Narrowband Basics

1
Narrowband Basics
November 11, 2005

• For the Wildland Firefighter Community

2
Objectives

• Understand the why, what, and when for
  narrowbanding.
• Review some radio communication basics.
• Understand the differences between wideband and
  narrowband.
• Develop an awareness of potential problems.

3
Why the Switch to Narrowband?

• Increase the number of available frequencies for
  general use.
• Many federal agencies, including wildland fire
  agencies, use radio frequencies between162MHz
  and 174MHz.
• Where there was one frequency now there are two.
• Increasing the number of usable frequencies
  reduces frequency congestion.

4
What Has Changed?

• The National Telecommunications Information
  Administration (NTIA) refarmed frequencies used
  by government agencies.
• As a part of refarming, each 25kHz wideband
  channel was divided into two 12.5kHz narrowband
  channels.
• There are now twice the number of available
  frequencies.

5
When Did the Change Occur?

• In 1995, Congress mandated that all federal
  agencies transition to narrowband frequencies by
  January 1, 2005.
• In the future narrowbanding will continue to be
  the standard
• In 2013, the FCC will require all stations to be
  narrowband.
• When technology permits, each 12.5kHz frequency
  will again be divided in half, resulting in an
  even narrower frequency of 6.25kHz.

6
A Channel is Defined By Its..

• Frequency
• Every channel on a radio has a specific
  frequency.
• FM frequencies are shaped like a bell.
• The bell seen on a spectrum analyzer and
  indicates the signal strength as a function of
  frequency.
• Bandwidth
• The width of a frequencys bell.
• Wideband uses a range 25kHz wide.
• Narrowband uses a range 12.5kHz wide.(half the
  wideband bandwidth)
• Deviation
• The amount of modulation (voice) carriedon a
  frequency within its assigned bandwidth.
• Wideband deviation is 3-5kHz.
• Narrowband deviation is 1.5-2.5kHz. (half the
  wideband deviation)

7
Wideband vs. Narrowband
8
Why New Radio Equipment?

• Narrowbanding halved a frequencys bandwidth and
  deviation.
• Many older wideband radios could not operate on
  frequencies set 12.5kHz apart. They could only
  be set to frequencies 25kHz apart.
• An older wideband radios bandwidth is 25kHz
  wide. This would interfere with both new 12.5kHz
  narrowband frequencies on either side of the old
  25kHz frequency.
• An older wideband radios deviation is 5kHz. New
  narrowband radios would see this high deviation
  level and would either
• Not process the wideband deviation into a
  received audio signal.
• Process it into a bad received audio signal
  (garbled, distorted, etc.).

9
Interference

• Interference occurs when both wideband and
  narrowband are used to communicate on the same
  channel.
• This is the cause of many of our current
  communication problems.
• Channels are programmed for either wide or
  narrowband.
• Channels must be programmed consistently for all
  radios in use.
• Not all cooperators and Federal agencies are
  narrowband capable.
• Includes ancillary equipment, such as repeaters,
  handhelds, and mobiles.
• Units broadcasting wideband need to be
  reprogrammed to narrowband and given a warning,
  or if the radio is wideband only, they need to be
  sent home or issued a cache radio.

10
Possible Interference Problems

• Narrowband Communication on a Wideband Channel
• Received audio may be very soft and quiet.
• Caution, wideband radios must turn up volume to
  hear. However, once a second wideband radio
  transmits, the original wideband radios received
  audio will become very loud.
• Audio may not be picked up (processed) by
  wideband receiver.

11
Possible Interference Problems

• Wideband Communication on a Narrowband Channel
• Received audio may be loud, distorted, or
  inaudible.
• Communications may work at a distance but no
  audio may be received when close to receiver.
• Usually the cause of mixed band communication
  problems.
• Caution, if you turn down the volume, narrowband
  communications may not be heard.

12
Programming Tips

• To change the bandwidth for your radio, you must
  program it for either narrowband or wideband,
  plus enter the correct frequency.
• Entering the frequency with just 3 decimal places
  does not set your radio to wideband.
• The deviation is automatically changed when you
  program the bandwidth.
• The agency communications technician should know
  which frequencies are wideband and which are
  narrowband, although this may not always be the
  case.
• Most federal communication systems use
  narrowband.
• Commercial and local government communication
  systems may be wideband or narrowband, though
  most are wideband.

13
Repeaters

• Repeaters use a pair of frequencies, one for
  transmitting (Tx) and one for receiving (Rx).
  Either Tx or Rx may have a tone.
• Forest and districts typically use the same
  repeater pair at several repeater sites.
• The only way to chose which repeater to talk to
  is by using the correct tone.
• Tones are used to keep the repeater from
  responding to unwanted noise and unwanted
  communications on the same frequency.
• Repeaters used in a mixed band environment may
  shutdown, then reset, thereby stopping all
  transmission for up to three minutes or the
  duration of the offending call.

14
Tones
When thinking of tones, think of a banks safety
deposit box. You need two keys to open it. One
key is the frequency and the key second is the
tone. Unless you have both, nothing happens.

• Tones are not required on receive (Rx).
• Tones keep a radios receiver from responding to
  unwanted noise.
• Your radios use analog tones (CTCSS, DPL, PL, CG,
  and QT).
• There are 43 standard EIA/TIA tones different
  analog tones (110.9, 123.0, etc.). Only a few
  tones are used by wildfire agencies.
• Tones can be programmed into any radio (portable,
  mobile, base, or repeater).
• A receiver set to operate with a specific tone
  will not turn on if the correct tone is not
  sent by a transmitter.
• When a tone is not required by a receiver, it
  does not matter whether a transmitter uses a tone
  or not.

15
Avoiding Problems

1. Do not operate in a mixed band environment. Only
   use narrowband.
2. Issue narrowband capable equipment to those with
   wideband only equipment. Report the deficiency
   back to dispatch and their home unit.
3. Establish reliable communications before entering
   the field.

16
Programming Help

• The http//radios.nifc.gov/ site has up-to-date
  tips, news, and troubleshooting information.
• Check this site to find the following
  information
• How to verify if radio is narrowband or wideband.
• How to program your radio for narrowband or
  wideband operation.