[Milsurplus] A New Concept: Virtual Spectrum

[w8au@sssnet.com]

At 07:11 PM 10/14/2003, William Donzelli wrote:
> > Actually, the "data" exchanged by Carrier Current transmission over High
> > Voltage
> > lines as early as 1926 (GE Carrier Set CC-3) was strictly AM voice.
>
>Sounds very neat. The information I have is for a Westinghouse system,
>and I am pretty sure it is somehow based on tones. Very cool looking bit
>of gear - a rack with a HUGE insulator on top.

This "insulator on top" would be unusual.  It might have predated
the conventional 50 ohm feed to the "underground" (coax running in covered
trenches) out to where the RF was applied to the HV line by use of
impedance matching.... (aka: antenna tuners) where it was transformed
to the approximate 400-600 ohms of the HV line.

The very earliest method of coupling RF to the HV line was by running
what we would call "gimmick capacitors" for about 1500 feet parallel
to the particular line.  (Spaced far enough away to avoid arcing, of course)
This method could have been used to tie directly to that insulator
you speak of.   This early method of coupling was abandoned because
it afforded very little lightning protection.  Later on, (and today) the
coupling is by series stacked HV caps (on a pedestal) dropping down into a 
tuning
box that has a "drain coil" to shunt the 60 Hz high voltage to ground.
We electronics types call that an RF choke.  The impedanced matched
RF is then coupled to the stack capacitor just above the drain coil (RFC).


Westinghouse and GE both were the main suppliers of Carrier Current gear.
Westinghouse gear always looked neater to me since it was mainly painted
black crackle, just like their MIL gear.   GE used mainly flat 
grey.   Perhaps GE
never mastered black crackle painting.... witness their TCK "flakers."

>I wonder if anyone tried running a Teletype thru the CC-3 box, using FSK?

I can't say that some Utility did not use tone keying or even FSK to run a
teletype system, but I know of none and never saw any manufacturer's
advertising promoting it.

Some of the early TTY use by utilities was by telco connections using DC
on-off keying.  If the circuit covered a huge number of miles, the DC was
converted to FSK or AFSK at telco central offices (using telco carrier current
systems running on their own cables) and then converted back to DC
at the final  CO (central office) to feed the local line to the user.

Otherwise, GE's Carrier Current "telemetering" sets (forties/fifties) used 
FSK, and this
could have been adapted to RTTY, for sure.

Later uses of AFSK plug-in tone modules, built by GE and Quindar, from
the fifties onward, allowed teletype operation using telco connections
or microwave basebands.   This is not to say that some Utilities did not
try the same thing by modulating a Carrier Current TX..... it sure would
have worked.

You know how it goes.... if someone had a great idea, even
if not supported by commercial manufacture, it was probably done.

Perry