[R-390] CV-157 SSB converter

Thu Feb 20 20:53:41 EST 2014

Gents,

The CV-157 demodulates fully suppressed carrier signals just fine with 
AFC switched OFF--but with one serious drawback (relative to other 
converters).  Its 555 kc LO, which is motor driven in AFC mode, is 
inherently much less stable than the oscillators in the companion 
R-390(*) receiver, and the entire receiving system's frequency stability 
is somewhat degraded as a result.  This is particularly true during the 
first half hour or so of warmup.  The CV-157 was really designed for 
pilot carrier AFC operation, with the transmitter's carrier level 
typically reduced 16-20 dB below PEP.  In AFC mode, the drift was 
relatively insignificant.

In the early 1960s when synthesized equipment began to proliferate, 
there was a big incentive to get rid of the wasteful pilot carrier and 
reallocate its power to additional sideband intelligence, and the 
stability problem became an issue.  The solution was the Manson 
Laboratories SBM-1 "Stabilization Kit" designed as an upgrade for the 
R-390A and CV-157.  A number of AN/FRR-41 systems were retrofitted with 
it, especially by the Air Force.  The system consisted of the Model  
299  Synthesizer, which provided a synthesized 2.455-3.455 in 100 cps 
steps for both 390As, and the Model 372  Stabilizer, which synthesized 
all the crystal injection points for the two R-390As, plus a synthesized 
555 kc and 100 kc for the two CV-157s.  The FRR-41, thus modified, could 
be then operated either fully synthesized, or with continuous tuning and 
pilot carrier AFC as originally, .  I have one of these updated FRR-41 
systems, and it works great, although the synthesizers are quite cranky 
and require frequent attention. The system I have was used by the 45th 
Space Wing as an ISB high speed computer data link on the Eastern Test 
Range in the mid 1960s.  This may have been the world's first computer 
wide area network--and on HF!  Later,  the enormous remotely-tuned 
DDR-506 receivers, developed by TMC, were used for similar purpose by 
NASA between NASA Goddard, Wallops, and the Range & Instrumentation 
ships during Project Apollo.

But back to the CV-157.  Other than the matter of stability, it's a 
great piece of gear when it's working and properly aligned (which is a 
bit of a chore).  The main problems seem to be failed crystal filters 
(usually LSB, for some reason), and failed power transformers (usually 
the high current filament winding).  Some crystal filters have aged 
badly and have poor response, though they haven't failed altogether.  
Carrier level meters tend to fail frequently, for some reason.  Of 
course, you have to reform all those electrolytics and replace a buncha 
toobs.  But when you're done, you'll have a marvelous piece of equipment.

BTW, a common misconception is that the CV-157 is a Collins design, a 
natural assumption given its obvious R-390-like appearance.  It was 
actually designed by Hoffman Laboratories in the early 1950s, based on a 
patent they held.  Three companies seem to have made them, Hoffman 
(early units), Dubrow Electronic Industries (late 1950s), and Bridge 
Electronics.  Bridge seems to have made the largest quantity, on a 1962 
contract.  Collins never made any.  I don't know how many were made, 
although it was obviously a tiny fraction of the number of R-390/390As 
produced.

Please keep us all informed of your adventures as you dig into those 
CV-157s!

73,

John K9WT

On 2/20/2014 4:48 PM, Bill Hawkins wrote:
> That's a good source, Norm.
>
> The manual says the 157 was designed to recover both upper and lower
> sidebands.
>
> It does not clearly state that these are sidebands of a suppressed 100
> KC carrier.
>
> *** Has anybody used one of these on the SSB signals available today?
> ***
>
> As the manual says, the 157 was designed to provide the equivalent of
> two multiplexed telephone lines to channels A and B.
>
> Maybe a channel can deliver a plain telephone voice signal. Really don't
> know if it works without the 100 KC carrier.
>
> The control labeled AFC that looks like a circle with two dots on it is
> actually a disk driven by a motor shaft that turns a variable capacitor
> that trims the local 100 KC oscillator to match the received 100 KC
> suppressed carrier.
>
> Like so much of what Collins did, it was the peak of what you could do
> with vacuum tube technology at the time.
>
> Bill Hawkins
>
> -----Original Message-----
> From: Norman Ryan
> Sent: Wednesday, February 19, 2014 6:09 PM
>
> This link looks like as good as any -- a nice clean pdf copy:
> http://www.militaryradio.com/manuals/CV-157/cv-157-tm11-266.pdf
>
>
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