The problems you are experiencing may be caused by vehicle noise.   Use this document to identify and reduce vehicle noise. It may not be possible to completely eliminate all vehicle noise.

 

Noise on a mobile CB is caused by one of 2 things:

 

1. Engine noise

2. Atmospheric (background) noise

 

The more noise there is, the shorter the range.   This is because you will need a stronger signal to hear it above the noise.

 

First identify what kind of noise it is:

 

  1. Listen to the noise with the engine running and with the engine stopped.
  2. If there is more noise with the engine running, then the noise is coming from the vehicle (engine noise).
  3. If the noise is the same, then it is atmospheric noise.  Atmospheric noise will be high during the day and significantly less at night (at least 2 hours after sunset, or an hour before sunrise).

 

What To Do

 

  1. If the noise is coming from the vehicle, then it can be reduced or eliminated.  Refer to the instructions later in this text.
  2. If it is atmospheric noise, then there is not much you can do:
  1. If your radio has an RF Gain control, then try turning it down a bit to eliminate some of the noise.  Turning down the RF Gain will reduce receiver sensitivity (and thus receive range), so don’t turn it down too much.
  2. To maximum your range, use the longest antenna possible and get the SWR as low as possible.
  3. Sorry, that’s it.  It is not possible to filter atmospheric noise.  There are no filters you can buy which will help.  

 

 

Atmospheric Noise

 

Believe it or not, but SUNSPOTS affect the background noise.  Sunspots are dark areas on the surface of the sun, a kind of "storm" on the sun.   They are dark because they are cooler than the surrounding area.

 

Sometimes there are a lot of sunspots, and sometimes there are hardly any.  The number of sunspots follows an 11 year cycle.  The level of sunspot activity actually has an effect on radio communications on the earth.  This happens because the sunspot activity has an effect on the ionosphere.  The ionosphere is an electrically charged layer at the top of our atmosphere, and it is important for radio communications.   Changes to the ionosphere will affect radio communications.  

 

It's all kind of complicated, but here's all you need to remember:

  1. A low number of sunspots is good for CB communications.
  2. A lot of sunspots is bad for CB communications.
  3. Sunspot activity follows an 11-year cycle.  So the background noise 11 years ago was as bad as it is today.  Do you remember?

 

We are currently in a period of increased sunspot activity, which makes more background noise.  Sometimes the noise is terrible, and the needle on the CB rides really high.  At night, when the sun is gone, the noise is significantly less.  Expect sunspot activity to be high throughout 2001 and 2002, and slowly tapering off in 2003 through 2005.  

 

Since channel 19 is the most popular channel, it will also be the noisiest.  All those people transmitting on channel 19 will add to the background noise.  Other channels should be quieter.

 

 

ELIMINATING ENGINE NOISE 

 

An automotive environment contains numerous sources for electrical noise:

 

  • Alternator noise
  • Ignition noise (high voltage to fire the spark plugs)
  • Fan motor (blower motor)
  • Electric fan on radiator
  • Windshield wiper motor
  • Electric Fuel Pump
  • On-board computer (all newer cars have one)

 

Disconnect the antenna from the CB and see if you still hear the noise.  

 

  • If the noise stops, then the noise is entering through the antenna system.
  • If you still hear the noise, then the noise is entering through the power wires.

 

 

NOISE ENTERING THROUGH ANTENNA SYSTEM

 

  1. Check the antenna SWR on channels 1 and 40.   The SWR must be below 3, and below 2 is ideal.  The lower the SWR, the better the performance.  
  2. Ground the chassis of the radio by connecting a wire from a ground screw under the dash to a screw on the side of the radio.
  3. The antenna cable may be picking up noise.   Try re-routing the antenna cable.
  4. Try relocating the antenna to a different part of the vehicle (if possible).
  5. If the noise persists, it will be necessary to identify the source of the noise and filter it at the source.

 

 

 

NOISE ENTERING THROUGH POWER LEADS

 

  1. Ground the chassis of the radio by connecting a wire from a ground screw under the dash to a screw on the side of the radio.
  2. Try another source of power.  The cleanest source of power is directly from the battery.   If you connect directly to the battery, shielded cable is recommended to prevent noise pickup from the ignition system.   It is also recommended to use a 3 amp fuse right at the battery if you connect directly to the battery.
  3. Try installing a noise filter on the power leads, as close as possible to the radio.  Radio Shack sells a variety of automotive noise filters.