[time-nuts] Sub Pico Second Phase logger

[Brooke Clarke]

Hi Bruce:

A general comments on mixers.

Since they are very nonlinear devices the output consists of signals at:
+/-m * RF +/-n * LO.
The output will change if the termination on any of the ports at any of those 
frequencies is changed.  How much it changes depends on how strong that signal 
is.  Some mixers reflect the image frequency to improve the conversion loss of 
the desired output.

For the mixers I was working with the LO needed to be strong enough to drive 
the diodes into saturation and the RF needed to be small enough to not effect 
the LO power.

More on that at:
http://www.prc68.com/I/Diodes.html

Have Fun,

Brooke Clarke
http://www.prc68.com

Bruce Griffiths wrote:
> Joe
> 
> I suspect that the phase detector characteristics stated in the NIST
> papers only apply when the mixer RF port is saturated.
> This is evident from the Kurtz application note:
> 
> http://www.wj.com/archive/documents/Tech_Notes_Archived/Mixers_phase_detectors.pdf
> 
>  which indicates (Figure 14 and Figure 15 plus surrounding text)  that
> for a high impedance (resistive) IF port termination the phase detection
> characteristic only approaches a triangular wave when the RF port is
> saturated (Figure 15) whereas for an unsaturated RF port (Figure 14) the
> phase detection characteristics still appears sinusoidal.
> The Kurtz application note also indicates that the IF port signal
> amplitude reaches a maximum when the IF port termination resistance
> increases (for the particular mixer) above 400 ohms.
> 
> There are no corresponding figures for the case of an IF port terminated
> in a capacitor.
> It would be interesting to check this.
> 
> Saturating the RF port also degrades the isolation etc, thus another
> interesting question is does capacitively terminating the IF port
> degrade these parameters when the RF port is unsaturated?
> This may well not be the case with 5MHz or 10MHz mixer input  frequencies.
> 
> 
> Bruce
> 
> 
> 
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