Hello everybody It's nice to see our product detailed description from third body. How did he got our equipment at his office?
David Drori wrote: > > Dear Treggers, > > The following remark by Joe Randolph relates to the seemingly odd DC > requirements at low DC currents, stipulated by both TBR21 and by the > German Standard (BAPT 223 ZV 5): > > "I too have noticed the problem that you cite regarding the DC V-I test at > extremely low loop current. I have no idea what the technical > justification > is, but I note that this requirement is similar to one that appears in the > German requirements." > > I believe that I can shed some light on this subject. Here in Israel, use > is commonly made of a pair gain system that allows two separate telephone > numbers to share a single copper pair. This system is installed when a > subscriber wishes to add a second directory number, but the number of pairs > to that subscriber's location is limited. The system is a 2-channel PCM > coding and multiplexing device, with a demultiplexer at the subscriber's > end. We happen to have such a device (manufactured by Tadiran > Communications) installed in our own office. In the course of our work, we > test all kind of designs on our office lines, and during these tests, we > have observed that the on-hook voltage of our telephone lines is around 32 > volts and the apparent on-hook line resistance is approximately 150 kilohm! > This value was measured by connecting a 100 kilohm resistor in parallel > with the line, which causes the line voltage to drop to around 12 volts. > Naturally, if the line is terminated with a lower resistance, the > demultiplexer registers a valid off-hook state, and provides a line, at > which stage the apparent (off-hook) line resistance becomes a much more > conventional value. > > If this isn't reason enough for specifying the DC characteristics down to > extremely low DC currents, then I don't know what is! I have to assume that > equipment of the type I have described, and possibly other devices too, are > also in use in Germany, and that they are the reason for the low-current > requirements. Such systems clearly work imperfectly if the subscriber's > equipment fails to behave in the expected manner during the on-hook to > off-hook transition at low DC currents. > > I would not be at all surprised if such systems are being used in countries > outside Israel, and that -- apart from Germany -- the regulatory bodies are > simply uninterested in specifying terminal equipment accordingly, or might > even have failed to notice the need! Here in Israel, I know that most > imported equipment is designed to meet FCC Part 68, and to the best of my > knowledge, does not have to pass any special test for DC response at low > currents (although Bezeq -- Israel's very careful and professional national > telephone company -- does specify the V-I curve down to 0 mA for telephone > sets that it buys for distribution to its customers). I can well imagine > that some subscribers are experiencing technical difficulties because of > incompatible equipment both in Israel and in other countries. This would > manifest itself as a malfunction in which the user lifts the handset (or a > telephone answering machine or modem, etc., attempts to signal off-hook), > but no dial tone is returned, and the sidetone is negligible or > non-existent. > > I hope that it is now clear why the Germans are probably so keen to > maintain a controlled transition to the off-hook state at low DC currents. > > As an afterthought, I would venture to express my own opinion that all > regulatory bodies should be required to justify their Standards with > technical explanations, for their own and everybody else's benefit. This > should be standard engineering and documentary practice, and should be part > of their ISO9000 documentation. Failing to do so creates ill feeling > amongst designers and manufacturers, has everyone guessing the resons for > apparently idiotic requirements, and brings about the creation of often > misguided lobbies that waste everyone's time. If anyone on ETSI (or indeed > on any Standards-generating commission anywhere) reads this or receives > this, he or she might like to address this proposal, and make it a part of > the process of creating the pan-European norms and requirements. > > Best regards, > > David Drori > > --------------------------------------------------------------------------- > ------------------ > Novarex Enterprises Ltd., > POB 2833, > Jerusalem 91028, > Israel. > Tel: +972 2 581 0995 > Fax: +972 2 581 3750 > Mobile: +972 5 067 8686 > E-mail: [email protected] > --------------------------------------------------------------------------- > ------------------ -- Best Regards Chaim Geva Product Qualification Manager Access Systems Division Tadiran Telecommunications Ltd. Tel. (972) 3 9262822
