Repeater Coverage
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Repeater's Coverage
By Larry Kuck
Our repeater system has a fair reach for its being at ground level. A repeater, as with any radio station, can hear as far as the eye can see, or in other words, over a line-of-sight distance. The higher the antenna is above the ground, the farther it will reach, to a more distant horizon.
The 440 MHz repeater tends to peek around corners and fill in some dead spots encountered on 147.12, as I have heard it told, from a mobile perspective. The shorter-wavelength signals tend to reflect off of large surfaces like downtown tall buildings, thereby filling otherwise shadowed areas. Once we get it running with the commercial-grade "Big Boy" repeater, which will run about 50 watts, and putting it on an equipment par with the 147.12, it should really be heard.
For best user performance
Repeater performance varies, depending on the type and location of the user's antenna and surrounding terrain, factors which become more critical as distance from the repeater site increases.
If one is within a mile to two miles from the repeater, one can enjoy the benefits of a handheld transceiver, its small size, low power consumption, and portability, and still put a good signal into the repeater, possibly even from inside of a lath-faced stucco house. Other users can enjoy listening to clean audio and a lack of noise and drop-outs during this user's transmissions.
The greater the distance from the repeater site, the more challenging it becomes to put a good signal into the repeater and avoid noisy and intermittent reception for other users. The positioning of the handheld transceiver, with its built-in antenna, becomes more critical, requiring the user to stay in one location once the "sweet spot" is found. At greater distances, this sweet spot may be so small that just moving the radio from where you can see the S-meter's bars on the display to where you can speak into it has put its antenna into a dead zone.
The antenna is the most important part of a successful amateur radio communications station. Therefore, if one uses a handheld radio at greater distances than maybe three miles from the repeater, one should invest in an aftermarket rubberized antenna that was designed with more gain than a stock antenna.
Estimated coverage range
Handheld
This is not my recommended choice for the one-and-only radio equipment a new ham is going to start out with. Why, you ask? It has a built-in antenna, which does not offer the best in antenna height or antenna gain, the most important ingredients to success. A handheld is a good second radio, but please, if you can swing it, get at least a mobile transceiver and a power supply for home use.
Having said that, a handheld transceiver will give access to a ground-level repeater while out in the open, for a range of 5 miles or more. Many factors enter into this picture to reduce the effective range. A location inside a car, or inside a house may shorten the range that you can achieve, especially a mobile home or stucco house or one with aluminum siding. The cab of a pickup truck may work out better than the cab of a passenger car, in part because the truck is higher-built and is surrounded on all sides with windows. Terrain between your location and the repeater may limit your range, as well as the seasons and the weather.
It has been observed that summertime signal path loss is generally greater than wintertime path loss. This means that the signal from your radio will arrive at the repeater with less strength in the summertime and stronger in the wintertime, without you doing anything different. Some natural factors include the following: More green foliage in the summertime will tend to absorb RF energy, creating loss, and wintertime temperature inversions and cloud cover may help to hold signals in closer to the ground, boosting signals, I have personally observed this phenomenon with regard to the five-mile distance between my home and the repeater site.
Seasonal noise floor changes have also been observed. During hot dry weather of summer, overhead power lines tend to give off more noise, whereas these same lines are less noisy after a washdown from rain. The noise floor at a repeater site governs what minimum signal strength is required to be heard and repeated. A noisy frequency is going to require greater signal strength from the user to quiet the noise.heard.
Because the terrain falls away toward the southwest from the repeater site in northeast Mesa, people may well hit the repeater with a handheld as far away as 20 miles, but coverage is very spotty except if the operator is out in the open. With the repeater at 200 to 300 feet higher elevation, areas downslope from the repeater will see some improved coverage.
Improving a handheld
I have touched upon this topic already, but it bears repeating: The antenna is the name of the game. To improve your range with a handheld, an aftermarket longer flexible antenna will increase your signal penetration and widen your sweet spots. Or use of a 5/8 wave mag-mount mobile whip on a cookie sheet will greatly improve your chances to be heard. Use of an antenna extension cable that lets you suction-cup-mount your rubber duck on the outside of your vehicle will even go a long way to improving your range -- I don't know what the product is called, as I was once given one without the packaging, but positioning it at the roof line of the cab of my truck gave me a good ground plane for the rubber duck! (That's what these rubberized flexible antennas are called, by the way.)
If you are parked somewhere, and you have nothing but a handheld with its rubber duck, set the radio on the roof of your car and speak into it. Positioning six to twelve inches may go a long way to finding a stronger signal in reception from the repeater, which generally translates to stronger transmission to the repeater.
Another trick is to hang a 19-inch wire for 2 meters or 6½ inch wire for 440 MHz, from the outer shell of your antenna connector. Antennas West sells one they call the Tiger Tail, which was nothing more than a piece of insulated wire, with a washer on one end that fits over your antenna connector, and then your duck screws on to lock it in place. The antenna may be a snug fit now with that washer under there. The far end of the wire had a plastic end cap on it to cover the bare end of the wire. You can make one yourself, just tying bared wire around the connector shell before placing the antenna. The hot pin in the antenna connector is inside the shell, and your wire addition will not come close to that.
One last thing you can do is to connect a home station antenna to your handheld. If you live in a downtown area, or near a broadcast center like South Mountain, a large base antenna will possibly swamp your receiver front-end with out-of-band RF energy from many radio services. This would cause you to hear police, taxicab and mobile phone services or ham repeaters that are not on this frequency. The physical size of the radio does not allow for the necessarily large components of a good band-reject filter to be included.
Mobile or Home Station gear
Home stations will typically reach our repeater from a distance of 40 to 60 miles, Antenna-challenged stations should be able to reach the station from at least 20 miles with less than 5 watts, and with a boost in power to maybe 30 watts, that should increase the readability of signals received by the repeater to a distance of 40 miles. Antenna-gifted stations may reach to more than 90 miles.
There are people in Phoenix who have access to Flagstaff mountaintop repeaters and TV channel 2, whereas the terrain blocks that direction from the Mesa area. Our repeater can be hit by a mobile stopped at just the right spot along the highway going west out of Payson along the Mogollon Rim, but that type of coverage rarely serves any useful purpose.
With a decent antenna in the clear, 15 to 25 watts will cover perhaps 50 to 90 miles, depending on terrain. Fifty watts will do just about all you will ever need for repeater voice communications from the home or car.
There are power restrictions on the 440 MHz band of 50 watts in Arizona due to military radars, but 50 watts from a good mobile antenna will work the repeater as far as you can hear it.
Having said all of this, don't sell yourself short on the capabilities of one or two watts of power! With a good antenna, and a decent location, you can work the Metro Phoenix area with just that much power. keep power levels to a minimum, because the more people there are on the band running 40 or 50 watts when one or five will do, the higher the noise floor is for someone else trying to hear something. It all comes back to that swamped receiver front-end, and less enjoyment by many if too many are running more than the minimum necessary power, which is addressed in the FCC Rules. I will one more time re-iterate: A good antenna trumps high power. You can do more with less if you have a good station antenna, and do less harm along the way.
First rig: Mobile or handheld?
The only difference between mobile and home station transceivers is that a 12 volt power supply has to be added to a mobile rig to run it at home. The home station usually has a built-in 120 volt AC power supply included.
These radios have the physical size required to contain the circuit components necessary to reject out-of-band signals that hamper the use of the handheld radio on a big antenna. The handheld may also have a hotter receiver, in order to perform reasonably well using that stock rubberzied antenna, which is designed more for portability than performance.
Use of any kind of outside antenna will get you around the VHF and UHF repeaters, with an easier signal to be heard. There really is no need to have 50 watts if you have any decent antenna. All that extra power will do is cause your neighborhood hams more interference potential to what they want to listen to on the same band. And 50 watts into an indoor antenna can cause significant interference to other electronics in the home or next door.
Power versus antenna
With 65 watts of power into a 20-foot high antenna versus 15 watts into one at 70 feet, the fifteen watts is going to outperform. That was demonstrated by a station in Deer Valley, who recently accessed our repeater. With that said, it doesn't require a 70-foot antenna structure nor more than 30 watts to be solid into several area repeaters. The antenna is the ace in the hole that trumps power every time.
A good signal can be had into our repeater with as little as one watt into an antenna with good gain over a distance of 30 miles if your location is out in the open. A tenfold increase in power, to ten watts will fill in the gaps and achieve more reliable access from greater distances out, and result in a 10dB signal increase.
By selecting an antenna with 3dB more gain, your power has suddenly been effectively doubled. A higher gain antenna makes more efficient use of the power your transmitter has, by concentrating the signal in all directions toward the distant horizon rather than being wasted skyward. A directional beam can further concentrate power in a single direction.
Locating an antenna as high as possible and in the clear as possible, whatever you choose to use, will give you maximum range from your location. If you cannot locate in the clear, you may benefit from positioning, six inches to a foot one way or another.
Mobile stations with a good antenna, best located in the center of the roof, but can be on the hood or rear deck, will reach the repeater over a range of 20 to 40 miles depending on power, antenna and location factors. There are high places where the mobile can reach from 70 miles away or more. We once had a 180 mile round trip through the 147.12, between central Tucson and Wickenburg. The Tucson station just happens to be in the right place with a beam and an above average power capability, and the Wickenburg station was a movile sitting in a high, clear place 90 miles away.
Indoor antenna
Use of the home rig on an indoor antenna can present some challenges. Typically, if you are running any kind of power into an antenna stationed next to the radio equipment, the power supply may shut down, or there could be undesirable audio distortion because of RF energy swamping the radio's circuitry. Other problems may cause out-of-band transmission of spurious signals.
The solution is for the antenna to be placed as far away from radio equipment and people as is feasible, or for radio and people to be placed as far away from the antenna as is feasible while in use, and with the antenna near a window. A mobile whip on a mag mount must be placed on the roof of the car, or something similar, such as a cookie sheet, a filing cabinet, a refrigerator. Not just for the magnet to stick, but for the counterpoise the sheet of metal provides. Even aluminum foil will work, except that the magnet won't stick.
Antenna discussion
Omnidirectional antennas can achieve more gain by concentrating signals toward the horizon at the expense of signals that travel uselessly toward the sky. Examples of omnidirectional antennas include the stock rubberized antenna on a handheld transceiver (poor), a longer optional rubberized antenna (better), or a full-length quarter-wavelength antenna (also better).
The full-length quarter-wave is 19 inches long on 2 meters, about 13 inches on 220 MHz, and 6.5 inches on 440.
Higher-gain omnidirectional antennas include the half-wave and the 5/8 wave. The half-wave antenna is less dependent upon a groundplane than are the quarter-wave or the 5/8 wave, but these antennas are longer and have more gain than a quarter-wave.
There are even higher-gain omnidirectional vertical antennas out there that can reach six feet to 20 feet in length, consisting of half-wave-over-half-wave and other similar co-linear designs.