Entry Level Consumer and Amateur (Ham) Radio - Best Bands, Frequencies, Equipment

The objective of this article is to highlight only those frequency bands which permit affordable, practical, and easy operation. The emphasis of this article is only on those bands which are suitable for mobile or hand-held operation, and which will give a usable communication range.

Definition of a band

Thru the speed of light in vacuum, c, there exists a relationship between the frequency of an electromagnetic wave and its wavelength. The easy relationship to remember is that 300MHz is equal to 1m wavelength, with higher frequencies being shorter wavelengths. Therefore, 30MHz will be 10m, while 3GHz will be 10cm wavelengths, respectively.

Propagation Characteristics

The wavelength of the electromagnetic wave affects its behavior. Long wavelengths (100 meters or longer) can follow the curvature of the earth, so that the two antennas can be at different heights or geographical features. This wavelength can also follow topographical features such as mountains and hills, to some extent. At night, this wavelength can also reflect off the ionosphere, bounce down and up off the earth's surface, and travel a long distance.

Medium wavelengths, around 10m, are affected by the ionospheric propagation to a very large extent, since their ability to follow the curvature of the earth are more limited, and this direct route is not very long compared to the long wavelength.

Shorter wavelengths are primarily direct line of sight, and straight, communication paths. The two antennas should be able to "see" each other. Obstructions along this direct path will attenuate (reduce) the signal strength. Obstructions which are smaller that the wavelength will cause the electromagnetic wave to warp around the obstruction to some extent, while obstructions larger than the wavelength will usually cause absorption or reflection.

In general, for the same communication distance, as frequencies increase, the necessary antenna size and output power decrease to reach the same distance, because the energy content of an electromagnetic wave increases with increasing frequencies.

TODO LF, MF, HF, VHF, UHF.

TODO radio horizon to antenna height relationship.

Antenna Size

Omnidirectional (all directions equal in power) antennas of simple design must relate to the wavelength. Usually, the antenna is a quarter to a half the wavelength in size. The wavelength can therefore restrict the frequencies for handheld operation due to unwieldy antenna length.

Modulation

AM, or amplitude modulation, historically was the fist modulation scheme to be developed. A carrier wave, to which the receiver will tune to, is held to be a constant frequency, but the amplitude, or power, of the emitted electromagnetic wave is varied up or down based on the modulating input. The two advantages of AM modulation are 1) the low necessary bandwidth, which necessitates use of AM modulation at lower frequencies, and 2) several stations can be received at the same time by the receiver, which requires use of AM for critical applications such as ground to aircraft communication links. The public is familiar with AM modulation without knowing its meaning, when the 535 kHz to 1705 kHz public broadcast frequency range is referred to as the "AM Band", and labelled so on the radios.

A variety of phenomena in nature can sporadically affect the amplitude of background electromagnetic spectrum, and present itself as unwanted noise at the receiver. This phenomena includes lightning, electric motors, any sparks, including those in the internal combustion engine, fluorescent lighting, and so on.

FM, or frequency modulation, modulates the frequency of the carrier wave up or down. FM requires a much wider bandwidth compared to AM, but since few sources in nature can affect or emit changing signal frequency, the background noise which the receiver receives is much lower. Only one transmitter can be hear over FM - the strongest signal wins the receiver's attention.

In this article, frequencies lower than 50MHz will usually use Amplitude Modulation, while those higher than 50MHz will use Frequency Modulation.

Health and Safety Implications

The electromagnetic radiation affects the living organisms. Cells use low-power EM waves for signalling. Artificial, especially high-power, transmission can affect living organisms in several ways:

• EM radiation can cause heating of the skin or deeper tissues.
• EM radiation can interfere with cell signalling.
• EM radiation can cause damage at resonant frequencies. For example, microwave ovens excite and heat up water molecules at their resonant frequency of 2.4GHz, with a power output of hundreds of watts.
• EM radiation can cause damage (burns) to the retina (inside the eye) if a high-power antenna is looked at.

The author of this article recommends the following:

• Do not look directly at an antenna
• Do not use high-power handheld transmitters, and handheld transmitters in general. Use a vehicle-mounted antenna setup instead, connected to a handheld or mobile unit inside the vehicle.
• Do not use old, or rusty microwave ovens, as this can result in EM leakage from poor design or rusting seals.
• Do not press a cellular phone handheld against the side of the head. Use a wired headset or the speakerphone functionality. Texting uses short bursts of transmissions, typically away from the head, but results in meaningless conversations, in my humble opinion.
• The relationship between distance and EM intensity is an inverse square law. For example, at twice the distance from you to the antenna, the EM intensity will be four times less. Therefore, putting some distance between you an the antenna results in a significant lowering of the EM radiation intensity.
• Avoid use of wireless baby monitors. You are placing a low-power RF transmitter right next to a developing living organism.
• The author of this article strongly advises against the use of DECT wireless housephones, since the basestation and the handset are always transmitting, even when no calls are being made.
• Always follow sound usage principles when using RF equipment. This includes consumer devices such as cellular phones, Wi-Fi, Bluetooth, and other devices. For example, do not use a cellular phone as an alarm clock, and do not leave it next to your body at night. Use a dedicated alarm clock instead, and either turn the cellphone off, or place it into airplane mode at night. Use a wired Ethernet connection instead of Wi-Fi. Use a wired headset (with RF ferrite chokes to prevent the wire from becoming an antenna into your ear) instead of Bluetooth wireless headsets.
• Modern consumer RF equipment usually adjusts the power output to only the necessary level for an error- or noise-free operation. Therefore, allow the device the best communication path by not moving to the edge of available distance, by not obstructing the antenna (with hand for example), and by not degrading the signal (by either attempting to operate a cellular phone from inside a vehicle or by using other devices which interfere at the same frequency).

Tinnitus (ringing in the ear(s)) is a permanent or long-term adverse health condition. Do not use more audio output power than necessary. Do not use in-ear earbuds at high intensity.

Bands

We will explore the available frequencies to the consumer and amateur public in the order of decreasing wavelength, and increasing frequency.

Medium Frequency

"AM Band" 535 kHz to 1705 kHz, 560 to 180 meters

This band is one of two that every commercial radio can receive. The signal follows the curvature of the earth. Commercial AM transmitters at radio stations can have up to 50kW of power, and very tall radio mast antennas are used. During the daylight, reception by the consumer is possible up to 500 miles away. At night, the signal can bounce off the ionosphere and the earth, permitting a much longer range. Commercial AM transmitters lower their output power at night to not interfere with other distant transmissions.

Because the signal which the listener receives can consist of both direct wave (which followed the curvature of the earth), and the one reflected off ionosphere, the two (or more) can either cancel or reinforce each other, resulting in the "loudness" of the reception to vary up or down slowly, sometimes dropping below comprehension.

The range of modulating input is generally restricted to 5kHz, which is only acceptable for speech broadcasts. Only a monaural signal can be transmitted.

The consumer has experienced the specific wavelength nature of this band, without being aware of the causing effect. When driving thru a metal bridge (with metal sides extending up for structural reasons), the AM signal drops significantly, since the wavelength of the signal is much larger than the open spaces between the metal structural elements, and this prevents the signal from entering.

Cordless Phones

Old cordless housephones with telescoping antennas used the 1.7MHz band.

11 meters

Citizen's Band (CB)

Citizen's Band is located on frequencies from 26.965 to 27.405 MHz. This is commonly referred to as the 11 meters band. This band was very popular in the seventies, with popularity gradually waning. This band is very popular with truckers, who are typically found on channel 19. Channel 9 is the emergency use only channel.

While a large vehicle-mounted antenna allows non-line-of-sight operation, CB has several drawbacks:

1) The long wavelength makes handheld units to require long antennas for good reception, which is not always convenient.

2) Use of a handheld from inside the car is unfeasible (since the wavelength is much larger than the glass openings of the Faraday cage of the car's interior, a small portion of the transmitter's power will escape to outside of the car.

3) Use of a handheld or a mobile unit is greatly affected by the electromagnetic noise sources from the car's electrical system, such as the alternator, electrical motors, transients, spark plugs, and so on.

4) The license-free permission to operate in this band results in a lot of unregulated activity, such as poor equipment, swearing, lack of courtesy, and illegally high transmitter power.

Allowed output power: 4W. Typical size of antenna: TODO. Typical range: TODO

10 meters

10 meters is one of the Amateur Radio Bands. A license is required to operate in this band. The band generally extends from 28.300 to 29.700 MHz.

Business Band (10m)

Frequencies from ??? to ??? are part of the low-power Business Band allocation.

6 meters (50 MHz)

Baby monitors use the 49.830 - 49.890 MHz band. Cordless and RC toys use this band, as well.

Older cordless housephones with flexible antennas used the 50MHz band.

The Amateur 6m Radio band extends from 50.1 to 54.0 MHz.

Except for airplane communications, Amplitude Modulation is not used for frequencies higher than 50 MHz.

FM Radio Band (87.5 to 108.0 MHz)

The higher frequency (compared to the AM band) allows for a much wider modulating frequency range, to cover music and stereo transmission. There is also a lower background noise amount compared to the AM band.

The consumer has experienced the multipath characteristics of this band without being aware of the source. Often when the car is stopped at a traffic light, the FM radio signal unexpectedly degrades to a low amplitude or noise. However, creeping just a few inches forward restores the signal strength. The consumer is experiencing the multi-path wave interference, with a reflection off a building destructively coupling to a more direct transmission path.

Allowed output power: ?W. Typical size of antenna: TODO. Typical range: TODO

GMRS and FRS

GMRS stands for General Mobile Radio Service. Maximum permitted power is 5W, but a license is required to operate on this band.

Because UHF is line-of-sight, the theoretical range between two hand-held units would be two miles (3km). Mobile units have higher antennas and range of around 5 miles (8 km).

FRS stands for Family Radio Service. Frequency range is 462.5625 to 467.7125MHz. No license is required to operate on this band. These are the typical mass-retail clamshell "buy two" two-way radios. Output power is limited to 500mW. Antennas cannot be detacheable. The poorly-named "privacy channels" of a FRS radio help to eliminate background chatter from other operators on the same channel, but do nothing to ensure privacy of your communications.

Typical range is 1 mile (1.5km) with line-of-sight communication, out in the open, and without any obstructions in the path of the signal.

There are combination GMRS + FRS radio units available as well, however the user would have to be aware of the different power levels (5W and 0.5W) permitted, and about the licensing requirements to operate on the GMRS band (channels 1-7 on a "shared" band radio).

900MHz Band

Cordless housephones use the 900MHz band.

1.9GHz

Recently, 1.9GHz was allocated for DECT wireless housephones. The author of this article strongly advises against the use of DECT wireless housephones, since the basestation and the handset are always transmitting, even when no calls are being made. This presents health implications.

2.4GHz

The 2.4 GHz band is very crowded, with microwave ovens, Wi-Fi signals, security and video cameras, ZigBee devices, Bluetooth devices, baby monitors, and cordless housephones occupying.

The size of the wavelength can be apparent from previous discussions, without any calculations. I have discussed before how structures comparable to the wavelength can cause attenuation, reflection, or absorption. The consumer has seen the grid of the front door of the microwave oven many times, without thinking about why the grid is there. Since the holes of the grid are smaller than the wavelength, this, and not the glass, is what blocks most of the EM radiation from escaping outside the microwave oven internals.

5.8GHz

This band is used by Wi-Fi, and some handheld housephones, along with other applications.

Higher frequencies

WiMAX and point-to-point microwave links reside on higher frequencies still, up to tens of Gigahertz.

compare to WX, atomic radio

mobile station with 12V SLA or lithium batt pack

typical power, antenna size, distance

bands for taxi, police, fire, emt / EMS bands, etc

only covers handheld or mobile related bands and equipment, with usable voice capability

Yaesu, I-Com, Tin-Tac??

amateur general license

ARRL, local club

internet scanners

used equipment. Include links to e-bay, google shopping, custom craigslist search, amazon.

Mobile, car one is better

good antenna more important than fancy equipment