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Frequency Spectrum

The answer to this question is dependent upon a number of factors which include the type of radio system you operate, where you are attempting to cover, how many repeaters or base stations you need to cover the required area, are you dealing with flat terrain or is it mountainous, are you trying to operate the radio system on an exclusive frequency, are you already licensed for an exclusive frequency, do you need mobile to mobile radio coverage or just mobile to base and where the different elements of the radio system are located.  Cost is another item that needs to be considered because everyone operates within a budget.  Is there a issue with the capital costs for equipment procurement and is there money in the budget for the on-going monthly expenses to pay for the radio system.  Radio system costs can include the following:

  1. Equipment procurement costs or monthly finance payments
  2. Base station equipment maintenance costs
  3. Subscriber unit maintenance costs
  4. Site rent for each base station or repeater
  5. Backhaul costs of operating a network
  6. Wireline control costs
  7. Installation costs

There is no simple answer to the question of which band is best once you consider the issues of cost, radio propagation, frequency availability, frequency acquisition cost, system type, owning the system or subscribing to an airtime service, need for mobile to mobile coverage, site availability, etc.

RADIO RANGE

Radio signals travel primarily line-of-sight from the transmitter to the receiver, passing through different obstructions along the path from the transmitter to the receiver.  Signal strength diminishes with the square of distance, to it you move twice as far away, the signal is ¼ the signal strength.  If you are 3 times as far, the signal is reduced to 1/9th of the signal.  In addition, there is another loss due to the frequency which increases with higher frequency.  (This does not include the physical objects in the path which creates more signal loss.)  The effects of radio propagation are different for each band.  Since radio coverage is essential, the consideration of propagation characteristics of the different frequency bands must be taken into account when choosing a radio system.

With any radio system, the range of the system is always a design consideration.  The item that affects the range of the system more than anything else is the height of the antenna for the repeater or base station above ground.  When we couple that with the height of the ground at the transmitter site above average terrain which increases the distance to the visual horizon and the radio horizon, the range of the radio system can change considerably.  However, that is not the only parameter that affects the range of a radio system.  System range is affected by the specific performance of the antenna including the antenna gain, the signal loss in the antenna cable, the power output of the transmitter, the filtering in the duplexer or master antenna system, radio interference from other transmitters in the area and the noise floor of the antenna site.

Terrain is a significant factor in radio propagation.  Flat ground is much easier to predict radio coverage than hilly terrain and is much easier to cover with radio signal.  When a radio signal passes through a hill, the earth (dirt, rocks, streams, etc.) that is in the direct line of sight path all add to the signal loss.  Once the received signal drops below the minimum threshold to operate correctly, the radios no longer can communicate with each other.  In hilly or mountainous terrain, this can happen in a distance of a few hundred feet while on flat terrain, it would take miles to have the same effect.

The atmospheric conditions also affect radio propagation.  Certain areas have different kinds of problems with radio propagation due to something unique about the area.  Sometimes it helps radios work better and sometimes it hinders the use of radio.  Different frequencies are affected differently by atmospheric conditions, so there is no simple answer as to how a signal will propagate.

The general rule of thumb is that if you can see it, you can talk to it.  The visual horizon is dependent upon your height above ground, so it will be a different distance depending upon your location.  If you were on completely flat ground without hills, buildings, bridges, streams or any other man made or natural structure, you could expect to talk to about 15% beyond the visible horizon, because the radio horizon is further than the visible horizon.

RADIO BAND DIFFERENCES

At VHF-Low Band which is 30-50MHz, the signals will bend more than any of the other bands, so coverage in a hilly or mountainous area is well served from a propagation standpoint by VHF Low Band.  However, VHF Low Band suffers from a lot of noise and static compared to the higher frequency bands (which is the reason that many VHF Low Band radios have a noise suppressor option) and the propagation is often affected by atmospheric propagation anomalies such as “skip” which causes the radio signal to be heard thousands of miles away during high sunspot activity periods.  This can cause you to hear co-channel traffic hundreds or thousands of miles away at times which can become a significant annoyance.  There are no exclusive frequencies on VHF Low Band, and when the “skip” causes you to hear others from a long way away, all of a sudden, the channel is very crowded.  Equipment for this band can be expensive due to the fact that VHF Low Band equipment is made in a very small quantity because this is the least popular band for land mobile radio.  Antenna filter technology for this band is very expensive because of the large physical size that is required due to the wavelength of the radio signal which is approximately 6 meters at 50MHz.  (This increases the cost of tower site rent due to the size of the antenna filtering equipment and the antenna.)  This makes the mobile antennas about 5 feet long which can be a problem for vehicles that have to park in an underground garage and the base station antenna about 13’ tall (with wide spacing requirements on the tower) which increases the tower site costs.  In addition, the radio performance is often adversely affected by large power lines and sometimes telephone wires on poles.  Portable radios on this band are few and far between and most radio manufacturers do not make a VHF Low Band portable radio.

VHF High Band which is 150-174MHz will also bend around hills, but to a lesser degree.  The noise and static are significantly reduced from VHF Low Band and the “Skip” that allows you to hear from hundreds or thousands of miles away does not happen very often.  Radio receivers rarely need a noise suppressor, so the option is usually not offered on this frequency band.  There is a tendency for some “ducting” of the radio signal to happen from time to time which causes one to hear radio traffic from a nearby area that is typically too far away to hear.  The antenna wavelength is approximately 2 meters at 150MHz which makes the typical antenna about 17” long which is far better on vehicles and portable radios.  The radio signal is occasionally affected by large power lines, but not often compared to VHF Low Band.  Portable radios are normally available in VHF High Band, but the antenna efficiency is typically poor on these portable radios because the radio body is small compared to the ¼ wavelength of 17” which is also the length of the antenna.  Since most people do not want a 17” long antenna, helical wound antennas are typically used which further reduces the antenna efficiency.  The longer wavelength of the radio signal makes signal penetration into buildings difficult with portable radios.  Exclusive frequencies are possible to obtain in this band, but there are no paired frequencies in the band (except taxi and the old mobile telephone frequencies) plus there is a lot of adjacent channel interference because the channels are 15KHz wide on 7.5KHz centers.  That means that the adjacent channel on both sides of your channel overlap your channel which causes big problems under many circumstances.  The lack of a standard band plan with a standard spacing between receive and transmit frequencies in VHF makes master receive systems difficult and expensive to build at the tower site if multiple channels are required.  The duplexers for a single channel take a lot of building space at the tower site and the need for another antenna on the tower instead of being able to connect to a master antenna system increases the tower site rent charge.  There is a wide variety of radio equipment available from many manufacturers and the radio equipment is reasonably priced, but the antenna filtering equipment is expensive.

The Inland Waterway Band which is 217-220MHz will also bend around hills, but to a lesser degree than VHF High Band.  The noise and static is further reduced from VHF High Band and the “Skip” that allows you to hear from hundreds or thousands of miles away rarely happens.  There is a tendency for some “ducting” of the radio signal to happen from time to time which causes one to hear radio traffic from a nearby area that is typically too far away to hear.  The antenna wavelength is approximately 1 ¼ meters at 220MHz which makes the typical antenna about 12” long which is far better on vehicles and portable radios.  The channels are 12.5KHz wide on 12.5KHz centers and all the channels are exclusive, so there are no licenses available in this band.  The radio signal is rarely affected by large power lines, but not often compared to VHF High Band.  Portable radios are normally available in 216-220MHz band, but the antenna efficiency is typically poor on these portable radios because the radio body is small compared to the ¼ wavelength of 12” which is also the length of the antenna.  Since most people do not want a 12” long antenna, helical wound antennas are typically used which further reduces the antenna efficiency.  The longer wavelength of the radio signal makes signal penetration into buildings difficult with portable radios.  Exclusive frequencies are the only channels in this band and all the channels are paired.  The duplexers for a single channel take a lot of building space at the tower site and the need for another antenna on the tower instead of being able to connect to a master antenna system increases the tower site rent charge.  The radio equipment available is very limited and priced accordingly and the antenna filtering equipment is expensive.

The Land Mobile Very Narrowband Channels which is 220-222MHz will also bend around hills, but to a lesser degree than VHF High Band.  The noise and static is further reduced from VHF High Band and the “Skip” that allows you to hear from hundreds or thousands of miles away rarely happens.  There is a tendency for some “ducting” of the radio signal to happen from time to time which causes one to hear radio traffic from a nearby area that is typically too far away to hear.  The antenna wavelength is approximately 1 ¼ meters at 220MHz which makes the typical antenna about 12” long which is far better on vehicles and for portable radios.  Channels are 5KHz wide on 5KHz centers and all the channels are exclusive, so there are no licenses available in this band.  Only very special equipment can operate on the band due to the very narrowband emissions required to operate on the very narrowband channels.  The radio signal is rarely affected by large power lines.  The antenna efficiency is typically poor on these portable radios because the radio body is small compared to the ¼ wavelength of 12” which is also the length of the antenna.  Since most people do not want a 12” long antenna, helical wound antennas are typically used which further reduces the antenna efficiency.  The longer wavelength of the radio signal makes signal penetration into buildings a little tough with portable radios.  Exclusive frequencies are the only channels in this band and all the channels are paired.  The duplexers for a single channel take a lot of building space at the tower site because of the 1MHz channel spacing and the need for another antenna on the tower instead of being able to connect to a master antenna system increases the tower site rent charge.  Mobile and portable radios are no longer available in 220-222MHz band as the manufacturers have ceased production of all the equipment.  The only equipment available for the band is used equipment.

The UHF Band which is 450-470MHz is less able to deal with the mountainous terrain than either of the VHF bands.  Signals are more line-of-sight than in the VHF High Band, so coverage into mountainous terrain is more difficult and needs more tower sites to get the coverage.  Radio “ducting” is less common than on VHF High Band, so it does not happen very often,  Antenna wavelength at UHF is about ¾ meter which makes the antenna about 6” tall.  This antenna length works well on vehicles because they do not have problems in most underground structures and the antenna length works well on portable radios.  The antenna efficiency is typically twice as good on UHF compared to VHF High Band because the length of the radio body is about the size of the antenna which acts as a good ground plane for the antenna.  The shorter wavelength if the radio signal increases signal penetration into buildings with portable radios.  Exclusive frequencies are difficult to obtain in urban areas and are easy to obtain in rural areas unless they are too close to an urban area.  The channels are 12.5KHz wide on 12.5KHz centers, so there is no frequency overlap between channels and you generally do not need to consider the adjacent channel when obtaining a frequency for operation.  (The FCC allows for licensing and operation of 6.25KHz very narrowband channels in the band on the existing channels and channels that are 6.25KHz offset from the regular channels.)   The radio signal is rarely affected by large power lines and is typically not affected by telephone lines on poles.  Interference from “skip” is very rare and the atmospheric “ducting” is not that common.  Exclusive frequencies are granted in UHF and the adjacent channels are not a problem because there is no frequency overlap between channels as with VHF High Band.  The band is broken into two sub-bands of 450-460MHz and 460-470MHz which allows for the frequency separation between receive and transmit of 5MHz which makes a duplex radio difficult to operate properly.  There is a wide variety of radio equipment available from many manufacturers and the equipment is reasonably priced.  UHF tends to be the best trade off of performance, antenna size, signal penetration into structures, equipment cost and availability.

The UHF T-Band which is 470-512MHz has the same propagation characteristics as the UHF band with minor exceptions.  Since the frequency is slightly higher than the regular UHF band, the propagation losses are slightly greater.  It is common for the radio equipment to be slightly degraded at the higher frequency so a 5 watt radio may only produce 4.5 watts at the high end of the frequency band.  Antenna performance is similar, but sometimes the antennas are slightly less efficient.  Radio “ducting” is less common than on VHF High Band, so it does not happen very often,  The antenna wavelength at UHF is about ¾ meter which makes the antenna about 6” tall.  This antenna length works well on vehicles because they do not have problems in most underground structures and the antenna length works well on portable radios.  The antenna efficiency is typically twice as good on UHF compared to VHF High Band because the length of the radio body is about the size of the antenna which acts as a good ground plane for the antenna.  The shorter wavelength if the radio signal increases signal penetration into buildings with portable radios.  Exclusive frequencies are difficult to obtain in the 11 urban areas where they are authorized for use and T-Band channels are not available at all in rural areas.  The channels are 25KHz wide on 25KHz centers (most channels have been converted to 12.5KHz narrowband or 6.25KHz very narrowband), so there is no frequency overlap between channels and you generally (but not always) do not need to consider the adjacent channel when obtaining a frequency for operation.  Most licenses are issued on this band and most channels are exclusive, so there are few licensing opportunities in this band, especially since the FCC currently has a freeze for new licensing due to the impending auction of the public safety channels.  The radio signal is rarely affected by large power lines and is typically not affected by telephone lines on poles. The band is rarely affected by large power lines and is typically not affected by telephone lines on poles.  Interference from “Skip” is a very rare occurrence and the atmospheric “ducting” is not that common.  Exclusive frequencies are granted in UHF and the adjacent channels are not a problem because there is no frequency overlap between channels as with VHF High Band.  The band is broken into multiple sub-bands of 470-476MHz (TV Channel 14), 476-482MHz (TV Channel 15), 482-488MHz (TV Channel 16), 488-494MHz (TV Channel 17), 494-500MHz (TV Channel 18), 500-506MHz TV Channel 19) and 506-512MHz (TV Channel 20) which allows for the frequency separation between receive and transmit of 3MHz which makes a duplex radio very difficult to operate properly.  Each of the 11 major metropolitan areas that are assigned T-Band channels have 1-4 of the TV channels assigned for use within a 50 mile radius of the center of the city as defined in the FCC rules.  There is a wide variety of radio equipment available from many manufacturers and the equipment is reasonably priced.  Older equipment was made in 2 sub-bands of 450-482MHz and 482-512MHz or 3 sub-bands of 450-470MHz, 470-494MHz and 494-512MHz.  Many manufacturers currently make radios that operate 450-520MHz which covers both UHF and UHF T-Band which tends to be the best trade off of performance, antenna size, signal penetration into structures, equipment cost and availability.

At 800MHz which is 806-869MHz, the mountainous terrain is typically fatal in making the radio system operate properly without adding a lot of extra locations with radio infrastructure which considerably drives up the costs.  In certain areas of the country, the 800MHz signal will not propagate well because the pine needles from pine trees are approximately ¼ wavelength long which acts like millions of antennas absorbing the radio signal.  This is especially true in the Pacific Northwest, but it can happen in other heavily forested areas such as The Eastern Sierras and The Rocky Mountains.  In addition, the higher frequency has more signal loss so the signal level with all other parameters being the same at a given distance from the transmitter is lower.  The antenna wavelength at 800MHz makes the radio antenna approximately 3” long, so the mobile antennas are unobtrusive and are easily driven into underground garage facilities and the portable radio antennas are much easier for the end user to handle.  The antenna efficiency is typically 80% or better, so the portable radios perform better than UHF portables most of the time.  The shorter wavelength also allows the radio signal to penetrate inside buildings easier so many times the 800MHz signal will work when the UHF signal will not work inside buildings.

Channel spacing is currently 25KHz with most radio systems operating wideband FM, but the FCC intends to allow licensing of narrowband on the 12.5KHz offsets which are channels in-between the existing channels.  Most licenses are issued on this band and most channels are exclusive, so there are few licensing opportunities in this band, especially since there is still a licensing freeze in portions of the country due to the re-banding effort by Sprint.  The radio signal is not affected by power lines or telephone poles except under very unusual circumstances and atmospheric “ducting” and “Skip” are typically non-existent.  Exclusive frequencies are commonplace in 800MHz, but if you do not have one, it is highly unlikely that you will be able to obtain one in an urban area.  Since the separation between receive and transmit is 45MHz for 800MHz band, the ability of the radio to operate duplex is generally good.  There is a wide variety of radio equipment available from many manufacturers at 800MHz and the equipment is a bit higher priced than UHF equipment.

At 900MHz which is 896-941MHz,the mountainous terrain is typically fatal in making the radio system operate properly without adding a lot of extra locations with radio infrastructure which considerably drives up the costs.  In certain areas of the country, the 900MHz signal will not propagate well because the pine needles from pine trees are approximately ¼ wavelength long which acts like millions of antennas absorbing the radio signal.  This is especially true in the Pacific Northwest, but it can happens in other heavily forested areas such as The Eastern Sierras and The Rocky Mountains.  In addition, the higher frequency has more signal loss so the signal level with all other parameters being the same at a given distance from the transmitter is lower.  The antenna wavelength at 900MHz makes the radio antenna approximately 3” long, so the mobile antennas are unobtrusive and are easily driven into underground garage facilities and the portable radio antennas are much easier for the end user to handle.  The antenna efficiency is typically 80% or better, so the portable radios perform better than UHF portables most of the time.  The shorter wavelength also allows the radio signal to penetrate inside buildings easier so many times the 900MHz signal will work when the UHF signal will not work inside buildings.  Channel spacing is currently 12.5KHz with most radio systems operating narrowband FM.  Most licenses are issued on this band and most channels are exclusive, so there are few licensing opportunities in this band.  In addition, the FCC is converting approximately 60% of this band to broadband under a new ruling.  The radio signal is not affected by power lines or telephone poles except under very unusual circumstances and atmospheric “ducting” and “Skip” are typically non-existent.  Exclusive frequencies are commonplace in 900MHz, but if you do not have one, it is highly unlikely that you will be able to obtain one in an urban area.  Since the separation between receive and transmit is 39MHz for the 900MHz band, the ability of the radio to operate duplex is generally good.  There is a reasonable but more limited variety of radio equipment available from manufacturers than 800MHz and the equipment is a bit higher priced than UHF equipment.

SUMMARY

There are significant differences between various bands in the radio spectrum due to both regulatory issues and natural propagation issues.  Each of these issues has an effect on the use of the spectrum and one must evaluate these differences to determine which spectrum band best serves the needs of your organization.

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