[GreenKeys] We Co 255 Polar Relay

[KFIam640 at aol.com]

In a message dated 9/29/04 11:16:26 AM Pacific Daylight Time, 
donmehl at comcast.net writes:
                The  use is as a repeater.  The teletype machines require a 
60-milliampere neutral current to operate the printer.  Neutral means that 
positive current would flow for a mark or no current for a space.  A polar signal 
uses a positive current for a mark and a negative current for a space.  On 
longer wire line circuits polar operation is used.  The relays convert the signal 
from polar to neutral when required and also provides the 60-milliampere line 
current for operating the printer.  On long circuits the line current was 
30-milliamperes.   Distortion and deterioration of the signal over long wire 
lines are removed by the relays so that the printer will operate properly.  The 
relays would also be used as repeaters at relay points to extend the distances 
beyond 40 miles.  
I would like to offer a word of caution regarding use of a polar relay if you 
are going to be receiving RTTY radio signals.  Years ago I had a polar relay 
in my receiving setup.  I soon found that the arcing of the contacts as the 
relay keyed the 60 ma loop interfered with receiving weak signals.  After that 
experience I have stayed away from polar relays and relied on either a tube 
type or solid state type 60 mA loop keyer.  The softer switching of the tube or 
transistor keyer eliminated the interference generated by the polar relay.

Marvin, W6OQI