Phoenix Modems Causing Interference.
Hello, all.
I am an Amateur Radio Operator ("Ham"), and came across the following news article. It was posted at the Web site of the American Radio Relay League, the primary Amateur Radio organization in the U.S.
I am neither long nor short PTEC, but I am an investor, and figured that you likely be interested.
Steve
Cooperation Curbs "Wireless Modem" Interference
NEWINGTON, CT, Dec 24, 1998--A maker of "wireless modems" and a cable TV company that's been installing the units
across the US have told the ARRL they'll do whatever it takes to keep them from causing interference to amateur HF bands.
The ARRL contacted the two companies after receiving reports from members of the Northern California Contest Club about
80-meter interference from the devices. The devices, manufactured overseas by Phonex Company of Midvale, Utah, operate
under Part 15 of the FCC's rules. This means that they may not cause interference to licensed services.
"Although the Phonex Company has complied with required FCC regulations, the ARRL has identified a potential interference
problem on the low end of the 80-meter band," said Phonex Senior Engineer Scott Bullock, KK7LC. "We have several hams
in our organization, and we do not want to cause any interference to any amateur band."
Wireless modems are first cousins to wireless telephone jacks used to provide additional telephone jacks without wiring. Both
are sold in pairs. One unit plugs into the telephone connection while the other serves as a telephone or modem jack; both plug
into convenient ac outlets. The carrier-current devices impose RF on the power line to transmit data back and forth in the
form of wideband FM.
Other units made by Phonex and sold as wireless extension telephone jacks under the GE, RCA/Thompson, and Radio
Shack brand names operate on 3.025 and 6.436 MHz, where they generally will not affect the ham bands. Unfortunately, the
Phonex wireless modems operate on 3.52 and 8.27 MHz. Cable giant TCI has been installing these units in some subscribers'
homes to make a convenient connection from the cable box to the telephone line to transmit billing information. They are also
available in computer stores for use with computer modems and digital satellite systems. Wireless jacks and modems transmit
a continuous carrier on the lower frequency, whether the phone connection is in use or not, and on both frequencies when the
remote line is in use.
ARRL Lab Supervisor Ed Hare, W1RFI, says the League received reports in mid-December about persistent interference on
the low end of 80 meters and on other bands. The interference, consisting of discrete, somewhat noisy and drifting carriers,
typically showed up around 3520 to 3530 kHz, but harmonics of these signals also have been reported as high as 20 meters.
An informal investigation in the Greater Hartford, Connecticut, area revealed several nonamateur signals, including some
carrying wideband FM voice transmissions. One signal heard in a residential neighborhood literally pinned the S meter at 60
dB over S9.
ARRL Lab tests verified that the devices pose a serious problem for reception on the lower part of 80 meters and possibly on
other bands because of harmonics. Likewise, the devices also are very susceptible to interference from signals on 80 meters
and probably on other bands.
FCC rules permit the unlicensed devices to radiate signals on HF of up to 30 m V/meter, even if it's on an amateur band.
Device operators--TCI in this case--must correct any resulting interference, however.
TCI Senior Engineer Tony Werner says his company is a responsible corporate citizen and intends to comply with FCC rules.
He said TCI plans to eliminate the 3.52 MHz wireless jacks it's installed "as expediently as possible" by replacing them with
3.3 MHz units or by running a hardwired telephone connection. TCI immediately will replace units that cause interference and
automatically replace other 3.52-MHz units during routine customer service. Werner said TCI also will use nothing but
3.3-MHz units in the future. In the meantime, hams experiencing harmful interference they believe is related to these devices
should contact their local TCI office. Werner said he expected it would be several weeks before service information is
available at local TCI offices. He says the 3.3-MHz replacement units will be available over the next few weeks.
Bullock, meanwhile, says that Phonex has made the necessary production changes to move the operating frequency of its units
to 3.3 MHz. If one of its units causes interference, he said, Phonex will retune or replace it. Hams can contact Phonex
Customer Service at 800-437-0101.
"Both companies have been refreshingly cooperative," said Hare, who--as his W1RFI call sign reflects--is the League's point
man for interference issues. "If every RFI problem that involves Amateur Radio could be fixed so quickly, I would probably
be out of a job."
Hare credits a lot of teamwork with resolving the wireless modems problem. Many hams were also involved, notably several
member of the Northern California Contest Club, ARRL Pacific Division Director Brad Wyatt, K6WR; ARRL's cable
industry contact Ron Hranac, N0IVN; ARRL Vice President Hugh Turnbull, W3ABC; and Roanoke Division Vice Director
Dennis Bodson, W4PWF. Turnbull and Bodson, both members of the ARRL RFI Task Group, helped with the policy
decisions to determine how ARRL should proceed.
"To me, this is the real strength of ARRL--acting as a coordinator for the best of our best as we collectively solve the
problems of Amateur Radio," Hare concluded.
Hare said hams with questions about this issue may contact him directly at ARRL HQ at 860-594-0318; e-mail
ehare@arrl.org. Additional information is available at arrl.org
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