EDM Solution 4+4, Руководство по установке

Страница: 156 / 174

Appendix A
Telephone Anti-Jamming
There are many companies today importing American designed products that claim to have
Anti-Jamming and believe it or not, they push this feature as if it were a major break through in
control panel technology. Well this in fact is not the case at all as most control panels have
some sort of Anti-Jamming feature. We can go as far back as the early 1980's where even the
678 diallers incorporated a form of Anti-Jamming as a standard programmable option.
The important thing to note is that as most American designed products are primarily aimed at
their local market and telephone networks, when they are imported to Australia their anti-
jamming function does not perform as it should.
To clear up just what anti-jamming is and how it works needs some understanding of
Telephone Networks. In America either of the two parties (ie. the one who initiated the call or
the one receiving the call) can clear the line by placing the hand piece back on the hook. If you
pick up the hand piece again, dial tone will be received and you will be able to make a new call
immediately. This is not so here in Australia.
In Australia, only the calling party can immediately terminate the call. If you receive a call
from someone and hang up on them, picking the hand piece back up again to make a new call
only reconnects you to the original caller. It will not be possible to make another call until the
original caller hangs up or you hang up phone the phone for ninety seconds or longer. So you
see Australia is very different and needs a special form of anti-jamming to suit our telephone
network.
There are control panels on the market that after making a few call attempts which fail simply
hang up and wait for ninety seconds or so, in an attempt to clear the jamming incoming call.
This may work in some instances where the caller is not a genuine burglar and is not
deliberately trying to jam the control panel. With this simple method of hanging up for ninety
seconds we have not only delayed the alarm signal for this time but also the time taken for the
original failed call attempts which could easily total 4 minutes. This is bad enough in its own
right but even more disturbing is the fact that the initial failed call attempts allow for the
establishment of an audio connection between the would be burglar and the control panel.
Anyone with a little knowledge of alarm systems will be able to actually trick the dialler into
thinking it is talking to a base station thus actually clearing the alarm signal. Pretty frightening
when you thought the control panel you were using and recommending to your customers is
supposed to have anti-jamming.
At Electronics Design and Manufacturing Pty Limited we take anti-jamming very seriously
and have in fact devoted a great deal of time and money researching this problem. Our
engineers have come up with the best possible anti-jamming procedure known and patented
accordingly {Patent Number 571994}.
Our procedure is very simple and effective because we never answer the burglars phone call
and the Telecom Network will automatically clear an unanswered call in approximately ninety
seconds. This time will be even shorter if the call is originated through the Mobile-Net
Network where it will most likely be in the case of a true burglary.
Once the control panel detects that the phone line has stopped ringing it immediately loops the
line and makes its call therefore transmitting its alarm message successfully. The line is also
automatically disconnected from the telephones within the protected premises immediately on
an alarm condition by the control panel to further confuse the burglar and eliminate the
possibility of the burglar answering the call. As you can see, our method of anti-jamming will
in the worst possible case delay the alarm signal by ninety seconds but even more importantly
will never allow for an audio connection between the burglar and the control panel.
156
Solution 4+4
Installation Manual
ISSUE123.DOC Electronics Design and Manufacturing Pty Limited