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
9
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)
10
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.
11
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
12
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.
13
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
14
Recognition and correction of
problems (cont)
If a "Part 15" device in your neighbor’s home is causing harmful interference…..
15
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
16
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.
17
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
21
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
22
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
27
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
28
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
31
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
33
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
34
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.
36
What is the primary advantage of single sideband over FM for voice transmissions?
C. SSB signals use much less bandwidth than FM signals
Top Related