I have some Adtran ISU-128 ISDN 'modems' that may be used
over twisted pair, without any other equipment. This means
they may be used over your own pair or a 'dry' alarm pair
(very cheap) from the telco. They may be used this way because
it's possible to set one up to provide clocking. Consumer grade
and many commercial ISU's do not provide clocking.
In any case, this will get your control signals back and forth.
For the audio, a pair of filters as sold for use in isolating a
telephone set from a DSL modem, on the same line, will
do the trick. So, all you have to add is a pair of line matching
transformers (8ohm to 600ohm), a pair of filters, and you're
good to go. You can even apply a small current for sealing or
to run a relay at one end.
Another option for the audio is to put an PeeCee at the remote
and and stream it over the digital connection. IMO, overkill,
but an option anyway...
I've 4 pair of these and will sell for $50/pair plus $9 for
shipping (or pick them up in 30114, Canton GA)
A full manual(pdf) is available at the adtran web site. Configuration
for the setup described above is under the section on 'leased lines'.
Plug ISU128 into the adtran search window.
These are surplus from the local telco and in good shape. They run
on 120VAC and have built in power supplies and all setup is by way
of front panel controls.
Thanks,
-Bob
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