[Hallicrafters] DD-1 Audio amplifier


Lloyd Godsey kk7iz at cox.net
Fri Feb 24 20:13:36 EST 2012


Not to mention the Hammarlund AN/FRR-12

Thanx
Lloyd Godsey KK7IZ
kk7iz at cox.net 
480-620-7145
http://www.lloydsdipsydumpster.com/
http://antiqueradioarchives.com/


-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Carl
Sent: Friday, February 24, 2012 4:09 PM
To: rbethman; hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] DD-1 Audio amplifier

National had  a diversity model of the NC-183 around 1947 and Hallicrafters
SX-28's were used during WW2.

National also built big racks full of special diversity receivers under some
FRR-nn contract.

Carl
KM1H


----- Original Message -----
From: "rbethman" <rbethman at comcast.net>
To: <hallicrafters at mailman.qth.net>
Sent: Friday, February 24, 2012 4:21 PM
Subject: Re: [Hallicrafters] DD-1 Audio amplifier


> Long before the SP-600-JX series, there was a Northern Radio Diversity
> version of the SP-600 J-11(No X), that was on a Navy '51 contract.  It
> required two receivers and also the Northern Radio LMO to keep both
> receivers in sync frequency wise.
>
> I've got one, I've seen a few others.  One could select either the
> internal LO or the external LMO.
>
> Bob - N0DGN
>
> On 2/24/2012 3:50 PM, Richard Knoppow wrote:
>>
>>       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
>>
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