Bandwidth & Interference

What is bandwidth?

Bandwidth is the amount of radio spectrum a signal occupies.

Why is bandwidth important? Hams have a limited amount of

bandwidth to use and we must avoid interfering with each other.

Different modes of operation utilize different bandwidths.

Example: CW- 20 Hz (Continuous Wave = Morse

Code) PSK 31- 31 Hz (digital) RTTY- 250 Hz (digital) SSB- 2-3 KHz (single sideband telephony) FM (N)-5 KHz (telephony) FM (W)- 15 KHz (telephony) SCTV- 2.5 MHz (Image) FSTV- 6 MHz (Image)

Bandwidth

SSB Signal 2 - 3 kHz wide

FM Signal 5 - 15 kHz wide

UHF Fast-Scan TV ~ 6 MHz

Example of limited space…

2 meter band = 144-48 MHz, or 4 MHz bandwidth

A n FM repeater requires an input & output frequency. Each signal is FM and occupies 15 KHz of space for a total of 30KHz/repeater.

You can fit 12 repeaters in the 4 MHz bandwidth allotted to ham radio. But the band plan does not allow repeaters over the entire 4 MHz bandwidth!

Bandplan- A general agreement of what modes will be used in certain portions of each band. Each band has a specific bandplan that helps us

avoid interfering with each other. And make the best use of the available spectrum. Generally the lower portion of the band is designated for CW & data, the upper portion for phone and image communications.

Example- 20 meter band = 14.000 to 14.350 MHz, or a 350 KHz bandwidth.

20 meter Bandplan= 14.000 – 14.150= CW & data 14.150 – 14.350= phone & image

ARRL 10 Meter Bandplan (28-29.7 MHz):28.000-28.070 CW28.070-28.150 RTTY28.150-28.190 CW28.200-28.300 Beacons28.300-29.300 Phone28.680 SSTV29.000-29.200 AM29.300-29.510 Satellite Downlinks29.520-29.590 Repeater Inputs29.600 FM Simplex29.610-29.700 Repeater Outputs

Two Common Types of Modulation

AM- amplitude- the amplitude of the signal varies up and down

FM- frequency- the amplitude stays the same but the frequency varies

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Amplitude Modulation

An unmodulated RFAn unmodulated RFcarrier requires narrowcarrier requires narrowBandwidthBandwidth

Modulation of the carrierModulation of the carriercreates sidebands. Thiscreates sidebands. Thisrequires more bandwidth.requires more bandwidth.Transmitter power is Transmitter power is spread across this spread across this bandwidthbandwidth

(on and off is (on and off is CW)CW)

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AM and SSB

The carrier contains noThe carrier contains noaudio information.audio information.

The sidebands containThe sidebands containduplicate audio duplicate audio informationinformation

By filtering out the carrier and one sideband, we By filtering out the carrier and one sideband, we save spectrum and concentrate our RF energy save spectrum and concentrate our RF energy into a narrower bandwidth. SSB is therefore into a narrower bandwidth. SSB is therefore more efficient.more efficient.

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INTERFEENCE

Recognition and correction of problems A logical first step when attempting to

cure a radio frequency interference problem in a nearby telephone is to install an RF filter at the telephone.

The most likely cause of telephone interference from a nearby transmitter is the transmitter's signals are causing the telephone to act like a radio receiver.The following may be useful in correcting a radio frequency interference problem:

Snap-on ferrite chokes Low-pass and high-pass filters Notch and band-pass filters

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Recognition and correction of

problems If someone tells you that your transmissions

are interfering with their TV reception: First make sure that your station is operating

properly and; That it does not cause interference to your own

television.

When a neighbor reports that your radio signals are interfering with something in his home: The proper course of action to take is to check

your station and make sure it meets the standards of good amateur practice.

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Recognition and correction of problems

The most likely cause of telephone interference from a nearby transmitter is the transmitter's signals are causing the telephone to act like a radio receiver.

If someone tells you that your transmissions are interfering with their TV reception you should first make sure that your station is operating properly and that it does not cause interference to your own television.

The following may be useful in correcting a radio frequency interference problem: (you’ve seen these before) Snap-on ferrite chokes Low-pass and high-pass filters Notch and band-pass filtersAll of these answers are correct

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Recognition and correction of

problems (cont)

If a "Part 15" device in your neighbor’s home is causing harmful interference…..

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Recognition and correction of problems

When a neighbor reports that your radio signals are interfering with something in his home the proper course of action to take is to check your station and make sure it meets the standards of good amateur practice.

A logical first step when attempting to cure a radio frequency interference problem in a nearby telephone is to install an RF filter at the telephone.

If a "Part 15" device in your neighbor’s home is causing harmful interference to your amateur station you should: Work with your neighbor to identify the offending

device Politely inform your neighbor about the rules that

require him to stop using the device if it causes interference

Check your station and make sure it meets the standards of good amateur practice

All of these answers are correct

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Fundamental overload Symptoms of overload and overdrive

A fundamental overload, in reference to a receiver, is interference caused by very strong signals from a nearby source.

Receiver front-end overload is the result of interference caused by strong signals from a nearby source.

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Distortion

If you receive a report that your signal through the repeater is distorted or weak, the problem may be any of the following: Your transmitter may be slightly off

frequency Your batteries may be running low You could be in a bad location

Bandwidth and Interference Questions

19

Which emission type has the narrowest bandwidth?

A. FM voiceB. SSB voiceC. CWD. Slow-scan TV

20

Which emission type has the narrowest bandwidth?

C. CW

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What are phone transmissions?

A. The use of telephones to set up an amateur radio contact

B. A phone patch between amateur radio and the telephone system

C. Voice transmissions by radioD. Placing the telephone handset

near a radio transceiver's microphone and speaker to relay a telephone call

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What are phone transmissions?

C. Voice transmissions by radio

23

Which type of modulation is most commonly used for VHF and UHF

voice repeaters?

A. AMB. SSBC. PSKD. FM

24

Which type of modulation is most commonly used for VHF and UHF

voice repeaters?

D. FM

25

What is the approximate bandwidth

of a frequency-modulated voice signal?

A. Less than 500 Hz B. About 150 kHzC. Between 5 and 15 kHzD. More than 30 kHz

26

What is the approximate bandwidth

of a frequency-modulated voice signal?

C. Between 5 and 15 kHz

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What is the normal bandwidth required for a conventional fast-scan TV transmission using combined video and audio on the 70-centimeter band?

A. More than 10 MHzB. About 6 MHzC. About 3 MHzD. About 1 MHz

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What is the normal bandwidth required for a conventional fast-scan TV transmission using combined video and audio on the 70-centimeter band?

B. About 6 MHz

What type of signal is indicated by the term NTSC?

A. Normal Transmission Mode in a Static Circuit

B. Never Twice the Same Color C. Standard fast scan color TV signal D. A frame compression scheme for

TV signals

What type of signal is indicated by the term NTSC?

C. A standard fast scan color TV signal

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Which of the following is a form of

amplitude modulation? A. Frequency modulationB. Phase modulationC. Single sidebandD. Phase shift keying

32

Which of the following is a form of

amplitude modulation?

C. Single sideband

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What is the approximate bandwidth of a single-sideband voice signal?

A. 1 kHzB. 2 kHzC. Between 3 and 6 kHzD. Between 2 and 3 kHz

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What is the approximate bandwidth of a single-sideband voice signal?

D. Between 2 and 3 kHz

35

What is the primary advantage of single sideband over FM for voice transmissions?

A. SSB signals are easier to tune in than FM signals

B. SSB signals are less likely to be bothered by noise interference than FM signals.

C. SSB signals use much less bandwidth than FM signals

D. SSB signals have no advantages at all in comparison to other modes.

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What is the primary advantage of single sideband over FM for voice transmissions?

C. SSB signals use much less bandwidth than FM signals