[GreenKeys] RE: GreenKeys Digest, Vol 59, Issue 39

Tue Dec 30 05:03:31 EST 2008

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Subject: GreenKeys Digest, Vol 59, Issue 39

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Today's Topics:

   1. Re: What is a polar relay for? (Jeffrey D Angus)
   2. Re: What is a polar relay for? (WA5CAB at cs.com)
   3. 2008 Bell Reunion T Shirts available... (Don Robert House)
   4. Polar relay (amourdutigre)

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Message: 1
Date: Mon, 29 Dec 2008 22:27:42 -0800
From: Jeffrey D Angus <jangus at socal.rr.com>
Subject: Re: [GreenKeys] What is a polar relay for?
To: greenkeys at mailman.qth.net
Message-ID: <4959BF5E.9020503 at socal.rr.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

amourdutigre wrote:
> I keep seeing something called a polar relay being referred to.

The magnets in your TTY machine, and most "normal" relays are operated
by on and off current. Or what is called "on off" keying. The selector
magnet
in a TTY machine is normally "unenergized" in the space position. And when
energized it is in the mark position. Typically with 60 ma of current to
cause
it to actuate.

In a polar circuit, it has three states. On one way, on the other way,
and off
(in the middle) which is sort of a disallowed condition.

For example, 20 mA positive current causes the relay to close in the mark
condition. Reversing the current in the opposite direction causes the relay
to swing over to the space condition.

The idea behind polar keying was to require current to be flowing for both
the mark and space signal, not JUST in the mark condition. And of course,
the lack of any current was detected and acted upon as a fault condition.

Jeff-1.0
wa6fwi

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Message: 2
Date: Tue, 30 Dec 2008 01:39:20 EST
From: WA5CAB at cs.com
Subject: Re: [GreenKeys] What is a polar relay for?
To: amourdutigre at kc.rr.com, greenkeys at mailman.qth.net
Message-ID: <c1a.4cf1e168.368b1c18 at cs.com>
Content-Type: text/plain; charset="us-ascii"

Joe,

An ordinary DC relay uses some mechanical means, usually a spring, to set
the 
OFF state of armature in the relay.  Running the proper current through the 
coil changes the relay to the ON state.  Turn the current off and the relay 
returns to it's OFF or resting state.  A polar relay armature moves one way
if 
the current is of one polarity and the other if the polarity is reversed.  A

polar relay (or at least some of them) can also be keyed by a neutral
circuit if 
it has a bias coil to set the OFF state of the neutral loop.  They were 
commonly found in Teletype sets into the 50's, and in things like
regenerative relay 
units or repeaters.

It is incorrect or misleading to say that a polar relay reverses the
polarity 
of a landline.  Reversing the polarity on the landline switches the polar 
relay.  Although you could certainly use a polar relay to do the line
reversal, 
you can also use a normal DPDT relay to do it.  But the normal DPDT relay
would 
not be usable at the other end of the line.  It would just stay ON.

$100 is excessive.  They generally go for I'll say $10-$25 in as-is where-is

condition.  Freshly calibrated they would probably be more but few have the 
equipment to do that and some who do lack the time.

In a message dated 12/29/2008 11:19:56 PM Central Standard Time, 
amourdutigre at kc.rr.com writes: 
> I have a question that I really cannot find an answer for.
>   
>  In my readings about electromechanical TTY units, I keep seeing something

> called a polar relay being referred to. I googled this, and found that it
is a 
> device that can be used to revers the polarity on a landline telegraph 
> circuit (not the local loop). Also, most of what little I could find had
to do 
> with hand (Morse) telegraphy, nothing with TTY.
>   
>  I have even seen polar relays referred to in amateur RTTY material from
the 
> fifties and sixties.
>   
>  What were these used for? I found one (I guess, the seller called it a 
> "rolar relay, I suspect a mistype) on e-pay for well over a hundred bucks.
>   
>  Thank you in advance,
>  
> 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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Message: 3
Date: Tue, 30 Dec 2008 00:45:41 -0600
From: Don Robert House <k9tty at dls.net>
Subject: [GreenKeys] 2008 Bell Reunion T Shirts available...
To: greenkeys at mailman.qth.net
Message-ID: <00F056B9-879F-4D3C-9BD7-E3BB49E074D9 at dls.net>
Content-Type: text/plain; charset=US-ASCII; format=flowed

Thanks to the Riceguy for this eBay tip:

Western Electric, AT&T, Teletype, Lucent, ALU T-Shirts

item 270323375482

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Message: 4
Date: Tue, 30 Dec 2008 00:49:49 -0600
From: "amourdutigre" <amourdutigre at kc.rr.com>
Subject: [GreenKeys] Polar relay
To: <greenkeys at mailman.qth.net>
Message-ID: <002101c96a4a$cf5973c0$74731a41 at win06v5>
Content-Type: text/plain; charset="iso-8859-1"

Hi all,

Thankyou for the info. I was wondering what they were used for, and did not
quite get the info that I needed from Google. Found lots of neat pictures of
rooms full of landline repeater stuff from around the turn of the last
century, but only some arcane descriptions of what they were used for.

As you can tell, I am an electromechanical TTY/RTTY neophyte, and have lots
to learn! I cannot wait to get my first TTY unit so that I can get a "real
RTTY"  (as opposed to computer RTTY) QTH set up and on the air!

Thanks again and best of the new year.

Joe KB0TXC

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