[GreenKeys] RTTY receiver noise immunity

Wed Apr 21 14:06:45 EDT 2021

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

On Wed, Apr 21, 2021 at 10:45 AM Don Cunningam <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
>
> 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
>
> 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> 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
>
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