hardie (10/07/82)
Have problem with interference of a kind I have not seen reported before. I have an ADM5 terminal at home which I and my kids use to play rogue etc. My rig is in the same room and if I transmit, the phone line drops instantly .. much to the annoyance of my daughter (age 7) who happened to be on level 10 with a large chunk of gold!. This did not happen when TTY was HP2640 (in fact reverse problem - it produces prodigious amounts of RFI) and using the same acoustic coupler. Any ideas as to cause and, better still, a cure (cheap!). TNX + 73 Pete VE5BEL utah-cs!sask!hardie
karn (01/18/83)
Here's a book I can recommend to anyone interested in the details of interference troubleshooting: Interference Handbook, by William R. Nelson, WA6FQG, Former RFI Investigator, Southern California Edison Company. As you might expect from the author's former job, he is very thorough in his discussion of the myriad ways power distribution networks can cause RFI. His method is very similar to the one Peter Hardie used to find his noisy transformer. I got interested in the problem of power line interference by necessity (the usual route.) When I lived in Illinois, a dual 138kv transmission line passed my house 10 houses away. As it turned out, the poles near my house were not a problem, but the "corner towers" 1/2 mile away where the line made a Z turn along a road toward a substation. The symptoms were somewhat strange: slowly rising horizontal static "bars" on the TV, and intermittent broadband noise pulses ruining 2 meter SSB (especially Oscar-7 mode B) reception. During heavy rainstorms, the noise would go away instead of getting worse! Although Oscar-7 failed in the summer of 1981, and I subsequently moved to NJ without the problem never really being resolved, I was reasonably certain I understood the problem. Ground lines running across the top of high-voltage towers are there to take lightning strikes, which could occur as often as every day or two during the late summer in Illinois. Although the ground lines were firmly clamped to the towers on the straight runs, at the corners a double-loop "dead-end" was used, with no hard connection between the ground line and the tower. Significant amounts of current were induced in the ground line from the power conductors, and arcing occured at the dead-ends. When it rained, however, my theory is that it temporarily suppressed the arcing and the interference. Fighting power line interference can be an exhausting experience. I spent many hours on the phone, riding around with the Naperville Electric Co maintenance men, and in desperation, writing letters to the Mayor and the FCC, all with only partial success. The best medicine is preventative - don't live near a large power line!! Phil Karn, KA9Q/2
karn (01/18/83)
Two additions to my item on power line RFI: The Interference Handbook is published by Radio Publications, Box 149, Wilton, CT 06897, and is available through most of the ham radio distributors. I meant to say "Naperville Electric Dept" instead of "Naperville Electric Co". Part of the problem was that I was dealing with a small municipal agency who bought power from Commonwealth Edison and maintained the local distribution network. They were simply too small to afford the RFI specialists that large companies hire. Phil