

Even a minor change in circumstances will push the zero-crossing of a
sine wave signal one way or the other.  This is because (compared to
a square-wave) the slope at the zero-crossing is very low in terms
of V/s.

Also, if measuring squarewave signals, be sure to choose your trigger
point wisely.  Many digital drivers control for the V(il)/V(ih) voltages
and neither is likely to be V(max)/2.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.




More information about the time-nuts mailing list