[GreenKeys] RTTY receiver noise immunity

Don Cunningam donc at martineer.net
Wed Apr 21 14:59:28 EDT 2021 

You are welcome, Nick.  I know that the circuits we used on the ship 
were either used continuously, like you said, or were "call as you need" 
duplex shore stations.  No need to account for no signal status.  I 
don't know of a simple threshold add on, but sometimes it would be nice 
to have the added noise immunity of the actual military units.  I just 
wish that they had 170 cycle shift built in.  The HAL ST-8000 and 8000A 
do have more noise immunity built in, but probably not to the level of 
those units you have.

The equipment currently on my ship, USS Edson (DD-946) are of an era 
different than mine, late 80's equipment, so very little of what is left 
is even recognizable by me.  That's a shame, but no one is there where 
the ship is moored as a Vietnam ship example to return it to Vietnam 
status in the radio room.  I will visit it one day, take my ham gear and 
put it on the "Museum Ships on the Air" weekend.  One ham does it now, 
but I'd like to do that for one time too.  I'd alert the list, but there 
is no Teletype equipment on board anymore or any transmitter/receiver 
pair to use either.  That was a disappointment, but probably inevitable.
73,
Don, WB5HAK
Former NJRE op

On 4/21/2021 1:06 PM, Nick England wrote:
> Thanks, Don.
> There is another model of converter on board (CV-2460/UG) that appears 
> to have more noise immunity so perhaps they will switch to using that. 
> I've been digging through the manuals looking for a circuit that 
> balances out if noise causes equal energy in both mark and space 
> channels. With some luck it may be that these 35 year old converters 
> will trigger less with some re-balancing along with adjusting the 
> audio input level.
>
> There is a TON of circuitry to provide reliable reception when there 
> is a RTTY signal, but not so much attention paid to when there is just 
> noise. There is even a phase-locking sync clock to sample the 
> bitstream - that works for 7.00-unit code but not for 7.42 - drove me 
> crazy seeing the thing drop characters periodically until I figured 
> that out! That was back before I got access to a manual.
>
> The CV-3510B has a 3-bar LED indicator - mark, space, and noise. The 
> best I can tell so far is that there is a noise detection circuit that 
> drives that noise LED bar.........but doesn't do anything else useful!
>
> Thanks to the group for all the helpful info on how vintage converters 
> behaved and what your experience with them was like.
>
> Cheers,
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
>
>
> On Wed, Apr 21, 2021 at 10:45 AM Don Cunningam <donc at martineer.net 
> <mailto:donc at martineer.net>> wrote:
>
>     Nick,
>
>     You may have to "sneak" a HAL or Dovetron TU on board and make it
>     the operational TU, but leave signal to the other one so it will
>     look right.  I know it's not "original", but either has a
>     threshold control to prevent the falsing you are experiencing. 
>     Just a thought.
>     73,
>     Don, WB5HAK
>
>     On 4/20/2021 7:24 PM, Nick England wrote:
>>     Yes, I’ve been going over this with them. I made a video using a
>>     similar Navy receiver and the same model converter.
>>     https://youtu.be/fwMSE2hZNCk <https://youtu.be/fwMSE2hZNCk>
>>
>>     They are using a Navy R-1051/URR receiver and CV-3510A/UG or
>>     CV-3510B/UG converter. The CV-3510 has mark-hold for steady space
>>     or steady mark or no signal.
>>
>>     We are going through the tech manuals to see if there is some
>>     reason they should have better no-signal noise immunity. But
>>     these were really designed to optimize signal reception from a
>>     continuously broadcasting transmitter. Not for ham-type
>>     operating. The converters were normally used in pairs for
>>     frequency or space diversity. They also treat mark and space
>>     separately for in-band diversity. But all that is for reliable
>>     operation when there IS a signal. Also the converters originally
>>     fed crypto gear which then fed the teletype. Perhaps the crypto
>>     gear may have provided the equivalent of mark-hold in noisy
>>     no-signal conditions.
>>
>>     The CV-3510A manual is here
>>     http://www.navy-radio.com/manuals/ura17e-cv3510a-man-8705.pdf
>>     <http://www.navy-radio.com/manuals/ura17e-cv3510a-man-8705.pdf>
>>
>>     The CV-3510B manual is not publicly available.
>>
>>     Cheers
>>     Nick
>>
>>     On Tue, Apr 20, 2021 at 7:50 PM Tom Hunter <n3crk at hotmail.com
>>     <mailto:n3crk at hotmail.com>> wrote:
>>
>>         Just my two cents - Has anyone asked what receiver and RTTY
>>         converter they are using and considered what is possible with
>>         those?
>>
>>
>>         Tom N3CRK   HH 12177
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>>     -- 
>>     Nick England K4NYW
>>     www.navy-radio.com <http://www.navy-radio.com>
>>
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