Narrowband Basics

For the Wildland Firefighter Community

November 11, 2005

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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.

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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.

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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.

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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.

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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 frequency’s bell.

• Wideband – uses a range 25kHz wide.• Narrowband – uses a range 12.5kHz wide.

(half the wideband bandwidth)

• Deviation– The amount of modulation (voice) carried

on a frequency within its assigned bandwidth. • Wideband deviation is 3-5kHz.• Narrowband deviation is 1.5-2.5kHz.

(half the wideband deviation)

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Wideband vs. Narrowband

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Why New Radio Equipment?

• Narrowbanding halved a frequency’s 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 radio’s 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 radio’s 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.).

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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.

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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 radio’s received audio will become very loud.

– Audio may not be picked up (processed) by wideband receiver.

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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.

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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.

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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.

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Tones

• Tones are not required on receive (Rx). • Tones keep a radio’s 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.

“When thinking of tones, think of a bank’s 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.”

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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.

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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.