Chuck Manetta N4YJC August 5, 1991
To: All interested Amateur Radio operators!
On June 11, 1991 I sent out a Bulletin through the Packet Bulletin Board System to "RFI @ ALLUS". This Bulletin was titled "ANY ANSWERS TO PACKET / CABLE 18 RFI YET?". This bulletin was concerning the interference created by Packet Radio to the Cable Channel 18, and vice versa Cable Channel 18 to Packet Radio. The response to this bulletin was nothing short of incredible! In approximately one month, I received in excess of 50 replies from the United States and Canada! A number of these replies were from hams that were very interested in what helpful information I might have found.
This overwhelming response to this bulletin, showed me that there was a major adverse interaction between the Cable Industry and the Amateur community. This caused me to research this problem with more vigor. The answers apply to all amateur VHF operation, in all modes.
I would like to give credit to all of the Amateurs and Professional Consultants who have helped me research this area of interest: KY6V WB6KGB KB4FOW KA4OPZ N4LDG KP4OO KB4RLL N4VDM N4KWB N4UTO WD8KCT KG6XX KC4IEE WD4DPH KN4QH WB6CBJ WB2NGZ WN4ISX KC4WTX KM4ID KA7CGB KG7FU KA9NME WA2RCB WD4LYV KC2FD WB5BBW N5LDD K2TNN VE7BLZ AA9AW VO1MQ N2KZH VE7CJT VE7HGN N5HOF K0FPC WA2ZKD N8AHK N2DS W0BQH NJ8J KB5MGE W1CDM W9IUP N1CB W4NTG WB7NNF N7MWA KA4JEE WV9J W5NDG N7HFZ K6RAU KB6CYS
Ed Hare KA1CV, Senior Laboratory Engineer for The American Radio Relay League.
Gordon Smith KY6V, Chief Engineer for WCIX, Channel 6 Television. Miami Florida.
Ray Vaughan KD4BBM, Technical Manager (Cable Engineer Certified by The Society of Cable Television Engineers and The Society of Broadcast Engineers), Dynamic Cablevision of Florida. Roger Holbeg, Supervisory Attorney, Mass Media Bureau, Enforcement Division of The Federal Communications Commission. Washington DC.
Michael Lance, Electronics Engineer, Mass Media Bureau, Cable Television Branch of The Federal Communications Commission. Washington DC.
Engineers and Personnel from The Federal Communications Commission, Field Operations Bureau. Miami Office. Thank you all for your help and guidance!
Interference to cable-TV channels from amateur VHF operation. The problem exists because the cable-television spectrum covers a wide frequency range. It starts down in the low end of the VHF range and continues on through the UHF range. This spectrum, as you know, also includes a number of amateur bands! In theory, the cable system is supposed to be a "closed" system. By "closed", I mean entirely enclosed in shielded cable. No cable leaks out, and no amateur radio leaks in! But in reality we find that this is not true. There are many areas of improper shielding, loose connectors, substandard coax and even the possibilities of RFI or EMI (Electro-Magnetic-Interference) radiating through the cabinets of your TVs or being introduced into your TVs by the cable coax shielding itself!
As amateurs, before we start any investigation into the causes of a case of cable TVI, we should first make sure that our shack is clean. Make sure your equipment is properly grounded. Make sure that your TNC is not over-deviating your radio. Check that your transmission lines are in proper condition. If necessary, apply the needed cures to your own cable-connected television system. This demonstrates that the cures used do work and that they cause no harm.
(Continued in Part 2)
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