[HBR] 6BE6 Mixer Question

[Walt Hutchens]

Tim said:
> Loud signals should be loud and weak signals should be quiet.

That's a matter of having the right amount of AGC action.  While
normal AGC cannot actually hold the volume flat, a set with too many
controlled stages can hold it flatter than you'd like, so that the
'ear test' (as above) doesn't work very well.  I have a USN SRR-13
that controls maybe 5 stages?  Definitely too much.

It is also possible to use feed-forward AGC: You control (say) three
previous stages (to the detector) and one stage following.  This will
get you an absolutely flat or maybe even a falling AGC characteristic.
(Loud signals could be lower volume than weak ones.)  The only
receiver I know of that did this was also military and I cannot
remember the number right now.

Rather disconcerting: I'm like Tim -- very strong signals should be
louder.

Mixers generally shouldn't be controlled.  You can decouple the
oscillator so detuning doesn't occur but you've still got the problem
of reduced crossmodulation performance.  In a home brew receiver
without an RF stage, however, an AGC controlled mixer can work okay
since the signals at the mixer will be much smaller than with a
preceding stage.

Walt Hutchens
KJ4KV