Nortek Security and Control KB

Remotes have poor range

Radio Interference (RFI)

Possible RFI Sources:

Linear wireless systems work on radio Frequency (RF) and are subject to outside Radio Frequency Interference (RFI). This interference can come from many sources and may cause reduced range or non-operation, depending on the strength of the RFI.

All Linear Access and Security products must meet FCC Part 15 requirements:

All Linear radios are required to comply with FCC Rules and Regulations as Part 15 devices. As such, they have limited transmitter power and therefore limited range.

A receiver cannot respond to more than one transmitted signal at a time and may be blocked by radio signals that occur on or near their operating frequencies, regardless of code settings.

All radio links should be tested regularly to protect against undetected interference or fault.

Radios that have worked for years may stop working because of a new RFI source

Some examples of RFI sources:
  • Nearby airports, television or radio transmission towers, military installations, power lines, and cell phone towers, along with many other sources, can cause RFI.
  • Appliances within 10’ - 15’ of the receiver, whether they’re running or not. If they are plugged in, they are a potential source of interference.
  • Plug-in transformers including the types used to charge cordless appliances, razors, laptop computers, power tools, tablets, etc.
  • Wireless doorbells
  • Wireless baby monitors
  • Computers
  • Game consoles
  • Wireless networks / Wi-Fi
  • Fax machines
  • Copiers
  • Cordless Phones
  • Sprinkler timers
  • Yard light timers
  • Christmas tree lights
  • Air conditioning or heating system thermostats
  • Florescent lighting fixtures
  • Halogen lighting fixtures
In order to find out if the RFI is coming from within the house, you should unplug appliances (washer, dryer, refrigerator, freezer, etc.), located within 15’ of the receiver, one at a time while trying the remote in question. If your range suddenly increases when you unplug a certain appliance, you’ve found the culprit! This doesn’t mean the appliance is defective, or dangerous, it simply means that it is the source of the radio interference. Since relocating an appliance is usually out of the question, you could try changing the location of the receiver. This can also make a difference in cases where you’re having a problem with radio interference (RFI) that has no identifiable source and nothing else works.

Linear makes a Radio Frequency Field Tester, the FT-1 (LDR00001) that will detect radio interference in the area around 318 MHz. It will decode any Megacode formatted RF data transmission and then give a beeping tone from the loudspeaker. Ambient RF noise or possible interference can be monitored.

A steady hissing noise is normally heard. This is the background noise of the radio. Any steady pulsing, low frequency buzzing or even voice traffic indicates an interfering signal that may reduce the maximum range of the system.

Interference Filters:

While it is beyond the scope of this article to provide a comprehensive list of Radio Frequency Interference (RFI) sources, the following are some examples and possible solutions.

NOTE: Radio Shack components are used only as examples and some of the numbers may be obsolete. Other sources of RFI filters are available (Search for "RFI Filters” on the Internet).

Signal and control lines can conduct RF emissions and conduct RF energy from an offending source to the receiver. Radio Shack sells a series of snap on ferrite filters (P/Ns 273-104 and 273-105). These often will clean up the signal if placed close to the source of the interference or at the receiver terminal strip. If possible, wrap several turns around the ferrite core before snapping the core shut.

Power line EMI filters / surge suppressors (P/N 61-2333) will reduce power supply noise from computers and other noise generators. Although it is less effective to place filters at the receiver, this may still help if the source of the interference is not known.

Telephone lines can also conduct RF signals and interfere with radio receiver range. A Radio Shack, telephone RF Line Noise Filter P/N 43-150 may help to clean up the noise. This would be most noticeable when using a telephone entry system as the telephone line is routed into the housing, in close proximity to the built in receiver.

Antenna leads may become corroded and dirty. They should be cleaned to be sure that they are making good connections. Poor antenna connections will cause the RF signal level to be reduced or the signals to be noisy.

For an isolated low voltage AC transformer, the clamp on ferrite cores may be effective but wrap several turns around the ferrite material (P/Ns 273-104 and 273-105) before closing the clamp. Place the ferrite core as close to the power input terminal strip as possible.

If DC power (usually 12 volts) is being used, Radio Shack has a series of filters that are normally used for automobile radios and stereos. The power supply should, normally, be as close to the to the receiver as possible. For short runs of wiring first try plugging the DC power supply into an AC power line filter. If that is not effective, try using the following noise filters: (P/Ns 270-030 (3 Amp), 270-051 (10 Amp), or 270-055 (20 Amp), depending on availability and required current ratings. In extreme cases, it may be necessary to use an AC power line filter as well as the above listed noise filters.

The following link will open a technical bulletin presented by the Door & Access Systems Manufacturers Association. The bulletin discusses possible sources of interference:


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