SLIDE 12 7/25/2013 12
US Amateur Bands
- Bands: The physical wavelength of the radio wave is
used to identify the band (or group of radio waves with similar characteristics)
– 2-meters is most common (144-148 MHz) – 70-centimeters is growing in popularity (420-450 MHz)
- Technician class operators are allowed to transmit on
the bands shown to the right, which are VHF and UHF frequencies
- 50.0 to 50.1 MHz and 144.0 to 144.1 MHz are
restricted to Morse Code communication only
- Wavelengths above 10 meters (or frequencies below
30 MHz) are HF frequencies
Technician Amateur Radio License 45
Technician Class License Operating Privileges
Technician Class Amateur Radio License 44
Very Low Frequency (VLF); Low Frequency (LF); Medium Frequency (MF), High Frequency (HF); Very High Frequency (VHF), Ultra High Frequency (UHF); Super High Frequency (SHF); Extremely High Frequency (EHF) 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz
VLF LF MF HF VHF UHF SHF EHF Low Frequencies Long Wavelengths High Frequencies Short Wavelengths
VHF TV FM UHF TV Cell Phone AM Shortwave Radio Frequency (RF signals) Audio
Polarization
- Polarization is the orientation of the electric field of the radio wave.
A radio wave can be horizontally, vertically, or circularly polarized.
– Holding transceiver so that the antenna is vertical maximizes performance. This happens because the polarization of the radio waves match the antenna. – When VHF/UHF antennas are misaligned, the received signals can be dramatically reduced, as much as 100 times. – Horizontal antenna polarization is normally used for long-distance weak- signal CW and SSB contacts using the VHF and UHF bands. Horizontal polarization is preferred because it results in lower ground losses when the wave reflects or travels along the ground.
- For practical purposes, what factors most contribute to how far I
can talk on my radio?
– Wavelength of the radio wave – Signal strength or power – Obstructions in the radio wave path (buildings, hills, etc.) – Height and type of your transmitting antenna – Polarization of the radio waves (polarization matters)
Technician Amateur Radio License 46
Inexperienced users do not hold their radios vertical and substantially reduce their transmission distance by misaligning the radio wave polarization.
Propagation
- Propagation is the movement of
radio waves.
– Radio waves spread out from an antenna in straight lines unless reflected or diffracted along the way, just like light. – The earth seems less curved to radio waves than to light, therefore, VHF and UHF radio signals usually travel about 1/3 farther than the visual line
- f sight between two stations.
- The strength of radio waves
decrease as they travel farther from the transmitting antenna
- Radio horizon is the most distant
point to which radio signals can be sent directly without reflection
– In most cases it is the point where radio signals between two points are blocked by the curvature of the earth.
Technician Amateur Radio License 47
VHF and UHF radio waves are diffracted around the sharp edges of a solid object, such as a building, hill or other
- bstruction. Some signals appear behind the obstruction as a
result of interference between waves that are bent in different ways around the obstruction. The resulting interference pattern creates shadowed areas where little signal is present.
Knife Edge Propagation
Propagation and the Ionosphere
Altitude (miles)
Troposphere
170 140 70 60 30 6
Stratosphere D Layer E Layer F1 Layer F2 Layer
Ionosphere is composed
- f these layers
- Ionosphere is formed by solar ultraviolet (UV)
radiation.
– The UV rays knock electrons loose from air molecules, creating weakly charged layers at different altitudes. These layers can absorb or refract radio signals, sometimes bending them back to the earth.
- Reflecting Radio Waves: The ability of the
ionosphere to diffract or bend radio waves is dependent on numerous factors:
– Frequency of the radio wave – Intensity of solar radiation – Daytime or nighttime
- Meteor Scatter Propagation: A meteoroid
burring up in the ionosphere leave a meteor trail of ionized gas that can reflect radio signals.
– The best band for meteor scatter is 6 meters and contacts can be made at up to 1500 miles.
F1 and F2 combine at night improving the ionospheres ability to reflect radio waves
Technician Amateur Radio License 48
