[GreenKeys] 88 mh toroids

[Richard Knoppow]

----- Original Message ----- 
From: <kf9nz at juno.com>
To: <greenkeys at mailman.qth.net>
Sent: Friday, June 17, 2011 4:56 PM
Subject: Re: [GreenKeys] 88 mh toroids


>                        All very true, except that what I 
> meant was, how
> they were used in RTTY.   They were used to create two 
> audio frequency
> tune circuits; one mark and one space.  Toroids have very 
> high Q which is
> needed to make a tuned circuit narrow enough to give good 
> selectivity at
> audio frequencies 150 to 300 Hz apart.
>                        As for the original use of loading 
> coils in
> telephone circuits, it has gone the way of the vacuum 
> tube.   My son-in
> law spent a lot of time in manholes cutting out loading 
> coils in toll and
> exchange cables, but these days there are very few toll 
> and exchange
> cables.  Now he spends time pulling them out of ducts so 
> fiber cables can
> go in.    A few years ago telco's were going crazy looking 
> for duct space
> in big city streets.  Now they could lease duct space for 
> water pipes.
> Telephone switching as I learned about it is ancient 
> history.
>
> Frankf9nz

    Probably twenty or more years ago I was on a tour of the 
local telco long lines terminal facility in downtown L.A. 
this was a little before the break up. They had recently 
replaced a lot of copper with multi-mode fiber and we were 
told that the scrap value of the copper paid for the new 
cables. Of course this stuff is probably all gone now 
replaced with single mode fiber.
     I do remember being able to buy 88mh toroids for very 
little for all sorts of purposes. I think when I saw plans 
for the first RTTY adaptors, in CQ magazine sometime in the 
late 1950s (?) they were not so readily available but there 
were sources.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com