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Tim Shoppa · December 24th 06, 09:04 PM posted to rec.radio.amateur.homebrew

wrote:
But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

The DeMaw designs are very nice but with their band-wide converters
they also suffer from having selectivity downstream rather than at the
front. Preselection at the front helps with any of these.

The modern choice of a 45MHz or so first IF is really pretty nifty for
a general coverage receiver from the past couple of decades. Lack of
preselection can be largely cleared up by bolting something before the
front end, and indeed many of the receivers you see that cost as much
as a car have tracking preselectors.

But if you don't want to upconvert, as I see it you have two choices:

1. Don't even try bandswitching. Coil sets for each band. You end up
with the HBR-16, a very elegant and homebrewable receiver.

2. Do bandswitching but with elaborate tracking front end (and if
necessary a tracking IF, but with modern synthesizers you probably
wouldn't), probably with many switching sections to handle the required
octaves. You end up with a R-390A.

Tim.

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