[Hallicrafters] How do they do it?

[Philip Atchley]

Hello all
I've been doing some very extensive SWLing with the SX-71 receiver.  In
fact, it is now my 'primary' listening rig.  One thing I have noticed about
this set is it's very good selectivity (we're talking AM reception here)
Even in the 'normal' selectivity position, I.E. Xtal filter off this thing
is selective enough to slice off some of the higher AM sidebands,
particularly on music.  Of course if you go to 'Xtal Broad or sharp' it is
even more selective.

But I wonder.  How do they get this degree of selectivity given the few
actual tuned circuits in the IF section?  Yes, the old Collins R-390 (not A)
receiver used only tuned LC circuits (and a Xtal filter for really sharp
selectivity) but had many more of them.  Is the Xtal filter somehow still in
the circuit even when it's in the 'normal' position?  True, I haven't
measured the response, but my "ear" tells me the selectivity is there.

73 de Phil  KO6BB
Loving home provided for wayward Boatanchor Receivers
k06bb at elite.net
Merced, Central California
37.18N  120.29W  CM97sh




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