Re: 80 meter superhet
You need impedance mathing at both ends of the xtal filter.
Do you have any idea of the filter impedance ?
What kind of filter is it ? Homebuilt ?
A diode mixer is a low impedance device and often xtal filters need about 500ohm drive and load impedance. So you need a toroid that transforms 50 to 500ohms. This means a turns ratio of 3.33.
Note that the inductance of the toroid must be so high that the inductive reactance is 4-5 times the needed impedance, i.e. for 500ohms and 11MHz around 30uH.
It is also possible to use an LC-filter to match from 50ohms to the filter impedance.
Also note that a diode mixer needs quite a bit if drive to overcome the threshhold voltage of a diode of around 0.6V. Too low drive power gives a lot of loss in the mixer.
Regards,
Urban
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