> And this is why the cumulative contribution of noise
> by a multitude of mixer stages is such a thorn, not
> only do you have the original noise you are
> incrementally adding more in each mixer stage.
While I am not a "fan" of needless mixers, I think we might be
encouraging mixerism.
For example, all of the annoying hiss in FT1000's comes from a
single IF amplifier stage just after the last narrow 455kHz filter.
Very little (certainly nothing noticeable) comes from the mixers.
Most receivers I've looked at with annoying hiss have been victims
of poor gain distribution or noisy stages after the narrow filtering,
where bandwidth is so wide everything (including both sidebands)
gets through.
Stages after the last narrow filter are critical. From that point to
your ear the system is a double-sideband wide-bandwidth system.
We not only hear noise power from the desired sideband with
virtually no selectivity (remember noise power is reduced in direct
proportion to bandwidth), we also get noise from the opposite
sideband!!!
73, Tom W8JI
W8JI@contesting.com
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