Dave Mc Mahan <mcmahan@netcom.com> (06/10/91)
I have been given the task of figuring out how to connect our latest
product to the European phone system. The device I'd like to connect
is the receiver end of a simple 10 Baud modem. The other end is a
transmit-only box that sends 64 bits of data. The tone protocol is
meant to be quick and dirty, as it needs to be decoded via software
control. It doesn't have to be fast, just reliable.
I am in the process of getting our European representative to send me
a phone to modify. My approach is to disconnect the handset, place my
receiving device in parallel electrically with the earphone, and use
it. Is this legal? The transmitters can be located at any point in
Europe, but are most likely to be located in England and Germany.
These are the acoustically coupled units and I see no problems with
the local phone police about connection to their networks. The
receiving end will be in Brussels, Belgium. I have been told by our
rep that as long as we don't actually connect to the wall directly,
but instead make the connection after the isolation provided by the
base unit of the phone, we will be ok.
What I need to find out is:
1. What are the legalities of connecting my receive-only unit in
parallel with the earphone? Is this acceptable as long as I do it
AFTER the base unit isolates me and provides protection? Are there
other legalities I need to worry about? If so, who are the governing
bodies that may cause me problems and what countries are they located
in?
2. I want to make the connection using an isolation transformer to
protect me from any wierd ground loops between the computer doing the
receiving and the telephone system. What impedance is the earphone
most commonly used in Europe?
3. When I get the phone sent to me, I need to hook it up and play
with it to make sure it will work. What kind of DC current does such
a phone need to operate? Is it similar to a US phone? I plan to get
a power supply and set up my own little test network external to any
phone company, but would really like to interface the phone to a real
phone system (hiding behind the shield of our local company PBX to
protect myself, of course). Does this sound feasible?
4. Any other helpful info you can tell me or point me toward.
I have completed the US version of the receiver. We got a tape
recorder interface down at Radio Shack that allows us to tap into the
phone line and still be isolated. It's even FCC certified, which I
thought wasn't possible for something that provides direct electrical
access to the signal (after the isolation transformer) for
who-knows-what kind of application. It's a great little gizmo, and
well worth the $25. I wanted to get the equivilent thing for our
European version, but was told that this is not possible. I can make
an acoustic connection with the receiver, but would like to avoid this
approach if I can help it. Direct electrical connection is MUCH less
noisy and doesn't provide the distortion introduced by having to go
thru the headphone/microphone of the local end.
Thanks for your help. Please e-mail me directly by sending stuff to:
mcmahan@netcom.com
Dave McMahan mcmahan@netcom.com {apple,amdahl,claris}!netcom!mcmahan