[time-nuts] Distribution amp - Use a video amp unit ?

Charles P. Steinmetz charles_steinmetz at lavabit.com
Mon Mar 26 18:01:34 UTC 2012


Randy wrote:

>if one is distributing 10 Mhz, does it really 
>matter what the circuit does at 300 and 900 Mhz??

That depends on what it is feeding and what noise 
and other signals are getting to the DA 
input.  Some synthesized 10 MHz sources produce energy well above 10 MHz.

I consider nonmonotonic behavior to be a design 
flaw in general (except where it is specifically 
desired or you are up against the bleeding edge 
of technology and it can't be avoided), so I 
eliminate it at every opportunity as long as the 
fix doesn't cause worse problems.  In this case, 
the nonmonotonicity is cured by replacing an 8¢ 
transistor with a 16¢ transistor, and some other 
small benefits are realized at the same time, so 
I say it's 8¢ well spent.  Nearly a whole dollar 
extra for a 12-output DA.  The noise bump is 
cured by restricting the 3 dB bandwidth to ~80 
MHz, which does not affect the 10 MHz but may 
help the receiving instrument if it is sensitive 
to VHF noise (although the magnitude of the bump is not large).

I consider these good prophylactic design 
measures.  Practicing them keeps you out of 
trouble that you might not even know was 
threatening, whether or not it makes a practical 
difference WRT a particular design.

Best regards,

Charles










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