[time-nuts] HP10514B Mixer Terminations

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Sep 10 06:35:16 UTC 2012


Jim Lux wrote:
> On 9/9/12 9:37 PM, lists at lazygranch.com wrote:
>> What am I missing here? Vce = Vbe, so the diode connected transistor 
>> isn't saturated.
>>
>
>
> I think it's where the diode is fully conducting, and into the linear 
> part of the V/I curve, not in the square law part any more.
>
> In normal use the LO port is driven hard enough that the mixer is 
> (hopefully) acting as a switch (and RF port is <-10dB relative to the LO)
>
>
> _______________________________________________
Not quite, its when the LO input is large enough to switch the diodes 
and the RF level is comparable to the LO level..
If the IF output level (for a fixed LO level) is plotted against the RF 
input level, the curve exhibits a knee and the IF output level saturates 
at a fixed level when the Rf input level is sufficiently large.
At low signal levels the IF output signal level is a proportional to the 
RF input level at high Rf input levels the IF output level approaches a 
limiting value.

Bruce



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