Ian Jackson wrote:

In message , Michael A. Terrell
writes
Ian Jackson wrote:


I'm in the CATV industry, and I've just remembered that, many years ago,
I did see reference to 'vampire taps' as being the latest and greatest
for coaxial ethernet. That took me back to the early 1960s, when similar
tap devices were manufactured in the UK (by Thorn, I think). I may still
have one somewhere. Nasty things!


Here, they were called "Stinger taps" and I had an unused tap block and
stinger, along with the strand clamp and drop hook in my toolbox, until
at least 2001. It might still be around, but I haven't used that toolbox
in so many years that i don't remember. I brought it home the day i was
laid off, then I was declared disabled, and unable to work, so it has
been under one of my benches here at home, ever since.


They were real low grade ****. They were replaced by backmatched
taps when systems were extended past the original 12 channel systems in
the US. They caused mismatch problems, and wasted a lot of the signal
on the trunklines or feeders. They worked, more or less on systems with
just a few channels, and very few customers, but them, those people were
already used to ghosting and snow. They had all been pulled from the 17
systems around Ft Rucker by 1972, including a couple short haul feeds
that only had a couple channels.


Equally bad on ethernet I expect? Also, does ethernet require them to be
non-directional (ie just resistive tap-offs, with no directional
coupler)?


Actually, there are two types of coaxial networking that used 75 ohm
cable. The simple, small network like Dave describes below witch were
non directional, and one that is usually part of a community loop where
pairs of one forward channel, and one return channel are used for data,
with a heterodyne signal processor at the headend to upconvert the
return channel to a forward channel witch is built with back matched
taps.

This system predates the current cable modems, but used standard, off
the shelf CATV components to build a private WAN along with the RF
modems. Some were mixed systems, of RF fed to clusters of the simpler
coaxial networking. The first system like that I heard about was the
Ohio State University campus in the '70s or early '80s. Their private
CATV system connected all the buildings, then tied the existing, smaller
networks together. I met two of their IT people at a hamfest, and they
were bragging about their design, till I told them about the systems I
maintained for the US army, years earlier. There was no return channel
equipment on the market, so we had a pair of 12 channel 'Vicoa' (Later
called Coral) systems set up as forward and return to carry the weather
data from an airfield to the main base where it added to the other nine
forward channels that fed the classrooms and airfield ready rooms.

We also built the first emergency alert system into a CATV system
that took control of the civilian CATV service to the barracks and on
base housing. A custom made coaxial relay was added to the existing
system to seize control of the private system. The ETV studio was 12
channel, like the civilian system. A toggle switch (with a hinged cover
and a lead seal) would feed the same audio and video to all 12
modulators, and switch the remote relay so an alert could be spread, no
matter what channel a TV was on. After we proved the concept, it
quickly spread to other bases, and new builds of civilian systems. The
last system I maintained was a 36 channel RCA headend, in the early
'80s. It had the optional IF loop through and auxiliary IF input for
the alert system. The Audio and video was fed through a separate
modulator with a IF output amp, instead of a channel module. I rewired
the rack by strapping the loss of signal output to the relay control,
and connected diodes to isolate each channel from the emergency control
system. I also looped the emergency video through the local access
control room so I could flip one switch and feed the same signal to all
36 channels in an emergency.

The loss of signal mod caused a message to appear a half second after
the carrier dropped out from a TV station, or satellite feed. That let
the tech on night shift check the alignment of the converters after
stations signed off, at night.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida