Path: utzoo!telecom-request Date: 15 May 91 03:55:50 GMT From: Paul Sutter Newsgroups: comp.dcom.telecom Subject: DAA Help Needed Message-ID: Organization: Apple Computer Inc., Cupertino, CA Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 372, Message 8 of 8 Lines: 33 Three DAA questions: 1) FCC Part 68 says the dc on-hook impedance should be 5 megohms. EIA-470 says at least 25 megohms. Which should I follow? iI is much easier for me to exceed 5 megohms than 25. 2) Many DAA circuits I have seen include the following surge protection: (tip) ----/\/\/\/\/----+-------- | (varistor) | (ring) ----/\/\/\/\/----+-------- With 5 ohm resistors, how are the wattage ratings determined? I have seen anything from 1 watt to quarter watt resistors used. likewise I have seen variation in the varistor used. Since these are for surges, how do you calculate the necessary ratings? 3) Can anyone suggest a cheapo transformer with 1.5kv isolation that does not have to be beefy enough to pull the DC offset? The cheapest we have found was a Midcom for $.80 (in moderate quantity), but since it was designed to pull the DC offset, I suspect a cheaper/smaller one may be found. Any suggestions? Thanks. Paul Sutter (not writing on behalf of my employer)