[Milsurplus] RAS Noise Limiter

[Nick England]

RAS noise limiter CKB-50142 Manual -
https://www.navy-radio.com/rcvrs/ww2/ras/ras-limiter-man.pdf

I found this interesting info from the testimony of Hoffman's chief
engineer in a trial (Mission Bell changed its name to Hoffman)
(Testimony of Walter S. Harmon.)
"We had an item which was known as the noise peak limiter adapter. If we
want to speak of inventions or original design, that definitely was,
including constructing a complete unit which was conceived by us in its
entirety. The purpose of the equipment was to limit noise peaks on
communication receivers. The theory behind it was by certain circuit
configurations we could make the receiver respond to wave forms of pure
sine wave, which normal communications signals are. Noises are random wave
forms; by that I mean they are not a pure sine wave. I don't know whether
anybody knows what a pure sine wave is or not, but anyway, that is a wave
of uniform shape, whereas noise peaks are a random form. To put it plainly,
the idea was that you could not take a square block and put it through a
round hole.

Now, that is essentially what the noise peak limiter was. As I say, it was
originated by Hoffman Radio Corporation and submitted to the Navy
Department and subsequently ended up in a small production contract, I
believe the figure was 2280 units. [note - this is the correct figure for
the CKB-50142]

We also produced along that same line an electronic relay. Again the
purpose of the relay was to limit noise. That was adaptable only to
communication receivers, not receivers using voice frequencies, but rather
code frequencies or code signals, I should say. That was developed by us
and offered to the Navy Department as a new development. It was very
effective. Tests at the Naval Research Laboratory indicated that noise
reduction was in the order of 120 decibels. 120 decibels means that that
was a million to one ratio. In other words, to give the same amount of
sound from the receiver the noise had to be a million times stronger than
the desired signal, which for all practical purposes means there was no
noise, in that your ear could not differentiate between a million to one
ratio in sound. There was a great deal of pure development work went into
that device. It did fill a need.

The Navy Department first issued a development contract to produce 10 of
these units. I don't recall just where they were sent. I know of one unit
that was sent into the Alaskan area, where they were troubled with very
heavy static, another went into Honolulu, which was another noisy area, I
believe one went into Florida; the rest of the 10 I am not sure where they
went, but anyway they were shipped into areas where noise was a factor, and
the field tests showed that the instrument was very effective. I think
later that ended up in a production order for a redesigned unit. However,
it does not come into the period with which we are concerned.

On this noise peak limiter we also developed, as I recall, three different
types. One was made as an accessory for the Navy—I believe it was the RAS
receiver. Another one was made for the SX-28 receiver. Still another one
was made for the ARB. The purpose of all of them was the same, just a
matter of adapting them to receivers.

Now, that was an accessory that could be sent out into the field where they
had noise and they had a certain type of receiver. This adapter could be
plugged into the receiver, and it was very effective in reducing noise,
which means that communication was made possible in some cases where it
would not have been otherwise."
==============================
Nick England K4NYW
www.navy-radio.com


On Sun, Oct 15, 2023 at 3:01 PM Ray Fantini <RAFANTINI at salisbury.edu> wrote:

> RAB was one of the first super-heterodyne out there and a great example of
> what the newer technology as compared to TRF had to offer, but when the
> HRO, not as much the RAS but the regular HRO rolled out look what it had to
> offer, not only a super het but also crystal filter in the IF and a working
> AVC system that used tubes built around the idea of applied AVC.
>
> The RAS was somewhat like a HRO jr. without filter or S meter but there
> was the very mysterious Noise Limiter modification kit where you removed
> the detector AVC tube and stuffed that small assembly in the radio and it
> eliminated all the problems that the radio had with lightning burst and
> other high impulse noise. The mysterious thing is that no one can
> adequately explain how it works!
>
>
> Ray F/KA3EKH
> _._,_._,_
>
>
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