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From: mjj@stda.jhuapl.edu (Marshall Jose)
Newsgroups: rec.ham-radio,rec.radio.shortwave,sci.electronics
Subject: LSB/USB mod to Sangean 803 / DX-440
Message-ID: <1990Dec7.144911.174@aplcen.apl.jhu.edu>
Date: 7 Dec 90 14:49:11 GMT
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Reply-To: @aplvax.jhuapl.edu:mjj@stda.jhuapl.edu (Marshall Jose)
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Organization: The Johns Hopkins University Applied Physics Laboratory
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I hope this isn't old news.  I recently picked up a DX-440-on-sale, as well
as a service manual for same, and soon set about trying to figure out
how to make it receive one sideband or the other.

After getting past a delusional fixation I had about needing additional
IF filters, I tried someone's advice:  use the narrow (4 kHz) filter,
and shift the BFO up or down 2 kHz as is needed to receive the proper
sideband.  It works!  And rather well, indeed.

Great, but to shift the BFO you will have to get inside the unit.  The
"BFO" control on the front of the DX-440 only shifts the 1st LO -- it
doesn't affect the BFO frequency at all.

The one to twiddle is VT103 on the A-1 assembly, which is a 100 pF trimmer
capacitor in the BFO xtal oscillator circuit.  Of course, doing this means
that you're stuck with one or the other sideband mode after you reassemble
the radio case.

I'll be puttering around in the next week or two with ways to make the
mode switchable, preferably with a minumum of holes cut in the case.
I'll most likely use diodes to switch in another trimmer or two.

In any event, if you've been putting up with QRM while listening to
the shuttle, the above adjustment might be worth it to you.

Later,
Marshall Jose  WA3VPZ
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