[ARC5] interesting ?

[Michael Hanz]

On 2/23/2018 4:28 PM, Roy Morgan wrote:
> Am I right in assuming that these things (the Ebay frequency 
> converters) preceded the APR-4 and APR-4Y?

Slightly (mid 1943 versus early 1944), but definitely not the APR-4 
predecessors mentioned below, which were all derived from the General 
Radio P-540 microwave receiver.

> THE APR-4's were in use in the 50's into the 60's I would guess.
> I have where I am an APR-4Y (which runs on 400 - 800 cycles) but I 
> think no plug-ins.
> Elsewhere I do have some plug-ins for this thing.  I may have to lash 
> up a big audio amplifier to run it.

If you have a hefty 28v power supply, you might look for 400~ aircraft 
inverters.  Occasionally you will find one for a reasonable price.  The 
APR-4 takes about 110 watts of 400~ power.  I have found them at 
hamfests for $5 to $10.

> These things are interesting to me because they originated from a 
> General Radio device meant to be used with slotted lines and the like 
> that produced an "IF" frequency of 30 mc. It *may* have been an MIT 
> Rad Lab project to upgrade the GR thing.

Yes to both subjects you raised.  Dr. Alfred Price, for his Doctoral 
Thesis in 1985, documented an interview he had with Dr. Don Sinclair:

"At about this time [circa late 1940] Dr. Don Sinclair, a Canadian 
working with
the General Radio Company at Cambridge, Massachusetts, began
work on the receiver portion cf a field strength measuring set
intended to cover the band 100 to 3,000 MHz. To achieve the required
broad tuning range, the receiver used the novel ' butterfly' tuning
device which Sinclair himself had invented. It soon became clear that
the unusual receiver might be suitable for a role quite different from
that for which it had originally been intended, however, and in July
1941 the Radiation Laboratory placed an order with General Radio
for prototypes of an intercept equipment based on Sinclair's
receiver. The device, which received the General Radio prototype
designation P-540, was to become the first purpose-built US radar
intercept receiver. During tests the P-540 continued to show promise
and the Army Signal Corps placed an order for a hundred receivers
of this type, now designated the SCR-587, with the Philco Corporation."

The SCR-587 was also nomenclatured by the Navy as the "ARC" (think ARA, 
ARB, ARD...etc.), and then quickly, the "ARC-1", with some minor (Navy) 
improvements.  By then, we were into 1943 and it was obvious that the 
587 and ARC-1 needed improvement, especially in the tuning area, which 
did _not_ have single knob tuning.  It was like tuning an early superhet 
receiver, with separate oscillator and RF amplifier dials.  The APR-1 
and APR-4 were the result of that need, but I would not call the APR-4 
an upgrade from the APR-1 - full scale production came about the same 
time in early 1944 for both - the APR-1 driven by Navy requirements, and 
the APR-4 driven by USAAF specifications. There were some IF step 
attenuation capabilities on the APR-4 that proved useful in the long 
run, so the APR-1 became another piece of flotsam in the sea of 
countermeasures receivers that became obsolete.  The APR-4 was 
re-nomenclatured again in the AN/ALR-5, this time with the CV-253/ALR 
tuning head, which covered 38-1000MHz in four bands and greatly improved 
sensitivity,and the 400Hz powered APR-4Y being the only changes,.  The 
other two APR-4 tuning units that covered up to 4GHz still worked in the 
mainframe.

What is lost in all this summary was the fever of research and rapid 
improvements in the hardware, pretty much on a monthly basis.  Talk 
about a release version documentation nightmare!

           73,
  - Mike  KC4TOS



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