[Hammarlund] ITT modified SP-600

[mrharisn at hughes.net]

My apologies for jumping in here, but my understanding also that these SP-600s were modified by Mackay Radio to incorporate a third mixer with switchable 430 or 480 kc injection, and driving a 25 kc 3rd IF output going to a separate unit with two L-C bandpass filters, one for 22-25 kc, the other for 25-28 kc, each with its own detector. This allowed independent sideband reception. T he antenna input was changed to balanced feed and BFO/AGC provisions were also added to allow diversity operation. 
----- Original Message -----

From: "Les Locklear" <leslocklear at hotmail.com> 
To: "Bob Camp" <kb8tq at n1k.org>, kgordon2006 at frontier.com 
Cc: Hammarlund at mailman.qth.net 
Sent: Friday, August 29, 2014 12:25:13 PM 
Subject: Re: [Hammarlund] ITT modified SP-600 

This was taken from the Hammarlund SP-600 models page: 

Another variant was the R-450/FRR-28. These were standard Hammarlund JX 
receivers that were modified by Northern Radio; USN stock no. F 
16-Q-112117-200, contract number Nobsr-52132, 19 December, 1950. These were 
designated SP-600-MX. Installed in a relay rack cabinet with a LS-187/UR 
speaker, AM-615/UR amplifier detector, KY-79 keyer, O-165/UR high stability 
oscillator, S-224/UR patch panel and an AN/URA-8 fsk converter-comparator. 
The X-tal frequency control at the top r.h corner was removed and covered 
with a Buships/Northern Radio order no. nameplate. Northern Radio located in 
New York City made many modifications available for SP-600's such as an IF 
gain control located where the dial lock was normally located. This was a 
very common military modification. 

Les 

-----Original Message----- 
From: Bob Camp 
Sent: Friday, August 29, 2014 12:20 PM 
To: kgordon2006 at frontier.com 
Cc: Hammarlund at mailman.qth.net 
Subject: Re: [Hammarlund] ITT modified SP-600 

Hi 

F.S. TELEG = Frequency Shift (Keying) Telegraphy. More commonly known as 
FSK. 

Bob 

On Aug 29, 2014, at 12:17 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> 
wrote: 

> Well, the data-plate associated with the BFO says, "MOD FOR I.S.B. AND 
> F.S. TELEG." 
> 
> I know that ISB is Independent Side Band, but what, exactly, is F.S. 
> TELEG? 
> Some sort of RTTY, I would suppose. 
> 
> Anyway, it is very interesting, and the receiver looks to be in excellent 
> condition. I wish we knew fuller details of the mod. 
> 
> Price is way too much for me, though. 
> 
> Ken W7EKB 
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