 |
 |
|
|
|
|
|
|
||||||||||||||||
|
|
|||||||||||||||||
|
|
|||||||||||||||||
|
|||||
|
|
Compiled by: Ed Hare, W1RFI, ARRL Lab Supervisor, w1rfi@arrl.org
Update: April 8, 1999
Copyright © 1998, 1999 by The American Radio Relay League, Inc. All rights reserved.
Prepared as a membership service by the American Radio Relay League, Inc., Technical Information Service.
For your convenience, you may reproduce this information, electronically or on paper, and distribute it to anyone who needs it, provided that you reproduce it in its entirety and do so free of charge. Please note that you must reproduce the information as it appears in the original, including the League's copyright notice.
If you have any questions concerning the reproduction or distribution of this material, please contact The ARRL Technical Information Service Coordinator, American Radio Relay League, 225 Main St., Newington, CT 06111 (email: tis@arrl.org).
Overview
About Wireless Jacks
ARRL Testing
Manufacturer and Cable Company Responses
How to Fix the Problem
More Information
Listen to a Reading of Wireless Modem Jack Interference
Background on Part 15 of the Applicable FCC Regulations
The ARRL has received reports of local interference from noisy and somewhat "drifty" carriers near 3.520 MHz. They can range anywhere from 3.510 to 3.550 MHz. Most of the initial reports were initiated on the Northern California Contest Club reflector and forwarded to ARRL HQ by Brad Wyatt, K6WR, the ARRL Pacific Division Director. Harmonics of these signals have also been reported as high as 20 meters. An informal investigation in the Greater Hartford, Connecticut, area revealed several local, nonamateur signals, including some carrying FM voice transmissions that appeared to be telephone conversations. One signal heard in a residential neighborhood literally pinned the S meter at 60 dB over S9. These reports include interference ranging from S7 to 60 dB over S9. By any standard, the S7+ carriers monitored on popular ham frequencies constitute harmful interference.
The interference is being caused by wireless modem jacks, commonly installed with the digital cable converter for digital cable television. They use the electrical wiring to make a convenient connection from the cable box to the telephone line to transmit billing information. These devices are also being sold in some computer retail stores. They are first cousins to "wireless telephone jacks," also being marketed in retail stores.
These tests and reports from the field demonstrate that the wireless modem jacks pose a serious problem for reception on the lower part of the 80-meter amateur band and possibly on other bands because of harmonics. Likewise, the devices also are very susceptible to interference from HF signals. The ARRL Lab has received many reports of interference from these devices.
At this time, wireless jacks are being manufactured by the Phonex Corporation, 6952 High Tech Drive, Midvale, Utah 84047, (801) 566-0100, http://www.phonex.com/.
Wireless jacks are "carrier-current" devices, meaning that they conduct their RF signals over the power lines. They are full-duplex transceivers that use the ac electrical system to connect a remote telephone to the phone system, using FM signals conducted by the electrical wiring.
There are two types of jacks, very similar in design and function that are being made by Phonex and marketed under several brand names - wireless modem jacks and wireless telephone jacks. Early version of wireless modem jacks use 3.52 and 8.27 MHz for their full-duplex operation. These are the ones causing the interference problems on some HF amateur bands. They are also very susceptible to interference from HF transmitters, especially those that operate on the 80-meter amateur band.
The wireless telephone jacks, marketed under GE, RCA/Thompson and Radio Shack brand names, operate on 3.025 and 6.436 MHz. They are not likely to cause any interference problems, although they are also susceptible to interference.
In early version of the wireless modem jacks, the 3.52 MHz carrier is on all of the time, even when the phone lines are not in use. The 8.27 MHz signal appears only when the modem is in actual use. The 3.52 MHz signal is generally modulated only when the modem is in use. Analog phone signals from other phones in the house usually do not appear on the transmitter carrier, although the ARRL has received reports of telephone conversations near 3.52 MHz.
The modulation is narrow-band FM (NBFM) with a maximum deviation of +10KHZ and -25KHz (not symmetrical for very loud audio). The transmitter output impedance is approximately 15 ohms. The open circuit voltage is approximately 2.4 Volts RMS across the line and the short circuit current is approximately .15 amps. This would result in a maximum power of approximately 100 milliwatts into a matched load.
Under some circumstances, the unit gets into a mode where it produces a broad band interference that falls off at about 10 dB every 5KHz on either side of the signal. This is different than "normal" where it produces a T8 or T7 unmodulated note.
They are permitted, within certain limits, by FCC Part 15 rules on most frequencies, even on the ham bands. However, the rules state the operators of Part 15 devices must ensure that they do not cause interference to other radio services.
There is an "FCC ID" number on wireless jacks. This is a Part 68 registration number, indicating the unit meets the appropriate standards to be used on a telephone system.
The 3.52-MHz units carry a registration number similar to HMTCHN-24794-KX-E and are sold as under various model numbers under several brand names. They are also used by TCI cable in conjunction with their digital cable systems.
The 3.025-MHz units carry and ID number similar to AAOIND-25424-RJ-N and are also sold under various model numbers under several brand names, including RXC/Thompson, GE and Radio Shack.
According to the FCC registration number, the device is manufactured overseas by PT LINTAS ELEKTRONIKA DINAMIKA INDAH. It was registered with the FCC on 4/14/98.
The wireless modems all operate on 3.52 MHz and 8.27 MHz and are being sold to TCI cable and are being marketed to several computer-stores and other distributors under several brand names. According to Phonex, there have been relatively few digital modems marketed in retail stores. The wireless telephone jacks operate on 3.025 and 6.4 MHz and are being marketed under RCA, GE and Radio Shack brand names.
The ARRL Lab has obtained a TCI unit and one of the retail wireless modem jacks. As expected from information we received from Phonex, these units all operate on 3.52 MHz. (Again, the wireless telephone jacks operate on non-amateur frequencies.) The Lab verified the extent of the problem; these devices result in serious interference to the lower part of the 80-meter amateur band. From tests done in the ARRL Lab, we've determined that these devices also are very susceptible to interference from 80-meter signals (and perhaps other bands).
Ed Hare installed one in W1INF, the ARRL HQ operators club station. It is located on the ground floor, appropriately right near the Lab. The antenna is on the HQ-building roof, about 3 stories up. In this configuration, he found an S9 + 10dB signal, about 50 dB higher than the digital noise from all the HQ staff computers and local-area networks. When W1INF was placed on the air with 1500 watts, or W1AW bulletins came on, the devices suffered total blanking. At 100 watts, the interference consisted of very strong and objectionable key clicks.
Dave Sumner, K1ZZ, ARRL's Executive Vice President purchased one of the wireless modem jacks at a local computer store. It operated on 3.538 MHz and gave an S9+20 signal on receive antennas located about 100 feet from Dave's house. It was also easily susceptible to about 50 W on the low end of the 80-meter band.
ARRL HQ also did some informal "field testing" as well. ARRL staffer Rick Lindquist, N1RL, checked out the situation in several neighboring towns served by TCI Cable with his HF mobile station tuned to the low end of 80. In those towns, Rick reports that every several blocks he heard a carrier--sometimes multiple carriers--in the vicinity of 3.52 or 3.53 MHz. At one location, he reported a signal that pinned his S meter at S9 + 60 dB! ARRL Lab Supervisor Ed Hare, W1RFI, reports that using a 15-foot wire antenna at his QTH, he heard a signal at about S9 +10 dB. One evening, he heard actual telephone conversations on this frequency.
These devices would be problem enough if they met FCC Part 15. A "legal" signal at 30 uV/m 30 meters from the source would result in a S9+15 dB signal under some circumstances. (Amateur Radio would still be protected by the "non-interference" provisions of Part 15.) However, the ARRL Lab has received a report done of tests done in the field by a Professional Engineer that indicate that some of these devices are producing some very strong signals, apparently over the permitted limits.
These field reports include interference ranging from S7 to 60 dB over S9.
To gather more information about these products, the ARRL Lab has been in communication with a number of its professional contacts. Ed Hare first contacted one of his contacts on the Board of Directors of the Society of Cable Telecommunications Engineers. He introduced Ed to Tony Werner, the Senior Engineer of TCI cable. Ed also called Phonex and discussed the problem with Scott Bullock, KK7LC.
Both companies were extremely cooperative in resolving the problem, however. Ed Hare summed it all up pretty nicely. "When I started receiving the reports that indicated that this is a widespread problem, I knew ARRL had to act quickly," he said.
Part 15 requires that these devices be tested by the manufacturer (Verified) before they are marketed. According to a spokesman from Phonex, "All Phonex wireless products are tested to meet applicable FCC Part 15 regulations. Verification of compliance is performed by an independent test facility certified by the FCC to perform Class B certification testing. Site test performed for verification to FCC Part 15 Sec. 209 are performed in adherence to ANSI standards under the direction of the Phonex Corporation Engineering Department. 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."
The good news from all this is that Phonex has responded appropriately. Within days of receiving the first reports from hams, Phonex has moved the frequency of their units being manufactured from 3.5 MHz to 3.3 MHz and has made engineering changes to prevent the units from transmitting a dead carrier when the unit is not in actual use. They also said that 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. They have been working with TCI to implement this and have sent letters to their distributors, explaining the problem and Phonex's solution.
TCI's Executive Vice President of Engineering and Technical Operations, 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. 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. They will also routinely replace 3.52 MHz units as part of their customer-service programs.
TCI can be contacted through their local customer-service centers.
Immediately after TCI and Phonex were contacted by the ARRL regarding the report that the Wireless Modem Jack may cause local interference with some HF transmitters operating at the 3.53 Mhz frequency, action was taken to address this problem. An update of progress is listed below:
TCI and Phonex continue to offer voluntary cooperation with the ARRL and the Amateur Radio community to address complaints of interference. There is also a plan in place to continue to replace the original 3.53 MHz modem jack even in cases where there is not a complaint of interference.
Given the scope of this assignment, TCI and Phonex ask for the patience of the amateur radio community as efforts to begin implementation of the solution are underway. The voluntary cooperation of TCI, Phonex and ARRL has been an important part of the ability of all three organizations to focus resources on the issues.
Amateur radio users that are active on the 80 meter band are welcome to contact Phonex with any questions. Please feel free to email inquiries to sbullock@phonex.com to reach Scott R. Bullock (KK7LC) the Phonex VP of Engineering. You may also call the Phonex toll free number at 1 (800) 437-0101; fax inquiries can be sent to Phonex at 1 (801) 566-0880.
Most of the wireless modem jacks have been sold to TCI cable for use with the control unit for their digital cable installations. A much smaller number have been sold in computer stores as wireless modem jacks. Wireless modem jacks, or wireless telephone jacks, may also have been used by some installers of DSS satellite systems.
The majority of these devices are operated by TCI, however, so hams who live in an area where TCI has installed digital cable should contact their local TCI office as a first step. As of January 18, ARRL has received reports that some TCI field offices are dealing effectively with problems. Other offices, however, appear to be a bit slower in coming up to speed. TCI has nearly a thousand field offices, all of which have to get the word, and these types of communications problems are inevitable. Bill Scheffler, Vice President of Technical Operations for TCI, offered a suggestion on how to best approach the local offices. "Any Hams calling a Local TCI office with interference in the 3.53 MHz range that is suspected to be coming from one of the Phonex Wireless Phone Jacks needs to refer to the Phonex product and the fact that this equipment has been installed (albeit in low numbers) in most TCI systems that supply Digital services. If the TCI Cable System doesn't carry the Digital product there would be no reason for the cable system to install these devices and the Ham operator will need to look else where for the offending source of these signals."
Scheffler has generated an email memo from TCI corporate to their regional engineering staff, directing that they help hams resolve this on a priority basis. The ARRL has obtained TCI's permission to reproduce that memo here. This memo states:
>-----Original Message----- > From:Scheffler, Bill > Sent:Friday, January 15, 1999 2:49 PM > To: Degenhardt, Jim; Harlin, Mike; Harrigan, Mark; Hershey, Earl; > Murphy, Dan; Page, Jeff > Cc: Werner, Tony; Smith, Lauri > Subject: Phonex Wireless Phone Jacks > Importance: High > > This communication is to enlist your assistance in tackling a > problem that needs immediate attention and to advise you that > we will be contacting all of the Cable Systems in your Division > with Digital customers to address the issue described below. > > Some of the Digital installs that have been done required the use > of a wireless phone jack. > > The Phonex wireless phone jacks that are in use today have the > potential to interfere with certain amateur radio users. Even > though the device complies with FCC part 15, they can still > cause interference. Under part 15, we as the operator need to > suspend operation of these devices if they are causing > interference. The ARRL, (an organization associated with Ham > radio operators) will be releasing an article this week. The > HAM operators have a tremendous network of users and as good > corporate citizens it is extremely important that we work > toward insuring that our cable operations do not interfere > with the spectrum they are licensed to use. > > The approach that we need to take is as follows: > > 1.0 Phonex is immediately changing the frequency on all new > devices from 3.53 MHz to 3.3 MHz. This new frequency will not >interfere with the HAM operators. > > 2.0 It is extremely important that if we get complaints from > HAM operators that we get the call routed over to someone > knowledgeable so that we can find the location of the > interfering device and get it removed from the system. > > 3.0 We need to start a program to migrate the 3.53 MHz devices > out of the systems and replace them with either the 3.3 MHz > devices or a copper extension. I would suggest that we do this > via churn and if we are running a service call in a home with > one of the offending devices, (even on an unrelated issue) > that it be changed out during that visit. > > 4.0 The new devices that operate at 3.3 MHz are identifiable > by a bar code on the back. The 3.53 MHz devices do not have > a bar code. >
Note from Ed Hare/ARRL: This latter point has proven to be in error. The 3.52 MHz devices do have a bar code. The 3.3 MHz units are expected to be in most TCI offices on or around 2/15/99. -- Ed Hare.
> 5.0 Chuck Schultz will be working with Phonex on the logistics > of getting the recycled devices retuned. > > Expect a spike in activity over the next period of time as the > Following article goes out to most HAMs.
Hams who have problems with their local TCI offices should first try to resolve the problem locally. A bit of polite persistence, or perhaps asking to be transferred to a supervisor should help resolve any misunderstandings with customer-service personnel. (In such a large undertaking, such things are inevitable.) Hams can also print information from this Web page, especially the TCI memo, to help the local offices better understand the problem. Ed Hare has agreed to act as a liaison between the amateur community and TCI at the corporate level. If a ham has a problem that he or she is not able to resolve with the local office, they should contact Ed Hare. Ed will either help the ham with information, advice or forward the contact immediately to TCI corporate, who will help the local office better understand how to correct this problem.
Ed says, "TCI and Phonex have been very cooperative throughout this process, but they asked if ARRL would be willing to help channel problems to them as appropriate. I have volunteered ARRL to help resolve any problems that might crop up, ranging from helping hams to understand the issue to explaining to TCI and some newcomers that not every tuneup signal on 3.53 MHz is a wireless modem jack to helping hams resolve any problems they may encounter with local TCI offices by forwarding a summary of those problems to the corporate engineering staff at TCI.
"While TCI expects that they will become involved with a few problems that are not actually caused by TCI equipment, we are trying to minimize the impact of this on them by being careful that they are not asked to do things that are not under their control, such as to correct a problem on another nearby frequency that is not related to wireless modem jacks or to correct a problem from a non-TCI installation, such as a DSS satellite system or a neighbor using a wireless modem jack with a computer system.
"I have taken this approach so we, too, can demonstrate the good faith that Phonex and TCI have shown by first trying to work with the information published by ARRL and within the processes that Phonex and TCI have set up. It could be months before the lion's share of this is identified by hams and corrected by TCI and Phonex. I am in this for the long haul, though; we have a good chance at a success story that we can build into similar good relationships with other cable companies and Part-15-device manufacturers. Those who say Dave Sumner's Feb QST editorial will probably get the idea that ARRL is in this for the long haul, too, and is looking for big picture solutions to the general noise problems that are eating away at our bands. This one may serve as an important stepping stone in that direction.
"Hams can contact me with questions or help in resolving problems. I would also like to receive all reports of interference from any type of Part 15 device. I am considering how we can best approach the FCC and want to have as much information available about the impact of Part 15 devices on the Amateur Radio Service."
Ed Hare summarized this by saying, "This is still progressing reasonably well in most areas. While we would all like to see this problem corrected overnight, there was a lot that had to happen, and still needs to happen, to get that happy ending that we all hope to see. This problem is rather large -- covering the US from coast to coast and all involved parties are making progress that is much faster than I usually see these things go. Phonex and TCI have been forthright and responsive from day one. In their memo, TCI was pretty clear -- TCI expects that they need to fix the problem and are taking steps to ensure that their service organizations are well informed about the problem and the solutions.
There has been a bit of confusion among hams and some of the TCI staff about these modems. In general, these devices are permitted under Part 15 regulations, subject to certain limits. These limits, however, can create some pretty strong signals in the ham bands! Part 15 also has a requirement that Part 15 devices not cause harmful interference to radio services. It was on that basis that ARRL, Phonex and TCI addressed correcting the problem.
TCI has agreed to correct all cases of harmful interference as quickly as possible. Although not required by Part 15, they have also instituted a policy whereby these devices will be removed from service as part of their normal maintenance procedures. Both actions show good faith. But Amateur Radio needs to show good faith, too. We need to ask TCI to correct those problems that are actually causing interference, but we should not go looking for trouble. If a 3.53 MHz device is not causing actual interference, Part 15 does not require that the operator of the device take any corrective action. Hams should not be driving mobile equipment all over town to identify all the "leaks;" there will be plenty of signals heard, even strong ones, but they are legal under Part 15. Let's make sure that TCI resources are put where they need to be right now -- correcting the serious interference that some hams are actually experiencing.
What constitutes harmful interference? Part 15 is rather vague:
In practical terms, "harmful interference" is in the eye of the beholder. In legal terms, it would mean whatever the FCC determined it meant, if they had to become involved. I think that few would argue that S9+ signals are harmful interference. The FCC would probably not find that a signal just audible above the ambient noise was harmful interference. They would probably not find that a signal that can be heard on an unused frequency in the 80-meter band is harmful interference. As a service, we probably don't want to put that to the test. Let's approach TCI as fairly as they have approached us and ask them to correct those devices that are causing us harm. Although that mobile trip might be helpful, to identify the S7 signal that turns out to be 0.75 miles away, hams should be careful in their dealings with local TCI staff that they differentiate clearly between a request to correct interference and a signal report designed to help track that interference to the source.
Ed Hare credits teamwork with resolving the wireless modem problem. Many hams were also involved, notably several member of the Northern California Contest Club, the hams of Phonex, 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.
"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. To me, this cooperation and teamwork 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.
He continued, however, "In most areas, TCI is making progress, although a bit slower than hams would like. In other areas of the country, the progress has been very slow, with no perceptible improvements. I have recently been in contact with TCI corporate engineering staff about the need to have 'voluntary cooperation' proceed at a reasonable pace. I encourage hams to keep me appraised of the progress TCI is making in their areas so that ARRL can judge how much additional encouragement needs be offered at the national or regulatory level."
An article on the subject appeared in the December 24, 1998 issue of the ARRL Letter. An article appeared in the March, 1999 QST "Happenings" column.
Amateurs with questions about this topic or those who encounter any problems getting their problems resolved with TCI or the manufacturer can contact Ed Hare, W1RFI, the ARRL Laboratory Supervisor, 225 Main St., Newington, CT 06111, tel: (860) 594-0318, email: w1rfi@arrl.org.
TCI can be contacted through their local customer-service centers.
This audio recording (RealAudio) was supplied to ARRL by Jim McCook, W6YA. In some crowded residential areas, there can be a lot of signals heard simultaneously. This is a recording made when Jim tuned from 3.505 to 3.550 MHz.
Wireless jacks are unlicensed devices that are permitted, with certain limitations, under Part 15 of the FCC rules, which defines them as "unintentional radiators." But because they use the ac wiring to conduct their signals, they must comply with the general limits for "intentional radiators" under Part 15. These limits permit unlicensed, radiated signals on HF of up to 30 uV/meter--even on the ham bands. But, these devices also are required by Part 15 to not interfere with licensed users of the spectrum.
They are carrier-current devices, meaning that they conduct RF over the power lines. As such, they are classified as "unintentional radiators and are subject to various Part 15 limits on conducted and radiated emissions. Under Part 15, such devices are "Verified," meaning that the manufacturer is required to test the units for compliance with all provisions of Part 15. The manufacturers are not required to submit their test results to the FCC, but must keep them on file. Once they have been tested and passed, they may be marketed.
Carrier-current devices have the specific requirement that they be tested in three "typical" installations.
The following definitions in Part 15 lay the groundwork for the ensuing discussions:
Section 15.3 Definitions.
(m) Harmful interference. Any emission, radiation or induction that endangers the functioning of a radio navigation service or of other safety services or seriously degrades, obstructs or repeatedly interrupts a radiocommunications service operating in accordance with this Chapter.
(o) Intentional radiator. A device that intentionally generates and emits radio frequency energy by radiation or induction.
(z) Unintentional radiator. A device that intentionally generates radio frequency energy for use within the device, or that sends radio frequency signals by conduction to associated equipment via connecting wiring, but which is not intended to emit RF energy by radiation or induction.
Part 15 is a morass of complex, interwoven regulations. Carrier-current devices are unintentional radiators. However, carrier-current devices that operate below 30 MHz are generally subject only to the requirements for radiated emissions. However, there are no specific limits for radiated emissions for unintentional radiators for frequencies below 30 MHz, so Part 15 stipulates that carrier-current devices that operate below 30 MHz are subject to the radiated emission limits for intentional radiators.
The permitted radiated levels are described in Part 15:
Section 15.109 Radiated emission limits.
(a) Except for Class A digital devices, the field strength of radiated emissions from unintentional radiators at a distance of 3 meters shall not exceed the following values:
| Frequency of Emission (MHz) | Field Strength (microvolts/meter) |
|---|---|
| 30 - 88 | 100 |
| 88 - 216 | 150 |
| 216 - 960 | 200 |
| Above 960 | 500 |
***
(e) Carrier current systems used as unintentional radiators or other unintentional radiators that are designed to conduct their radio frequency emissions via connecting wires or cables and that operate in the frequency range of 9 kHz to 30 MHz, including devices that deliver the radio frequency energy to transducers, such as ultrasonic devices not covered under Part 18 of this Chapter, shall comply with the radiated emission limits for intentional radiators provided in Section 15.209 for the frequency range of 9 kHz to 30 MHz. As an alternative, carrier current systems used as unintentional radiators and operating in the frequency range of 525 kHz to 1705 kHz may comply with the radiated emission limits provided in Section 15.221(a). At frequencies above 30 MHz, the limits in paragraph (a), (b) or (g) of this Section, as appropriate, continue to apply.
and
Section 15.209 Radiated emission limits, general requirements.
(a) Except as provided elsewhere in this Subpart, the emissions from an intentional radiator shall not exceed the field strength levels specified in the following table:
| Frequency (MHz) | Field Strength (microvolts/meter) | Measurement Distance (meters) |
|---|---|---|
| 0.009 - 0.490 | 2400/F(kHz) | 300 |
| 0.490 - 1.705 | 24000/F(kHz) | 30 |
| 1.705 - 30.0 | 30 | 30 |
| 30 - 88 | 100 ** | 3 |
| 88 - 216 | 150 ** | 3 |
| 216 - 960 | 200 ** | 3 |
| Above 960 | 500 | 3 |
and:
Section 15.31 Measurement standards.
(d) Field strength measurements shall be made, to the extent possible, on an open field site. Test sites other than open field sites may be employed if they are properly calibrated so that the measurement results correspond to what would be obtained from an open field site. In the case of equipment for which measurements can be performed only at the installation site, such as perimeter protection systems, carrier current systems, and systems employing a "leaky" coaxial cable as an antenna, measurements for verification or for obtaining a grant of equipment authorization shall be performed at a minimum of three installations that can be demonstrated to be representative of typical installation sites. (Emphasis added -- Ed.)
Intentional Radiator Limits
The radiated limits for Part 15 devices that can be operated legally on any frequency, including Amateur Radio frequencies, are actually fairly high. Assuming far field conditions, an isotropic antenna should pick up about -58 dBm from a 30 uV/m field, or about 15 dB over S9, assuming S9 to be 50 microvolts into 50 ohms (-73 dBm at the receiver input terminal).
In addition to these absolute maximum requirements, Part 15 also requires that devices operated under Part 15 must not cause interference to authorized radio services. If such interference does occur, Part 15 requires the operator of the Part 15 device to take whatever steps are necessary to reduce or eliminate the interference.
Section 15.5 General conditions of operation.
[b] Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.
[c]The operator of a radio frequency device shall be required to cease operating the device upon notification by a Commission representative that the device is causing harmful interference. Operation shall not resume until the condition causing the harmful interference has been corrected.
Note: Reprints are available from the Technical Department Secretary, ARRL, 225 Main Street, Newington, CT 06111. Article copies must be prepaid $3 for ARRL Members, $5 for non-members. You may order by telephone (860-594-0200) and pay by credit card. Reprints can only be sent by mail and cannot be sent by or attached to e-mail.
This information was prepared as a membership service by the American Radio Relay League, Inc., Technical Information Service, 225 Main St., Newington, CT 06111 (860) 594-0214. Email: tis@arrl.org (Internet). ARRL HQ is glad to provide this information on the Web free of charge as a service to League members and affiliated clubs.
For your convenience, you may reproduce this information, electronically or on paper, and distribute it to anyone who needs it, provided that you reproduce it in its entirety and do so free of charge.
If you have any questions concerning the reproduction or distribution of this material, please contact:
