elric@proper.UUCP (Elric of Imrryr) (05/14/86)
<><><><><><><> Due to increasing phone problems, and a bad modem.. I need HELP! Does anyone know where I can get an inline telephone amp? The carrier I get from 'proper' is just at my modem threshold, and the amp would really improve my line quality. qantel!proper!elric lll-crg!dual!proper!elric ucbvax!dual!proper!elric
larry@kitty.UUCP (Larry Lippman) (05/18/86)
In article <235@proper.UUCP>, elric@proper.UUCP (Elric of Imrryr) writes: > Due to increasing phone problems, and a bad modem.. I need HELP! > Does anyone know where I can get an inline telephone amp? > > The carrier I get from 'proper' is just at my modem threshold, and the amp > would really improve my line quality. Most modems have a carrier detection threshhold of no less than -37 dBm. "Better quality" modems (like AT&T, Rixon, Vadic, etc.) have threshholds as low as -45 dBm. Assuming a modem (which you call) transmits its carrier at -10 dBm, your modem should be able to tolerate at least a 27 dB loss between your subscriber location and the subscriber location of the called modem. Most DDD telephone connections in the continental U. S. will result in less than 27 dB overall loss between subscriber locations (we hope!). Adding an amplifier to a standard subscriber telephone line at the subscriber location presents some formidible problems. Due to the bidirectional nature of the required "amplifier", and the fact that the "amplifier" needs to pass DC signalling and ringing, only a device known as a "negative impedance repeater" would be satisfactory. Negative impedance repeaters (E-type and hybrid-type) are used by telephone companies for subscriber line loss reduction, but these devices are located in the telephone central office. Installation of a negative impedance repeater is NOT a trivial task, and requires knowledge of the EXACT transmission characteristics of the GIVEN subscriber loop; i.e., resistance, capacitance, cable gauges, nature and spacing of loading coils, etc. This sort of information is not readily available to the average subscriber. An IMPROPERLY installed repeater is more of a curse than a blessing, since it can result in: "singing" (feedback squeel), severe transmission non-linearities (loss plotted against frequency), etc. So what can you do? 1. Forget about any amplifier or repeater. 2. Have your modem checked for sensitivity; perhaps it is defective and running at decreased sensitivity. 3. If you believe that your voice transmission is low, complain to your telephone company and have them check your line for loss FROM YOUR PREMISES. DO NOT tell them you are having trouble with a modem; a telephone company will not guarantee suitable data transmission over an "ordinary" (which I assume you have) subscriber line. The telephone company may want to charge you for a service call, but if you are clever, you should be able to avoid this. :-) :-) :-) 4. Minimize the number of ringer loads on your telephone line while using your modem; each ringer load attenuates transmission (while not a hell of a lot, they do add up). 5. If you know the person or organization at the OTHER end of the connection you are having trouble with, ask them to check the transmit level of their modem, and possibly their telephone line. ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP {bbncca|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE 716/688-1231 {rice|shell}!baylor!/ ==> FAX 716/741-9635 {G1, G2, G3 modes} seismo!/ ==> "Have you hugged your cat today?" ihnp4!/