Arv,
I get the same carrier level in the spectrum analyzer with a tone or
without a tone, just the two-tone generator output impedance as a
termination.
When you say to terminate the mike input what impedance are you
thinking of? I've attached a png of the output circuit of the two-tone.
I use the line output which basically offers a 33K impedance to the mic
input.
I don't think it is the diodes themselves. If one or both of them were
bad I wouldn't expect even 25db of suppression.
I've never been a big fan of this kind of balanced modulator. There
isn't much you can do to maximize carrier balance. I thought perhaps
it might be unequal inter-winding capacitance in T7 so I did the
best I could to equally space all the windings around the toroid and
the wire length to the circuit board but it made no difference at all.
I haven't tried yet but I've thought about lifting C63 to isolate the
mic pre-amp to see if that makes the carrier suppression better. I've
got everything torn down now to move the circuit board closer to the
back so I can use the box as a heat sink. When I get it all back
together I will try liftin C63 to see what happens.
tim ab0wr
On Sat, 28 Apr 2018 17:10:53 -0600
"Arv Evans" <arvid.evans@...> wrote:
Tim
Interesting. How much carrier suppression do you get without tone
insertion?
Just terminate the mike input and balance the modulator without any
modulation
being inserted. If that dip is too shallow then it could point to the
modulator diodes
themselves.
Arv
_._
