[GreenKeys] Grounding lines in 60ma loops

[Harold Hallikainen]

Flesher TU-170 has internal loop supply with negative side ended. Current
is set using an active current sink transistor between the loop and
ground.

The DSP TU (https://w6iwi.org/rtty/DspTU2/ ) has a floating loop
interface. It does not care about ground or polarity. It looks a bit like
a printer with selector magnets in series with a keyboard.

I really like isolated loop interfaces!

Harold
https://w6iwi.org



On Sun, December 3, 2023 12:35 pm, Nick England wrote:
> As usual, I'm sure I'll screw something up so additions and corrections
> are
> welcomed.
>
> When hooking up multiple units to a multi-loop patch panel it is possible
> to inadvertently short something out because a connected device has one
> side of the line grounded.
> Typically the minus side of the loop supply will be grounded and that is a
> return for all loops. Each loop is fed by the positive side of the supply
> through a current limiting resistor and then through the LOOPING jacks and
> then the SET jacks (TTY printer, TD, reperf, etc.) and then to the LOOP
> DEVICE (keyer/converter/etc.) and then back to minus/ground. This
> arrangement works if NO LINE TO A TTY IS GROUNDED
>
> A note from hard-won experience - some TTY sets are polarity sensitive -
> M28 RO, KSR, and ASR may have a LESU with a line relay or selector magnet
> driver - you must apply proper loop polarity to the line inputs. Western
> Union devices might have one line grounded and you'll need to isolate
> that.
>
> Some RTTY converters and modems have isolated loop inputs and outputs but
> many do not. Here's a quick list of what I have found -
> FSK Receive Converters (with internal loop supply)
> Dovetron - negative side of loop is ground
>
> FSK Receive Converters (no internal loop supply)
> AN/URA-8A, 8B (CV-89) - switches loop (pin A) to ground (pin B)
> AN/URA-17 (CV-483) - switches loop (pin A) to ground (pin B)
> AN/URA-17A (CV-483A) - switches loop (pin A) to ground (pin B)
> AN/URA-17B (CV-483B) - switches loop (pin A) to ground (pin B)
> AN/URA-17C (CV-483C) - switches loop (pin A) to ground (pin B)
> AN/URA-17D (CV-483D) - switches loop (J8/A) to ground (J8/B)
>                      (or for a negative loop switches J8/C to J8/B)
>
> FSK TU receive/transmit (no internal loop supply)
> AN/SGC-1 -
>      SEND/RCV loop isolated (TTY+, TTY-)
> AN/URA-17E (CV-3510A)
>      SEND loop isolated (+loop J5/A, -loop J5/B)
>      RCV loop isolated (+loop J8/A, -loop J8/B)
> AN/URA-17F (CV-3510B)
>      SEND loop isolated (+loop J9/A, -loop J9/B)
>      RCV loop isolated (+loop J6/A, -loop J6/B)
> CV-2460
>      SEND loop isolated (+loop TB1/6, -loop TB1/7)
>      RCV loop isolated (+loop TB2/5, -loop TB2/6)
>
> AN/URC-32 transmit keyer (+loop TBD/1, ground TBD/16
> AN/URT-23 transmit keyer isolated (+loop J7/B, -loop J7/C)
>
> Note - I believe that all low level devices have one side grounded and the
> other is signal with +/-6v signaling.
>
> Nick England K4NYW
> www.navy-radio.com
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