John,
at the IF output of a mixer harmonics and other mixing products appear up to very high frequencies.
According to an aural conversatio I had with an application engineer of Watkin Johnson the IF port should be terminated non reactive up to mixing products of 5 times the RF input and LO!
Neither a JFET amp nor a quadrature hybrid can provide this!
Even a "good" designed diplexer (bridged T-type) will have problems in the return loss at hgh frequencies due to its parasictics (self capacitance of the coil, self inductance of the caps).
Henning Weddig
DK5LV
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jwharding3@yahoo.com?subject=Re%3A%20Mixer%20Termination%20w%2FBalanced%20Amp>
| 7807
| 2012-09-22 12:29:03
| William Carver
| Re: AW: [emrfd] Mixer Termination w/Balanced Amp
|
> Even a "good" designed diplexer (bridged T-type) will have problems in
> the return loss at hgh frequencies due to its parasictics (self
> capacitance of the coil, self inductance of the caps).
> Henning Weddig
> DK5LV
And if that diplexer (bridged T-type) has a Q > 1, the series and shunt coils and capacitors have different values so the distributed capacitance of coils and self inductance of capacitors further degrades the bandwidth. W7AAZ |