How to Improve Your FRS Radio Communications Range
(including a discussion on the new MURS radio service)
Copyright © 2001 by Stewart Teaze(N0MHS). All rights reserved.
This page discusses possible ways of improving the communications range of your existing FRS radios by constructing a base or repeater station. The options are presented in order from least to most expensive. In most cases, the more expensive options will provide the best performance.
Table of Contents
Introduction
"Echo" Repeater Station
Mobile FRS Base Station
GMRS Radio with Stock Antenna
GMRS Radio with Mobile Antenna
GMRS Radio with Base Station Antenna
MURS/FRS Crossband Simplex Repeater Station
Commercial Radio with Mobile Antenna
Commercial Radio with Base Station Antenna
Commercial Radio Crossband Simplex Repeater
Commercial Radio Interband Simplex Repeater
Introduction
Background
Before the Family Radio Service(FRS) existed, the only non-licensed radio services available to the public were Part 15 radios and Citizens Band(CB) radios. Both of these services left much to be desired, and this led the FCC to create FRS, and now MURS(Multi-Use Radio Service). Here is a rundown on all of the personal radio services, both licensed, and unlicensed:
Unlicensed Services
Part 15 Devices: Part 15 voice radios typically operate in the 49MHz frequency range, and are limited to 100mW of ERP(Effected Radiated Power), thru non-modifiable antennas. This is the same technology used by baby monitors, R/C vehicle control, and older cordless telephones. Those of who remember the "Batman" and "Barbie" walkie-talkies we had as kids, will recall how poorly these squawk-boxes worked. With some of the worst models, it was sometimes difficult talking to someone in the next room! Wireless ethernet cards, certain PDAs, and the newer spread spectrum portable telephones are also Part 15 devices. They operate on 900MHz or 2.4GHz, with a typical range limit of about 1000ft.
Citizens Band(CB) Radio Service: CB radios operate in the 27Mhz frequency range, small external base station antennas are allowed, and transmitter power is limited to 4W(AM),or 12W(SSB). CB became very popular in the mid 1970's. An entire culture grew up around CB radio, spawning new words in our vocabulary, and even leading to the production of Hollywood movies. As the popularity grew, the FCC responded by increasing the number of available channels from 28 to 40. Unfortunately, for a number of reasons, the CB culture is not conducive to family type communications. For example, obcene and indecent language is frequently encounted on the CB airwaves. Additionally, many CB enthusiasts use illegal power amplifiers, which they use to "drown out" the communications of legal users. Furthermore, the 27Mhz(11 meter) band is susceptible to atmospheric skip interference, which is greatly affected by the 11-year sunspot cycle; rendering most normal local handheld-based communications unusable for years at a time.
Family Radio Service(FRS): FRS radios operate on 14 frequencies in the UHF frequency band, in the 462-467MHz frequency range, with transmitter power output limited to 500mW ERP, thru fixed low-gain antennas. Unlike CB, the FRS UHF frequencies are unaffected by atmospheric skip interference. To avoid the "circus" atmosphere present on CB, and to make the FRS service more usable by families and groups, the FCC imposed very strict power and antenna limitations on the manufacturers of FRS radios. Unfortunately, these limitations leave FRS radios with rather anemic communications ranges.
Multi-Use Radio Service(MURS): MURS radios operate on 5 frequencies in the VHF frequency band, in the 151-154MHz frequency range, with transmitter power output limited to 2W, thru high-gain antennas with moderate height limitations. The MURS VHF frequencies are virtually unaffected by atmospheric skip interference. MURS radios will definately provide more performance than their FRS counterparts. In outdoor handheld applications, expect at least a 50% improvement in range. When communicating thru base stations, communications ranges of 10 miles or more will be acheivable.
For most people, the best way to improve their FRS communications range would be to pick up a set of nice new MURS radios. TEKK has the commercial-grade NT-10. Other options are to try to pick up the Radio Shack BTX-127 (19-1206) handheld unit ($29 on clearance), or the 19-1210 mobile ($49 on clearance), which can still be found, even in the year 2004, at a few Radio Shacks (usually the more rural, or out of the way ones). Look for new digital messaging offerings from Motorola in late 2004.
Licensed Services
General Mobile Radio Service(GMRS): GMRS radios operate on 23 frequencies in the UHF frequency band, in the 462-467MHz frequency range. Seven of the GMRS frequencies are shared with FRS. These frequencies are known as the "interstitial" frequencies. On the interstitial frequencies GMRS radios are limited to 5W ERP, thru antennas with moderate height limitations. On the non-interstitial frequencies, GMRS operators are allowed to operate thru repeaters, and with much more liberal power and antenna restrictions. A GMRS license costs $80, and is issued to an individual and their immediate family members. Expect a communications range of one to five miles with portable units and up to twenty-five miles with mobile, base station, and repeater units. NOTE: Manufacturers have begun to sell integrated GMRS/FRS radios at discounted prices (at Wal-Mart, etc.) - these radios have lousy integral antennas, and are typically limited to 2W output. Their performance is very poor (compared to a "real" GMRS radio), so don't believe their inflated claims of "up to 5 mile range" for these radios - it is simply a marketing gimmick used to trick the public into buying more radios and for a higher price.
Amateur Radio Service(ARS): Amateurs or "hams" are allowed to operate on a variety of bands across the entire radio frequency spectrum. Antenna and power restrictions are relatively minor, as such Amateurs are allowed to communicate over great distances using repeaters on VHF/UHF or worldwide using atmospheric skip on HF. However, Amateurs are restricted to communications of a non-commercial nature. To acquire Amateur operator privileges, it is necessary to pass a written examination covering radio and electronics theory, as well as radio operating principles. The entry-level Technician Class license consists of a 35-question, multiple choice examination covering basic priciples.
Radio Communications Range Primer
The Radio Horizon and Antenna Height
Radio communications in the VHF/UHF frequencies are basically limited to Line of Sight(LOS). Radio waves bend a little bit in the atmosphere, so the radio horizon is actually a little bit farther than the visual horizon. The general formula for calculating radio LOS distance between two stations is 1.4*sqrt(h), where h is the sum of the height of the two antennas above the average height of the surrounding terrain. What this means is that antenna height is the main factor in increasing your communication range. If you have enough power to reach the radio horizon, increasing your transmitter power will not significantly increase your radio's communications distance. REMEMBER - ANTENNA HEIGHT above average terrain is the main factor affecting your communications distance on VHF/UHF frequencies.
Transmitter Power
This is the amount of RF(Radio Frequency) power that your radio's transmitter produces. It is measured in Watts. Believe it or not, Transmitter Power is not that significant a factor in increasing your two-way LOS communication range. For example, if your radio transmits with significantly more power than the radio you are trying to communicate with, it will not help - at a certain distance, he will hear you, but you won't hear him. You will just end up interfering with all the other users on the frequency. This is why the FCC tries to design the radio services so that all the radios within a given service transmit with about the same transmitter power. Having a high Transmitter Power is good for the local AM/FM or TV stations, but it is generally bad on low-power two-way radio frequencies. REMEMBER - TRANSMITTER POWER is not a significant factor in increasing your two-way LOS communication range.
Antenna Gain
This is the amount of improvement an antenna will provide in the ability to transmit or receive energy in a given direction, over a standard half-wave dipole antenna. It is measured in decibels(dB). Antennas can be designed to "squash" the transmit/receipt pattern in a certain direction. This is equivalent to moving your antenna closer to the other station's antenna - thereby increasing both station's communication range! Unfortunately, FCC rules prohibit FRS radio manufacturers from affixing antennas that have any gain over a half-wave dipole, or from producing radios with easily-modifiable antennas; however, this is not a problem with MURS, GMRS, or ARS - as we are allowed to modify the antennas of the radios in those services. REMEMBER - Increasing your ANTENNA GAIN is a good way to increase your radio communication range.
Transmission Line Loss
Some of the RF energy your radio transmits and receives from your antenna will be lost in the transmission line between the radio and the antenna. Like antenna gain, this energy loss is expressed in dB. It turns out, that at the radio frequencies used by FRS radios, transmission line loss becomes a significant factor in your radio station's communication range. The longer the transmission line, the more the loss. As you recall, Antenna height is the main factor in improving communications range - we want to put the antenna up as high as possible, but we don't want to lose all the RF energy in the transmission line to the antenna. What do we do? Use high-quality, low-loss transmission line. This tends to cost more, but it is well worth it at UHF frequencies, when it comes to improving communication range. REMEMBER - TRANSMISSION LINE LOSS is significant at UHF frequencies, always use low-loss cables and connectors, and keep your cable run lengths as short as possible.
Receiver Sensitivity
The more sensitive your receiver is, the better it will be able to pick up signals. Sensitivity is typically given in uVolts for 12dB SINAD(SIgnal Noise And Distortion). This shows how much modulated signal you have to feed the receiver in order to reduce the noise and distortion by 12 dB. Receiver sensitivity is an important feature of your radio.
Receiver Selectivity
The ability to separate two closely spaced signals is a receiver's selectivity. The characteristics of the filter in the IF amplifier determine the frequency response of the IF stages and the selectivity. The narrower the filter pass-band, the "higher" the selectivity. The receiver pass-band should be tailored to the characteristics of the incoming signal. Too wide a pass-band and unwanted noise is received which detracts from the reception of the wanted signal. We use bandwidth to measure selectivity. This is how wide a range of frequencies you hear with the receiver tuned to a set frequency. Receiver selectivity is a very important feature of your radio. Radios with poor selectivity may be subject to the effects of receiver desense and intermodulation.
"Echo" Repeater Station
Description: Radio Shack sells this device. It is by no means a real radio repeater. The device is connected to the microphone and speaker jacks of the radio that will act as the "repeater". This device simply records each transmission, and later repeats the transmission, after a break in the transmission is detected. In a normal radio repeater, the voice of the person who has "possesion" of the repeater is immediately rebroadcast with no delay. With an echo repeater, it is unclear who has possesion of the repeater(as you don't immediately hear all other users of the repeater). To put it bluntly - the "echo" repeater is a bad joke.
Approximate Cost: $30
Range Improvement: 2x
Suitability:
Urban: 2 - If you can afford to live in the city, you can afford a better solution.
Suburban: 3 - Kids might find this slightly useful.
Mobile: 2 - If you can afford a car, you can afford a better solution.
Theme Park: 2 - Can you say "Mickey Mouse"?
Camping: 4 - This is about the only reasonable use for this device.
Rural: 3 - Again, kids might find this slightly useful.
Summary: Personally I would find this contraption annoying to use. It would also tend to confuse other listeners on the channel. There are those that feel that the use of this device is against FCC regulations - this is highly debatable, and it is doubtful that a user would face any consequences in any event. The only really good thing that can be said about the echo repeater is that it is cheap.
Mobile FRS Base Station
Approximate Cost: $80
Range Improvement: 1.3x
Practicality: Urban - 6, Suburban - 6, Mobile - 8, Theme Park - N/A, Camping - 7, Rural - 6
Under Construction
GMRS Radio with Stock Antenna
Approximate Cost: $150
Range Improvement: 1.3x
Practicality: Urban - 7, Suburban - 5, Mobile - 7, Theme Park - 8, Camping - 7, Rural - 5
Under Construction
GMRS Radio with Mobile Antenna
Range Improvement: 2x
Approximate Cost: $225 (GMRS Handheld Radio $150, Antenna $75)
Practicality: Urban - 5, Suburban - 6, Mobile - 9, Theme Park - 7(use stock antenna), Camping - 9, Rural - 6
Under Construction
GMRS Radio with Base Station Antenna
Approximate Cost: $300 (GMRS Handheld Radio $150,
Antenna/Feedline $150)
Range Improvement: 5x
Practicality: Urban - 2, Suburban - 3, Mobile - 6, Theme Park - 7(use stock antenna), Camping - 6(stock), Rural - 8
Under Construction
MURS/FRS Crossband Repeater Station
Approximate Cost: $500 (GMRS Handheld Radio $150, MURS Handheld
Radio $125, Antennas/Feedline $225)
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Introduction
The MURS/FRS Crossband Repeater System(MFCRS) provides an inexpensive method of allowing you to greatly extend the range of your MURS, GMRS(interstitial), or FRS radios. NOTE: Recent changes in the FCC MURS rules have made this system illegal to implement. At least I know that the FCC ended up making a rule change in direct response to this system design...
Most Commercial, ham, or GMRS radio repeater systems utilize a split-frequency system that is implemented on a single frequency band. As a result, costly filtering is required to avoid receiver desense. By utilizing crossband methods, costs are greatly reduced, as expensive filtering is no longer needed. By using simplex, rather than split-frequency, total system costs are further reduced, as more expensive split-frequency user radios are not needed - simple FRS and MURS radios will do the trick.
Please be aware that because this system utilizes inexpensive radio technology, it will be more prone to the effects of intermod. Depending on local conditions, these effects may vary from non-existant to very bothersome. If you live in a remote area, or plan to use this system on camping trips in the mountains, then you won't have to worry much about intermod. If you plan to put up one of these systems in a suburban environment, you may find intermod to be more of a nuiscance. A more detailed discussion of intermod and its effects can be found in the "Using Commercial Radios" section of this web page.
Setup
To set up an MFCRS, use a couple of VOX-capable single band radios(one MURS, and the other GMRS), and wire the headphone/speaker output into the VOX MIC input of each other's radio.
Users on one side of "the hill" would utilize one band(let's say MURS), and folks on the other side would use another band(let's say GMRS or FRS). By using separate bands, you eliminate the need for expensive filtering at the "repeater site".
Mount the two "repeater" radio's antennas high on the rooftop of your house, at opposite ends of the roof, and thru good high-gain omni antennas, and... PRESTO! you will be able to talk to other family members/friends on their cheap simplex GMRS/MURS/FRS radios at previously unthought-of distances! I would expect ranges from 3-20 miles, depending on local terrain conditions! Just make sure to use higher-quality, lower-loss, shorter run-length coax on the GMRS transmission line(as there is significantly more loss on the GMRS UHF frequencies, than on the MURS VHF frequencies).
This setup is the ultimate in inexpensive and non-intrusive range-extension...
Regarding the FCC Regulations and Interference Issues
The FCC FRS, MURS, and GMRS regulations were created with the intent of providing specific services to the public, while insuring that users of those services are protected from receiving, and prevented from giving, both intended and unintended interference. This repeater system utilizes radios that are approved for use in the FCC regulations for the intended services, and this goes a long way toward insuring that the system fits the intention of the rules - to not produce interference to other users. Used properly, there is no reason why a system like this would infringe on other people's right to use the Services as they were intended. Here are a few guidelines to insure that your system does not interfere with other users:
1) DO instruct users of the system to think of other users in their area, and monitor the frequency before transmitting.
2) DO monitor the frequencies in your area for a reasonable period of time, before putting your system on line. Certain frequencies are highly utilized and will obviously be bad choices to set up a Crossband Simplex Repeater. For instance; FRS channel 1 has become the defacto "FRS calling frequency", and is heavily utilized - bad choice! Certain MURS frequencies will have existing business users, even in suburban areas - these are also bad choices!
3) DO NOT use a commercial or ham radio(modified or unmodified) that uses a transmitting power much greater than the target service's maximum ERP(2W for MURS, 500mW for FRS). It makes no sense to transmit with much greater power than the user radio's transmission power - you can't communicate with a system that you can't hear. While your system will not work any better, it WILL end up interfering with many other radios that your system can't hear - possibly into the next county! This is CLEARLY an illegal system, and sooner or later you will be caught and dealt with. If you really need 25-50 Watts to work the repeater, then MURS/FRS-GMRS interstitial is NOT for you - consider setting up a split-frequency GMRS repeater, or getting an Amateur Radio license and set up a ham repeater(good luck coordinating a frequency in a major city!).
4) DO NOT use a commercial or ham radio (modified or unmodified) that uses a bandwidth greater than the target service's maximum bandwidth. You system will experience degraded performance, and will interfere with the communications of users on adjacent channels.
5) DO NOT build a MURS to GMRS non-interstitial crossover repeater. First of all, most current GMRS users are not keen on this kind of idea, and are on constant alert for "intruders"; so you will probably be reported to the FCC(unless you are in the backwoods somewhere). Second of all, this system would now be clearly against the FCC rules, as you would be obviously crossing between an unlicensed service(MURS) into a licensed-only(non-interstitial) portion of the GMRS service. (see the section below on REGARDING CONCERNS FROM HAMS AND GMRS NON-INTERSTITIAL USERS, for more information on this subject).
6) DO NOT use antenna gains much greater than necessary for your expected repeater user's needs. Not only will this cut down on the chance of interfering with other users, but it will cut down on the chance of other users interfering with your system's operations.
7) DO consider using directional antennas, when appropriate. Not only will it improve system performance, it usually will cut down on the chance for unwanted interference to and from other users.
Regarding Concerns from Hams and GMRS Non-Interstitial Users
Some GMRS non-interstitial users have voiced concerns about this kind of system because it would lead to GMRS becoming a virtual 2nd hobby service, and if that became the case, then GMRS would be inundated by entry-level hobbyists, and current GMRS user's level of service would deteriorate. These GMRS non-interstitial users have taken heart, up to now, in the fact that the FCC has asserted that they don't want to create a second hobby service, and do not want GMRS to become a hobby service. I can see where these gentleman are coming from, but I don't have any intention of "crossing" these users over to the GMRS non-interstitial frequencies. First of all, I, and I would assume most other "family-types", are only interested in crossing from MURS to FRS/GMRS-interstitial. Second of all, and in regards to the hobby question, I will be encouraging those users who have gotten a taste for the hobby aspect and wish to further explore radio experimentation, to get their Technician Amateur Radio License.
A couple of years ago, I submitted a proposal for a "communicator" entry level license to the FCC:
FCC Communicator Class License Proposal
Many of the ideas for this proposal came from feedback I received on the rec.radio.amateur.policy Internet newsgroup. This proposal received luke-warm response in the Amateur community, and it was eventually rejected by the FCC(even NCI(NoCode International) felt fit to criticize it - what a bunch of hypocrites). Since then, I have refocused my efforts into farming the FRS(and now MURS) users, and convert these young users to be hams, as the average age of hams is way too high, and the USA is losing the ability to teach the younger generation the radio art.
Look - young people need a place to experiment with radio. As silly as the old Amateur Novice license was as a entry point for young people(because of its outdated Morse Code requirement), the FCC's elimination of the Novice license has actually been A STEP BACKWARDS in providing young people a good starting point for radio experimentation.
Part of the result in not providing an easier starting point has been the 11 Meter "CB cesspool" debacle. These kids have been left unsupurvised there - what else do you expect. Instead of hams trying to work with the kids, they have turned ham radio into an "old boy's club". This was not the original intention of the service. That being said, I would much rather have a youth-oriented Amateur Radio Class created, than to have to use FRS/MURS/GMRS as the entry-point and bridge into radio experimenting. But right now, there is no alternative.
In any event, all this has caused me to rethink the privileges for the proposed Communicator License Class, and I now believe that they should be allowed have all the old Novice VHF/UHF privileges, plus and additional small slice of the 70cm band, so that they can inexpensively experiment with crossband operations.
Commercial Radio with Mobile Antenna
Approximate Cost New: $875 (UHF Radio $800, Antenna/Feedline $75)
Approximate Cost Used: $375 (UHF Radio $300, Antenna/Feedline $75)
Commercial Radio Base Station
Approximate Cost New: $1050 (UHF Radio $800, Antenna/Feedline $150)
Approximate Cost Used: $400 (UHF Radio $300, Antenna/Feedline $100)
Commercial Radio Crossband Simplex Repeater
Approximate Cost New: $1850 (UHF Radio $800, VHF Radio $800, Antennas/Feedline $250)
Approximate Cost Used: $750 (UHF Radio $300, VHF Radio $250, Antennas/Feedline $200)
Commercial Radio Interband Simplex Repeater
Approximate Cost New: $2900 (UHF Radios $1600, Antennas/Feedline $300, Filters $1000)
Approximate Cost Used: $1100 (UHF Radios $600, Antennas/Feedline $200, Filters $300)
Links
FCC Personal Radio Services Page
MURS Discussion Group
Building a Low-Cost Nationwide Wireless Network
MURS
PubCel Home Page
