Lessons Learned About Frequency Sharing in the Amateur Radio Service

1
Lessons Learned About Frequency Sharing in the
Amateur Radio Service

• Gregory D. Lapin, PhD, PE
• American Radio Relay League

2
For Most Communications,The Paradigm is Shifting
From

• Each communicator/broadcaster is assigned fixed
  frequency channels.
• No one else uses an assigned channel except the
  licensee.
• Channels are reassigned geographically based on
  expected propagation.

3
Toward the Paradigm Upon WhichThe Amateur Radio
Service Is Based

• The Amateur Radio Service is assigned relatively
  small bands of frequencies scattered throughout
  the spectrum to experiment with propagation.
• Groups of frequencies are specified for different
  communications modes.
• Licensees are given the right can use any
  assigned frequency as long as they do not
  interfere with other licensees.

4
The Amateur Radio Paradigm

• All licensees have an equal right to use all
  frequencies.
• No frequencies are permanently assigned by
  regulation for anyone or for any purpose.
• Some frequencies have permanent assignment by
  agreement (via a frequency coordinator).
• Emergency communications always have priority.
• Hams have nearly 100 years of experience in
  refining this type of operating.

5
In the beginning
There wasSpark Gap the original UWB
No crystals, no filters just raw RF power
Circa 1910
6
Frequency Sharing Was a Challenge
King Spark ! Grown now to full maturity,
Glorious old sparks!Night after night they
boomed and echoed down the air lanes.Night after
night the mighty chorus swelled , by ones, by
twos, by dozens,until the crescendo thunder of
their Stentor bellows shook and jarred the very
Universe! A thousand voices clamored for
attention.Nervous, impatient sparks, purring
petulantly.Clean-cut business-like sparks
batting steadily along at a thirty-word clip.
Survival of the fittest. Higher and higher
powers were the order of the day. The race was
on, and devil take the hindmost. Interference.
Lord, what interference! Bedlam! Well, it could
not be Utopia. -Arthur Lyle Budlong excerpted
from The Story of the American Radio Relay League
7
The Solution

• In the 1920s, trans-Atlantic experiments with
  narrowband CW transmissions showed that they
  could coexist in the same frequency band without
  interference.
• 50 CW signals could occupy the same frequency
  space as one spark gap signal.
• A 5-watt CW signal could be heard over a greater
  distance than a 500-watt spark gap signal.
• By 1924 spark gap had virtually disappeared.

8
Amateur Frequency Allocations
9
Lessons to Avoid Interference When Sharing
Frequencies

1. Listen before transmitting.
2. Ask if the apparently unused frequency is
   actually in use.
3. Keep transmissions short.
4. Use minimum power necessary.
5. Different stations trying to use the same
   frequency should be able to understand each
   other.
6. Coordinate frequency use by other means (such as
   a common control channel or the Internet to
   schedule a frequency and time to communicate).

10
Why Listening to a Frequency Isnt Enough
B
C is talking to B A listens but does not hear
C A starts transmitting and interferes with B
trying to hear C
A
C
11
Regulations and Agreements

• Regulations specify which frequencies can be used
  and which modulation modes can be used on them.
• Band Plans are agreements that set aside specific
  sub-bands of frequencies for specific modes.

12
Limitations of Regulations

• Regulations allow different modulation modes to
  be on the same set of frequencies.
• How can one ask if a frequency is being used if
  everyone doesnt understand the question?
• Solutions to this include agreeing on Band Plans
  and Frequency Coordination.

13
Some Modulation Modes That Band Plans Specify

• Digital Modes
• CW QRP
• CW
• SSB, SSTV and other Wideband Modes
• SSB QRP
• Experimental
• Beacons
• AM
• RTTY
• DX Window

• Packet
• Satellite Downlinks
• Satellite Uplinks
• FM Repeater Inputs
• FM Repeater Outputs
• Auxiliary Links
• FM Simplex
• Radio Remote Control
• Amateur TV
• Earth-Moon-Earth
• Experimental
• Spread Spectrum

14
A Modern Amateur Radio Experiment in Frequency
Sharing

• WiFi (IEEE 802.11b) format and technology is
  leveraged to provide High Speed Multimedia
  networking on Amateur Radio frequencies.
• Off-the-shelf hardware is connected to innovative
  antenna designs with higher power as permitted
  under Amateur Radio regulations.
• Details at http//www.arrl.org/hsmm

15
My Favorite Story of Cooperatively Sharing a
Frequency