On Wed, 7 Nov 2018, Paul wrote:

Most ( if not all,) H mode and switching mixers employing 4066 and FST
chips are designed for IF frequencies, typical , with a 9Mhz diplexer.

I want to experiment with simple dc rx, so , I want audio out from these
mixers, but, they terminate with an RF balun! How do I extract the audio
component, , snd connect an audio diplexer?

If there's a balun, it won't pass low frequencies.

Terminating mixers were for a while just an RF thing. It took a while for
the concept to be applied to direct conversion receivers, which I suspect
is one reason endless work was done on the mixers in such receivers, and
not much progress was made.

About 1983, Gary Breed had an article in QST about a phasing direct
conversion receiver, and I think that was the first time anyone described
a terminated mixer in a DC receiver. It was using diode ring mixers, and
using the one port that was DC coupled for the audio output.

Roy Llewellyn had a very tiny transceiver somewhere around that time (so
maybe it was first), including a DC receiver, I think a diode mixer, with
termination.

KK7B, I think it is, has really done a lot on the subject, a series of
receivers in QST, I think he uses diode mixers but he also terminates
them.

People have used CMOS switches as mixers, and no balun at the output. I'm
sure some have been terminated at audio.

You just need to look more, probagly the ARRL Handbook now has material (I
bought the 2018 edition, after 17 years of not buying one) but I've not
gogten to it, the construction projects are now mostly on the CDROM, which
is actually now a downloadable file. "Solid State Design for the Radio
Amateur" probably has a bit about terminating mixers, but for RF, and
probably diode mixers. The more recent ARRL book that is supposed to be
an "update", I forget the title, should have it, the book is old enough
that it went out of print, and then was brought back despite it being
"old".

You need to find CMOS switch mixers that are directly coupled to the next
stage, that will then allow you to get audio output out of them, and
terminate them properly at audio. I'm sure a proper search will turn up
results on the web, I just don't have any URLs handy.

Michael