WSHC539

HOW MANY FARS??? One of the most asked questions about GMRS radios is “How many FARS?”. How far can it transmit and receive. Unfortunately, the question is someone meaningless as the answer is, “It depends”. Of the three primary factors, (power, antenna type and height) it is the height of the antenna by far that is the most important. It takes very little power and only the simplest of antennas to reach over 400 miles! While this topic has been covered before, most OPs make a mistake with the use of the earth's curvature equation. So here goes. Feel free to comment. The best example I could find on "How many FARS?", is from weather balloons which transmit in the 400 to 406 MHz range with an output power of LESS than 0.5 watts (60 to 250 mW) to a quarter wave ground plane receiving antenna. With a release point in Santa Cruz CA, the longest reception was ~750 km (466 miles) off the coast of Mexico. My personal best was 44 miles using a bubble pack Motorola Talkabout T7200 HT putting out 1.5 watts through an integral fixed antenna to a roof mounted J-pole antenna using Radio shack RG58 cable attached to a simplex repeater and a 4 watt HT. My view is that if you can’t hear with a FRS bubble pack radio in an open air, line of sight condition then there is some form of obstruction between the two radios. I consider that there are three types of obstructions. The first is the curvature of the earth, the second is a solid obstruction such as solid earth from a ridgeline, mountain, etc. to a reinforced concrete wall, and the third is vegetation, wooden structures, glass, human bodies, etc. The first two types of obstruction are absolute. You are not going to get a radio signal through no matter how much power or antenna type you are using. Only antenna height can solve the solid obstruction problem. It’s the third type of obstruction where antenna type, height and transmit power come into play. CURVATURE OF EARTH With an antenna height of 5 ft. above the ground that is flat you can transmit for 2.7 miles before the signal hits the earth from its curvature. But wait, if the other radio is also 5 ft. about the ground they also can transmit 2.7 miles for a total range of ~ 5 miles. These are the conditions for the normally stated 5 mile range of GMRS radios. The 7 miles that is sometime stated is a special case of both radios (~ 5 ft. above the surface) being over a body of water which slightly bends the radio signal giving a bit more range. Both cases also require open-air, line of sight conditions with both radios being at the same elevation. The condition that both radios are at the same elevation, which almost never is true, is why you can’t use these simple calculations for determining radio range from the earth’s curvature. In one YouTube video on FARS, the second scenario shown was with one radio located in Plankton (Elev. 922 ft) and the second in Melrose (Elev. 856 ft), OH. A distance of 4.6 miles apart. The reason you can’t use the above calculation of 5 miles horizon curvature range is that the town of Melmore is at an elevation that is 66 feet lower than Plankton even though it looks fairly flat. Not to get too much in to the specifics of the math, I take the difference in elevation (66 ft.) along with the height of the upper antenna (5 ft.) to compute a radio horizon curvature range, or 10.4 miles. I use this value as an approximation of how close I am to failing the curvature test. Don’t use GPS elevations as their accuracy is only +/- 60 - 100 ft.) For comparison purposes so one can better understand the importance of antenna height here are the earth curvature ranges for different antenna heights with a flat surface. (No consideration for the second radio antenna height above the ground). Use these values to help one determine approximate changes in antenna heights to reach the second radio. 5 ft. – 2.7 miles 10 ft. – 3.9 miles 20 ft. – 5.5 miles 30 ft. – 6.7 miles 50 ft. - 8.7 miles 100 ft. – 12 miles 500 ft. - 28 miles 1,000 ft. – 39 miles 5,000 ft. – 87 miles 10,000 ft. – 123 miles With my personal best I was ~ 4,500 ft. above the second antenna or a curvature range of around 82 miles. SOLID OBSTRUCTION Topographic features of the earth (the earth is seldom flat) are more important than the earth’s curvature in determining if you can communicate with another GMRS radio. To determine if you have any geologic solid obstructions you need to be able to construct a topographic/elevation profile using the USGS National Elevation Dataset (NED). You simply draw a line between the two antennas and have the software compute a profile. I use the software TOPO which is no longer available. You can also use Google Earth Pro to perform the same function. This will show you if you have an open-air line of sight or if the ground is going to obstruction the signal. Here is the profile from my 44 mile test sitting on Bandera Mt. and talking back to my house in Seattle. Easy peasy. To show you another example I was recently driving around the San Rafael Desert in SW Utah where there is no cell phone coverage. Computing various profile lines I was able to predetermine that if I set up a simplex repeater on a plateau near an easy access dirt road (the right-side or eastern line) I could communicate back to the hotel in Green River (38 miles away) from pretty much anywhere in the desert and some of the slot canyons in the San Rafael Reef which opened out onto the desert. A worthy undertaking as the soft sand made travelling somewhat sketchy. The profile line to the left (west) showed that the two radios could not communicate. Here are the results. This third example shows Google Earth Pro using the towns of Plankton and Melmore, OH. To see if one has any topographic issues simply draw a straight line (or place a straight edge on the computer screen) to see if you will intersect the earth. In this example the answer is yes, but check the elevation scale (7.5 ft) and by raising the upper antenna (Plankton) up to 15 ft. above the ground will allow you to communicate to the center of Melmore. It’s almost always best to raise the upper antenna for best chance of improved reception. Notice that there are a number of creeks and other low points that one will not be able to communicate into. I tried another profile line to see if one can communicate from the town of Plankton to the nearby #103 Highway. The answer is there is a low ridgeline (Elev. 935 ft.) that prevents this. By dragging the profile line you can find where the highest point is (the big red arrow). This is the location one would want to put up some form of a repeater if you wanted to extend the range of your radio. Semi-obstructions These are the types of obstructions where radio power and antenna type can help extend the range (FARS) of GMRS/UHF radios. Unfortunately, there are no formulas that I know off that will allow you to predetermine how many FARS a radio can transmit/receive under these variable conditions. Just don’t stand between the radio antennas and try to create as clear of a path between them. I’m sure many people here are much more knowledgeable on this subject than I am. Feel free to add to how many FARS a radio can reach.

Two thumbs up! The Red Engineering (RE) Simplex Repeater (SRPT-03) has been discussed in another post. This review is about the new piece of equipment by Red Engineering. Thay have taken a SRPT-03 with all the connectors and placed it inside a polycarbonate waterproof case with a custom made precision-molded ABS insert and foam liner along with a waterproof SNA connector for connecting an external antenna. This is somewhat similar to what RE showed on their website with the original simplex repeater where they put everything inside a Pelican M40 Micro Case. It required that the end-user drill and install a bulkhead SMA fitting for the antenna and any foam insert they wanted. The primary issue with this setup was the size of the M40 case required that the Baofeng UV5 use the small 1,800 mAh battery which really can't go a full 2 day period. The FieldLink Edge uses an Evergreen 56 Waterproof Dry Box Protective Case which allows for the use of the twice as large 3,600 mAh battery with USB connector for charging. The reason for buying a premade case from RE is that the simplex audio and antenna connectors are sized perfectly for the case and both the radio and simplex repeater fit tight and snug into the insert. It even has a velcro strap to hold the radio to the insert. It comes with a right angle SMA connector for the outside antenna which mandates that the case be in the horizontal position. I simply replaced that with a male to male SMA connector so I can put the case up a tree in the vertical position. I'm also getting a male SMA to BNC connector to make the use of the outside antenna easier. Unlike the M40 case this one easily accepts a small carbineer and or small dia. rope to the case. You can also buy an additional mount so the case can be secured to a wall, antenna mount or whatever and be removable. The case is not really made to accept usb c power (not enough room). If that is your requirement then it might be better to get something like a Pelican 1150 and make all the connections yourself. This case is for someone who wants a well-made, ready to go waterproof case where all they bring is something like a Baofeng BF F8HP and hook it up to use over a two day period. Just remember to push the little micro switch next to the right of the USB-c connector to initiate the repeater.

Have a new GMRS Pro (fixed antenna) and it does have a working GPS chip in it that does not require connection to the cellphone through the app. I have not figured out how the GPS is programmed to interface with the radio as it takes about 5 minutes to acquire a GPS position when first turned on with no connection to the cellphone app. Yes, I'm aware of the need for GPS units to download the almanac but for most GPS units the updated almanac is stored and only needs refreshing if one travels over 500 miles from the last acquisition and/or over 6 months since the last time it was used. Here's another weird part. It will immediately show a GPS location when it is connected to the phone app even if that occurs within the first 5 minutes including startup. What I still need to determine is if it updates itself within the first 5 minutes of use. This was shown on the first Track I made on the maps page of the app. It showed the initial location (very accurate) and then didn't update for about 5 minutes. After that it updated itself reliably and the recorded Track was right on. It means you need to turn it on and wait for 5 minutes or so before using the GPS functions. Not sure if the app also sends the cellphone's GPS information to the radio as they would both give you similar results. BTech is obviously confused about how it works. The frequency of updating is variable, sometime every second and sometimes it takes 30 secs or so (all of this implies that it is not using the cellphone's GPS, kexcept possibly a first initial value). Not sure if it is looking for a certain amount of distance moved or what. If you want to see what is happening go to the GPS Status page and watch when the data changes and/or the time stamp for the Last Fix acquired. So, while the radio does have a working and accurate GPS chip, the software could definitely be improved.