[time-nuts] mixers for frequency measurement

Bob Camp lists at rtty.us
Thu Jan 19 13:04:08 EST 2012


Hi

Complicating the matter - the time it takes for the junction to go from full
on to full off also contributes to the noise. An ideal mixer would switch
instantaneously.... It's always a tradeoff between various noise sources.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of ed breya
Sent: Thursday, January 19, 2012 12:36 PM
To: time-nuts at febo.com
Subject: [time-nuts] mixers for frequency measurement

Yes, they are Schottkys, just like the ones used in most mixers - but 
much bigger and slower. They would have to be properly impedance 
matched, and could be driven to higher power levels, with higher 
diode conductance, so (I think) much lower noise. Of course, 
amplifying up to higher power will add noise, so it's not "free" in 
that respect.

Ed

Stefan wrote:
1N5817 are schottky diodes. Wouldn't they saturate much earlier than 
a 2N2222A? If saturation is the right word with a schottky diode...

I wrote:
 > 5 or 10 MHz could be made even better. I wonder how a ring of matched
 > 1N5817s would work at saturated power levels - maybe +20 dBm or so.




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