Under the same conditions, none of my other radios don't have this problem.
After substituting the 1st mixer for the MCL unit, the IMD products are now
gone. Another problem is the approach the designers took with this radio.
The gain distribution is not set up properly. Instead of having the RF
amplifier ahead of the 1st mixer, they should have placed the 2N5109 after
this mixer.
I still need to do more work with the impedance matching network that
follows the mixer. I have installed a diplexer, but I really need to measure
the 30MHz crystal filter impedance so I can properly calculate the values
required for a matching network.
A series L, shunt C seems to work pretty well in this application. With the
initial calculations for a 3k impedance, I have reduced the dip in the
response down to 2dB, but I know that I should be able to decrease the
passband ripple to less than 1dB.

Pete

"Telamon" wrote in message
...
In article
,
"Pete KE9OA" wrote:

Has anybody ever changed the 1st mixer diodes to hot-carrier types. I
have
one of these in my possession and the IMD is terrible. They've got to be
using ordinary switching diodes for the performance to be this bad. I
notice
that they are using a 2N5109 post mixer amplifier, so I don't understand
why
they would skimp on the mixer diodes.

I'm have no experience with radio RF mixer circuits but maybe you are
just over driving it?

--
Telamon
Ventura, California