[GreenKeys] RTTY receiver noise immunity?

[Roy Morgan]

Greenkeyers (and R-390A nuts),

The R-390A had a squelch modification, presumably supplied as original in some units.  It was installed in the spaces provided for it on the If module, I think.  The major parts needed were one tube, and a low-current relay, and possibly a different mode switch for the front panel. (It may be that the normal mode switch has the needed contact but is normally held out of operation by the stop plate.). Maybe there was an added squelch level control added to the front panel, but my memory is faint on that point.

Very likely there is a modification document that tells about this.

The relay needed has a coil of about 10,000 ohms resistance and is operated by the roughly 10 milliamp plate circuit of the associated 12AU7 (?) tube.  Such relays can be bought currently for $100 or more, thought they likely are not the sealed military grade as the originals were.  My security contractor seriously advises me to neither confirm nor deny that I have any such relays.

> On Apr 20, 2021, at 11:36 AM, Nick England <navy.radio at gmail.com> wrote:
> 
> I’ve been in a discussion with the USS Iowa guys about what to expect when there’s no RTTY signal just receiver noise. They are concerned because they get a bunch of garble when there’s no signal and the AGC turns up the gain. 
> 
> Note. This discussion is not about noisy RTTY signals but responding to noise when there is NO RTTY signal.

On a related thread here, and relevant to the USS Iowa:
Re: [GreenKeys] Re: Was: TWX/TELEX now: Analog Computers

As a young Midshipman in Navy ROTC, in 1967 I was on a rather old destroyer, The USS Massey.  
-The gunnery fire control system was the analog Mark I system. See:
https://en.wikipedia.org/wiki/Mark_I_Fire_Control_Computer
For a short but interesting description.  The thing operated with mechanical selsyns, potentiometers, and all sorts of dials and input cranks and knobs.
-The radar displays were the size of a small refrigerator and were loaded with 6SN7 tubes and a very big magnetically deflected CRT display tube

After a live firing gunnery event, through some mysterious and long forgotten maneuver, an empty brass shell casing from the 3”-50 naval guns found its way into my duffel bag.  Good heavens, that was 54 years ago!

Roy

Roy Morgan
K1LKY since 1958
k1lky68 at gmail.com
Western Mass