Tio Pedro wrote:
I was thinking of using a toroid to provide the LO injection
to a balanced mixer, using a trifiliar wound transformer
driven by a cathode follower. Has anyone tried that scheme?
On the other hand, adding a cathode follower means that
stage could also be used as a phase inverter and the drive
taken from the cathode and plate, eliminating the need for
a broadband transformer. Anyone have experience with
either means?

Pete


No, I haven't tried that particular idea, but here are some thoughts:

Are you using the transformer to the grids or the cathodes? Are you
going go broadband or resonant? If broadband, are you going to be able
to generate sufficient voltage before you run into problems with excess
inductance? Have you considered loading the output (if you're going to
the grids) and just giving it excess drive?

I would expect (but I haven't tried it) that a phase inverter would have
all sorts of parasitic problems at RF, so you'd have trouble making sure
that your phase was really 180 degrees out and that your amplitudes
matched -- any mismatch of phase or amplitude will unbalance your mixer,
to the detriment of your carrier suppression. I would expect (but I
don't know) that a center-tapped transformer, either resonant or
broadband, would give you better balance.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html