[Elecraft] Receivers.

[Geoffrey Mackenzie-Kennedy]

Morning Bill,

It never ceases to amaze me how receivers (and antennas) attract so much
comment. Is it because the majority of us are using receivers designed for
the amateur market as benchmarks, or is it something that results from
habit? I suspect that the "Money Men" get involved closely in the design

My $0.02 worth for ham band only coverage:

1) Dual vs Single conversion. Both can be a disaster if the IFs are not
chosen properly  With the IFs chosen properly, and the receivers built
properly, up-conversion to the first IF with the LO on the high side, there
are far far fewer spurious responses to be found in a dual conversion than
found with a single conversion receiver, and "weaker".  The RF preselector
in a "Dual" has something more to add to attenuation. 'Built properly' is
very important.

Narrow first IF filters are essential in double conversion for "strength"
reasons, selectable by reed relays not diodes. Here I use VHF 12 poles, 6,3
and 1.5kHz.

2) Effect on Noise Floor.  Assuming the use of strong mixers (+50dbm) and
strong low noise figure IF(s), the difference can be zero.

3) LO purity. Both require a low phase noise LO(s), free of spurs. Until a
cheap low phase noise PLL appears, I'll stick with premix systems running at
VHF. Much more work, but worthwhile.

4) DSP. I fully agree. I see little point in having a ho-hum filter at the
front end of the IF, letting a cocktail of signals romp down the IF to be
dealt with by a DSP module. Great will be the day when a DSP unit running at
VHF, with a high IP3in etc, and low noise figure becomes practical.

73,
Geoff.     GM4ESD