[Elecraft] Elecraft Receiver

[Larry Phipps]

As I think more about it Geoff, I would need a pair of mixers in order 
to get the tuning right-side up again. A first conversion to, say 45 
MHz... and a second back to 28 MHz.  Injection would  be from a xtal osc 
for the first conversion and a VCO running in the 46-73 MHz range. High 
side injection on both would get the tuning back to right-side up. With 
two mixers, a strong mixer amp would be required between stages. I have 
a couple designs I have used with good success that are easy to 
implement there.

I can see this will take some thought to get the right set of compromises.

Larry N8LP


Geoffrey Mackenzie-Kennedy wrote:

>Hi Larry,
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>Defender of the Multiple Conversion Faith charging in !
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>>In the meantime, here's a concept I have been toying with building. The
>>R-388, like most Collins gear, uses front-end converters to shift a
>>whole band segment so that the rest of the receiver becomes a tuneable
>>IF. This brings back some of the problems associated with multiple
>>conversion receivers that the K2 beats the pants off of...
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>Glad that you said "associated" and not "occur"! The high IF receiver runs
>circles around the low IF receiver in spurious response / internal birdie
>performance IF the IFs are chosen properly and IF High Side mixing is used,
>all assuming that the right devices / circuits are used. The choice of IF
>and High Side mixing and devices /circuits applies to low IF receivers, but
>in their case there is a much smaller choice of IFs, even just for HF ham
>band coverage,and they must have good front end filters and internal
>shielding if one wants a "clean" receiver. I would suggest that the problem
>with "commerecial" High IF double conversion receivers for Amateur use,
>which has created the myth, has three parts 1) The technology used is not up
>to date in this fast moving field - it cannot be. 2) The production roofing
>filters are wide as barn doors, and the "retrofits" are not much better if
>you look down their skirts and their distortion contribution, who knows 3)
>Usually the choice of IFs appears to be driven rather than chosen.
>
>The main ham band only receiver here, homegrown, is double conversion first
>to low VHF where the roofing filter bandwidth can be selected - 1.5 kHz
>narrow.It is a "strong" receiver without any internal spurii above noise
>floor. Took much number crunching, but that occupied waiting time at
>airports.
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>I think that tuneable IFs are attractive for general purpose use if really
>good intermod performance is not sought , although it can be if one stays
>away from diode ring mixers and uses modernish "strong" mixers and
>amplifiers. Also opens the option for low noise crystal oscillators for the
>first LO in those bands where one needs low phase noise from the LO. Collins
>also had an an eye on frequency readout, and further opted for the low
>values of  IF / Signal Freq ratios, perhaps for VFO stability reasons, but
>because of the strong spurious responses on the high side, 2Fo - 2Fa = IF
>etc (where LO was high side), they needed good front end filters. So it
>might be worthwhile looking at say 24 or 28MHz as an IF. But beware of the N
>times signal frequency = IF monkeys, and friends.
>
>Good luck with whatever you do.
>
>73,
>
>Geoff
>GM4ESD
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