Have you ever used a Walkie-talkie radio, and felt that there was something wrong with the particular radio that you were using or with the system because the range was reduced?  In addition, have you ever wondered why some Walkie-talkies seemed to have much further range than other Walkie-talkie radios on the same system?

A new VHF radio system that was recently installed for a public safety agency worked sometimes and sometimes not.  It had poor range with some of the Walkie-talkies, but great range with others.  It was the investigation as to why some of the units worked with a range of better than 20 miles, but others could not talk even 2 miles that generated the need for this article.

A radio system is made up of transmitters, receivers, antennas, antenna system peripherals and power supplies.  There are many books, articles, and courses available that cover each of these areas, but this article is concentrating only in the area of Walkie-talkie antennas, and as such, is staying on point about these antennas only.

The range of a radio system is influenced by quite a number of factors.  The factors that determine the range include:

• Transmitter Power
• Receiver Sensitivity
• Transmission Line Losses
• Antenna Gain
• Antenna Efficiency
• Antenna Height
• Line of Sight
• Obstructions
• Terrain
• Noise Floor
• RF Interference

In a well-designed radio system, the design engineer will have taken every one of these factors into consideration for that design.  Some of these factors are determined by the FCC rules and regulations, some by economics, and others just by the luck of the draw as to where the system is located.  In any case, the range of the system is the aggregate of all of these factors.

The items dealing with the antenna have the greatest effect on the range.  These few factors will have the most influence in determining the range of the system. 

Since the fixed part of the system, often referred to as the SYSTEM INFRASTRUCTURE, is constant for all users of that system, the individual mobile unit installations and Walkie-talkie antenna efficiencies will be the factors that determine which units have better range than other units.

There have been many articles over the years that cover the ins and outs of mobile installations, but there have been very few articles on Walkie-talkie antenna efficiencies.  The remaining parts of this article will only deal with Walkie-talkies and their antennas.

Just like any mobile or base radio station, portable Walkie-talkie radios have the same operating parameters that determine the range of that station.  The main difference is the external environment can change just by the operator turning around, where the radio is worn, or where his/her hand is placed in relation to the Walkie-talkie antenna.

The radio itself will have the same parameters that all transmitters have, including FREQUENCY, MODULATION LEVEL, POWER LEVEL, DISTORTION, and SPECTRAL PURITY.  The receivers will have the parameters of SENSITIVITY, SELECTIVITY, FREQUENCY, AUDIO OUTPUT LEVEL, DISTORTION, INTERFERENCE REJECTION, and SQUELCH LEVEL.  The factor that is rarely tested, but has a great influence on both the transmitting and receiving paths is the ANTENNA EFFICIENCY.

In order to correctly measure the above parameters of a radio, there needs to be a method where the proper test equipment can connect directly to the radio for the Radio Frequency (RF) interface and to the audio circuits for the remaining parameters.  All of the manufacturers have the required cables, connectors, and adaptors available to do this.

TRANSMITTER TESTS

It is important to be able to measure the actual transmitter output power of a Walkie-talkie.  In most cases, a conventional wattmeter tied to a Dummy Load or a Communications Service Monitor can be used to measure the power of a Walkie-talkie.  Most radios will be in the 3 to 5 watt range, but there are a few of them out there that only operate with 2 watts, while others can operate up to 7 watts.

If you have a 5-watt portable, and you are measuring only 4 watts, the difference of 1 watt is only 1 dB.  You will not have much of a range problem if your power is only down by 1 or 2 dB.  In fact, you will not be able to notice this at all in most cases.  However, if your power is down by 3 dB (50%) or more, then you do need to look further into this.  Remember to always read the radio specifications before you start tearing apart the radio, and have a fully charged known good battery on the unit before making these measurements.  Also, make sure your test equipment is working properly and you take into account any antenna test cables and connector losses.  It is amazing how many times a good radio is taken apart due to faulty test setups.

Once the power level has been tested, the same test setup can be used to measure the other transmitter parameters, including FREQUENCY, MODULATION, DISTORTION, and SPECTRAL PURITY.  Once you have verified that all of the transmitting levels are within specifications, then the receiver parameters need to be tested.

RECEIVER TESTS

The receiver tests insure that the Walkie-talkie being tested can receive the fixed infrastructure radio transmitters.  Again, there needs to be a method to directly connect the test equipment to the portable radio.  The sensitivity of a receiver is easy to measure, and if it fails to be within 3 dB of the published specifications, then you can test for some of the other parameters.  In addition, there are many test sets (Communications Service Monitors) that have an output specification of +/- 3 dB for the generator output, so it is possible for the receiver to measure 6 dB out of specification, and in fact, still be working correctly.  Know your test equipment before ripping apart and rebuilding your receiver.

In the old days, the SQUELCH control was always available for the operator to change so that weak signals could be received.  All of the newer radios have this as an internal setting, and at best, a MONITOR switch or pushbutton is provided on the radio.  Many times, the users are not aware of this option, even when it is in place on the radios.

In today’s technology, the receivers in the Walkie-talkies are full featured, with specifications that exceed the base and mobile units of the past, and are contained in a single IC chip half the size of your little fingernail.  With these specifications, it again falls on the antennas to work properly for the Walkie-talkies to have good reception.

SWR

This is the parameter that almost everyone misses when testing a Walkie-talkie.  It is easy to measure the transmitter and receiver parameters, but quite difficult to measure the antenna parameters.  In addition, the operating frequency of an antenna is determined by its length, combined with the ground plane of the radio, and the surrounding objects that will cause the antenna to operate at a lower or higher frequency, depending upon how far away the objects are from the antenna.  Because of this characteristic whereby an antenna is detuned by nearby objects, it can be designed into an antenna to actually be tuned to work better when worn on your belt, as opposed to operating in free space away from any object or person.  All of the Motorola Walkie-talkie antennas are designed for this factor.

In testing antennas for Walkie-talkies, especially for VHF radios, it is very important that the antenna always be at least 1 to 2 inches away from your body if the radio is worn on your belt, as the presence of your body being very close to the antenna for the entire length of the antenna seriously detunes the antenna where it actually disappears as an antenna.  It is not uncommon for the range to shrink to 1% of normal if the antenna does come in contact with your body.  Most of the radios on the market today have the antenna mounted to the case such that there is that distance, or have available leather or canvas cases that provide for the distance separation from your body.  Those of us who have extra handles in the midsection of our bodies must use the external cases or pouches, even on the radios that have the distances built into them.

If you want to see how well an antenna performs standing in free space compared to sitting just above your belt, the best way to measure this is to use one of the antenna analyzers such as the Anritsu Sight Master™ or the Bird Technologies Sight Analyzer™ with a phase stable cable, along with the proper adaptor to match the end of the phase stable cable to the antenna.

The first thing that you will notice is that the antenna is fairly narrow in the frequency range that it is tuned for.  Since the base station transmitter usually has a much higher output power than the Walkie-talkie, it is advantageous for the Walkie-talkie to be most efficient on the frequency that is normally used for transmitting from the Walkie-talkie, which will be the base station receive frequency.  Many of the radios have antennas that are not tunable.  In these cases, you must specify to the manufacturer or dealer what frequency you are using for your transmitter on the Walkie-talkie, and they will provide the correct band antenna for that frequency range.

In many systems, there may be channels that are available and used that are outside of the true operating range of the antennas.  In these cases, the range on these channels will be reduced from what is the true potential of the radio.  It is best to engineer multiple channel system so that the Walkie-talkie transmitter is operating on frequencies close to each other and in the band of the antenna.

FIELD INTENSITY

Field Intensity is a quantitative measurement that provides an indication of how much signal is radiated from a radio transmitter.  One of the laws of physics that prevails here is that as you increase the distance between the transmitter and the receiver, the field intensity drops by the square of the distance.  In simple terms, if you double the distance, you quarter the field intensity.  If you triple the distance, the field intensity will drop by a factor of 1/9 the original value.  If you quadruple the distance, the signal will be 1/16 the original value.  A second factor is the free space attenuation of radio signals.  The formula is:

            Attenuation (dB) = 36.6 + 20*(Log (D [miles])) + 20*(Log (F [MHz]))

This formula works for Line-of-Sight signals.  Any obstructions such as trees, buildings, vehicles, people, or any other item will attenuate the signal by some extent.  In this case, the body could block the antenna signal path to and from the base station site.  Also, if you do not have Line-of-Sight due to terrain obstructions, you will have severe losses between the transmitter and the receiver.  Finally, the curvature of the earth does prevent a signal from being Line-of-Sight over very great distances.

By performing tests in a controlled environment, it is possible to check if the radio and if the antenna are performing as desired and designed.  You do need to test both the antenna and the radio to ascertain if everything is working properly.  Just because something is new out of the box does not guarantee that it is working correctly. 

POWER

The transmitter power, along with all other transmitter parameters, is supposed to be tested any time a new station is placed into service.  In the US, all transmitters that put out more than 2 watts are required to have these measurements before a transmitter is placed in service.

SWR

In today’s technology, it is interesting that the wattmeter or antenna analyzer is quite a bit larger in size that the Walkie-talkie itself.  An antenna analyzer will give a graphical representation of the antenna performance, which is better than just looking at the reflected power on a specific frequency with a wattmeter.

Under normal circumstances, a SWR of under 1.5:1 which is equivalent to –14 dB return loss indicates a good match at the operating frequency.  A SWR of 2.0:1, which is equivalent to a –9.0 dB return loss, is the worst case that would be tolerated for an antenna to radiate.  At 2.0:1 SWR, the antenna is only operating at 90% efficiency, which is the bare minimum that an antenna should operate at.

Using field tests, it has been found that many of the antennas only operate within a 5 MHz window where the SWR is less than 2.0:1, and the antenna manufacturers normally label what the limits are on the antenna or by the model designation. 

In further testing, when the antenna that is tuned correctly, and has a good SWR on the normal operating frequency, is placed directly next to a body as would find when a Walkie-talkie is mounted on a person’s belt and the antenna is touching the body, the SWR goes from acceptable to terrible.  In the case of the public safety agency installation that brought this article to light, the antenna was detuned to the point that the antenna was operating at less than 1% efficiency.

In using an antenna analyzer, it was shown that just by moving the antenna away from the body by at least 1 inch, the antenna did behave as designed, and the SWR did return to the acceptable range.  In looking at different model radios made by different manufacturers, some, such as Motorola and Kenwood, have figured this out and the antennas are mounted such that they are removed away from the body even when there is no holster case and just the belt clip is used.  Other manufacturers and models within a manufacturers line have not realized this problem.  When these same radios were outfitted with the recommended holster cases by either the manufacturers’ product or an after-market vendor, the antennas are moved away from the body at the recommended distance of over 2 inches, and the radios did work as designed.  If a person does want to leave the radio on their belt, and use a lapel microphone, then the antenna must be away from their body by more than 1 inch, and preferably by 2 inches in VHF for the radio to work properly.  As the frequency goes up, the distance between the body and the antenna can be reduced.  VHF antennas need the most distance of separation, while UHF and above frequencies can be reduced to less than an inch for the antenna to continue to work properly.

FIELD INTENSITY

The ultimate way to determine if a radio and antenna combination is working properly and together is to test that the field intensity matches the predicted value for the power at a controlled distance.

When a Walkie-talkie radio is used without a lapel microphone, the radio is brought up to the face of the user, and the antenna is usually above the user’s head so that it does not matter which direction the user is from the base or repeater in which they are communicating with.  When a lapel microphone is used with a Walkie-talkie, the radio is directional in such a way that when the body of the user blocks the radio and antenna from the other user or repeater, the signal will be attenuated by some extent.  On VHF radio systems, this is present, but not to the extent that most users need to worry about it.  On UHF and above frequencies, such as 700 MHz, 800 MHz, and 900 MHz systems, the manufacturers of the radio systems put the antennas on the lapel microphones to lessen these directionality affects.  It was through the field intensity tests where the manufacturers determined that the lapel microphone antennas were needed for the higher frequencies as cited here.  Many of the UHF and above frequency systems use multiple receivers and a voting system so that the users in the field do not need to worry about what direction they are facing when using their radios.

Walkie-talkie radios have become the standard of communications for a lot of companies and agencies as the preferred mode of communications.  The radios have become very small, reliable, and user friendly.  The one component that has not changed over the decades is the antennas.  Due to the laws of physics, the antennas must be a certain length that corresponds to the frequency being used.  When the antennas are placed touching the body of the user, it will be detuned, and will no longer perform properly.  Just an inch or two away from the body will make the difference if the antenna works as designed for VHF radios, and less for the higher frequencies.  When your radio system fails to work as designed or expected, do not forget to look at the antennas of the Walkie-talkies as the problem. 

ANTENNA RESONANCE

All radio antennas have one thing in common.  The frequency of the antenna will determine the length of the antenna, and the length of the antenna will determine what frequency or frequency range in which it will work properly.  The relationship can be expressed using the mathematical formula of:

            FREQUENCY X WAVELENGTH = c

FREQUENCY IN HERTZ

WAVELENGTH IN METERS

c = SPEED OF LIGHT IN METERS PER SECOND

If the Frequency is expressed in Megahertz, then c = 300.  Professionals have been using this formula for decades.  Ham radio operators have been using this formula since the days of Marconi.

Once the WAVELENGTH has been determined by the formula above, the length of the antenna will be 1/4 of this length.  (It’s the law of physics and will just be accepted here.  Many books have been written on antennas, and this subject can be researched further for those that want to understand more about this.)

High-band VHF antennas (150 MHz) have a length of 18 inches.  UHF 450 MHz antennas have a length of 7 inches.  800 MHz radio antennas are 3 inches.  1900 MHz PCS antennas are just over 1 inch in length.  Antennas can be made to have gain, and these will be longer than these numbers.  Antennas can also be made physically shorter by coiling the lead around a wooden rod or other non-conductor.   The shorter the physical length, the less efficient the antenna will perform.

When the antenna is operated at the frequency that matches the wavelength, it is said to be at RESONANCE.  When the antenna is operated away from the resonance point, much of the signal will not be radiated, but will instead be reflected back to the transmission line and back into the transmitter.  The amount that is reflected can be measured, and this is expressed as either SWR or RETURN LOSS.  If the SWR or RETURN LOSS is too great, the antenna will not work, and can even damage the transmitter if the transmitter is not protected.  Most new transmitters will have a circuit that checks for excessive SWR and reduces the transmitter power or disables the transmitter if the SWR is too high.  Either way, the net result of having a high SWR is extremely poor performance of the radio.

LINK BUDGET

A 5-watt transmitter will have an output expressed in dB’s of +37 dBm.  The base receiver at a repeater site is typically at a level of –117 dBm.  This gives us a link budget for a 150 MHz system where the signal can be attenuated by 154 dB and it will still work.  Using the formula for attenuation, as found in this article, the Line of Sight distance could be up to 5,128 miles.

154 = 36.6 + 20 * Log (150) + 20 * Log (Distance)

117.7 = 20 * 2.176 + 20 * Log (Distance)

74.2 = 20 * Log (Distance)

3.71 = Log (Distance)

5,128 Miles = Distance

This is why very low power handheld radios can talk to satellites.  Back here on earth, the curvature of the earth, hills, trees, building, and other factors will greatly attenuate these signals to the point where you are lucky sometimes to just talk 15 miles on a radio system.  Add in metal buildings, and this can be less than 5 miles.

Ira Wiesenfeld, P.E., CETsr, WA5GXP has been involved with radio all of his working life.  He has worked in the broadcast, public safety, manufacturing, military, and consulting industries over the last 41 years, and has been active in amateur radio since 1963, where he holds an Advanced Class license WA5GXP.  He has a BSEE from SMU in Dallas, TX; is a Licensed Professional Engineer in the State of Texas; and is a Senior Certified Electronic Technician from ETA International.  He also has a General Radiotelephone Operator’s License from the FCC.  Ira is the author of Wiring for Wireless Sites and a few magazine articles on antennas and radio systems.  Ira can be reached at This email address is being protected from spam bots, you need Javascript enabled to view it