[GreenKeys] Grounding lines in 60ma loops

[Daniel Jones]

The TU-170 can be used with an external loop supply also.  That’s how I run mine with a PP-3494A/UG loop supply.  

Daniel 

www.K6YIC.com
DJones at K6YIC.com
HH#11973

> On Dec 3, 2023, at 17:07, Harold Hallikainen via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> 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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