* Crossposted to ELECTRONICS
                  AUST_MODEM

Hi everyone. I am currently working on a "home brew" radio link
which will hopefully link my home with the location of my BBS. Currently I
have a second "sysop line" which dials out from the BBS via a PBX
line and calls my place; I have a Trailblazer at each end. It would be nice
to have my phone line free for other things. :-)

For the radio link, I will have a "PSTN emulator". This presents
a DC voltage to the modem, just like a normal phone line. The Trailblazers
have a "continuous dial" or "continuous answer"
feature, which means that no human intervention is required to get the link
up -- they just keep trying until they connect.

Anyway, if you pick up the phone and listen to them talking to each other,
it's as if they throw packets back and forth. There is no continuous
carrier, just the chatter as they continously send packets back and forth
(even when there's no actual user data being transmitted).

I envisage that I will have problems with feedback, since PSTN lines
transfer audio in both directions via the same wire, but the link uses
discrete paths for each direction. In effect, there will be an audio loop:

                        <<<<<<<
                     ____  r l  ____
                 RX /      a i      \ TX
Trailblazer --------       d n       -------- Trailblazer
                 TX \____  i k  ____/ RX
                           o
                        >>>>>>>>

What I think might work is if I block the audio as each end is
transmitting. IE: While my end is sending a packet, suppress any audio
received. However, this will only work if the Trailblazers actually do
truly only talk "one at a time". It seems they do, but I don't
know for sure.

I'm not entirely sure why I've written this message, since I doubt anyone
can help me, but if someone knows the Trailblazer (or PEP) standard
intimately, I'd be interested to hear from you.

Cheers.

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