[Hallicrafters] DD-1 Audio amplifier |
Richard Knoppow
1oldlens1 at ix.netcom.com
Fri Feb 24 15:50:49 EST 2012
----- Original Message -----
From: "Joe Connor" <joeconnor53 at yahoo.com>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; "Duane
Fischer, W8DBF" <dfischer at usol.com>; "Waldo Magnuson"
<magnuson at mac.com>; <Hallicrafters at mailman.qth.net>
Sent: Friday, February 24, 2012 12:34 PM
Subject: Re: [Hallicrafters] DD-1 Audio amplifier
Here's a fascinating article on the DD-1:
http://www.radioblvd.com/DiversityDD1.html
Joe Connor
Fascinating! Its possible to adapt many receivers for
diversity. You need two of the same receiver and must
provide access to the AVC and detector load. The SP-600-JX,
especially the JX-17, came with the necessary connections.
The JX-17 allows the use of an external LO source which
keeps both (or more) receivers synchronized. Its helpful if
the overall gain can be trimmed so that one receiver does
not dominate the combination. There are special diversity
combiners which provide more sophisticated switching from
one to another signal. The crude arrangement possible with
the SP-600 simply ties the two AVC busses and detectors
together, which ever has the loudest signal predominates but
the other signal is still present. A true diversity combiner
switches from one to the other.
The article above gives a good survey of the history of
diversity systems but I think does not mention some other
anti-fading techniques such as the steerable antennas
explored by Bell Labs. These were based on the discovery
that the vertical angle of incoming radio signals varied
with time so that a significant improvement in reliability
could be achieved by making an antenna whose vertical angle
could be steered to follow it. I am not sure these "MUSA"
antennas were very widely used but they were described in
detail in the Bell System Technical Journal and, I think, in
the Journal of the IRE. I don't have citations readily
available but suspect a Google search might find some.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com
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