The Truth About Operating Range
Overview
In this article we will consider only the typical types of wireless equipment that are used in the short-range control of moving firearms targets. There are two sets of laws that limit the performance of these wireless remote control systems. These are Federal Law as implemented by the Federal Communications Commission and the Laws of Physics.
The Federal Communications Commission (FCC) enforces laws controlling which parts of the radio spectrum can be used for various purposes and what type of transmissions are allowed in those parts of the spectrum. To implement its responsibilities the FCC tests and certifies radio transmission equipment. It is important to understand that the certification responsibility of the FCC is NOT to ensure that a certain piece of equipment operates in the way it is designed to do or in the way that the manufacturer advertises it to perform. The FCC is only interested that the equipment will operate within the FCC's own established parameters. These parameters usually include a maximum permitted output power, a restriction on signal patterns and that the equipment will not cause undue unwanted interference to other nearby electronic equipment operations.
The "Laws of Physics" take over where the responsibility of the FCC ends. The FCC ensures that the transmission characteristics of a piece of equipment do not exceed certain limits. The Laws of Physics then further restrict the performance of that equipment.
Why do we say "restricts", can the performance not "improve"? The answer is "No" or at least "very unlikely". The reason is that when the FCC certifies a piece of equipment the tests are carried out under near perfect transmissions conditions. The FCC wants to limit the MAXIMUM power output of a transmitter so it tests under the best possible transmission conditions. By definition, when we try to operate the same equipment under real world conditions we are going to see less than the performance achieved under the test conditions.
Factors Restricting the Performance of Wireless Remote Control Systems
Note the careful choice of words in the heading above.
There are factors that "RESTRICT" the performance of wireless systems. The implication is that the systems would perform better without certain restrictions. There is not much we can do to avoid the legal restrictions. However, we can reduce some of the physical restrictions.
We are considering the overall "PERFORMANCE" of the system not just considering the output power of the transmitter (which is the factor that gets most attention). Performance includes such factors as tolerance to interference from other transmitters and the system's reliability.
We are considering "SYSTEMS". A reliable wireless link is the total of the contributions of the transmitter, receiver and the antennas - not solely the transmitter.
Improving System Performance
Surprisingly, with one major exception, the one factor we can forget about almost immediately is the power output of the transmitter. A very rough indication of the power output of a transmitter is the number of watts of power the transmitter produces. The maximum permitted power output of a cell-phone in the US is three watts. The maximum power outputs permitted by the FCC for the transmitters we are considering are a fraction of a watt. You can see we are not allowed to generate much power and this amount of power can easily be reached by the electronics inside the transmitter case. Therefore we can say that nearly every remote control transmitter can, potentially, generate the maximum FCC permitted power output. The question then becomes, can that generated power output be converted into a strong usable radio signal outside of the transmitter case? This depends on the efficiency of the transmitter antenna which leads us to our major exception mentioned above, transmitters with inefficient antennas.
The best size for a transmission antenna depends upon the frequency at which it is to operate. As an example, at 418 Mhz., a popular remote control frequency, for high performance an antenna should be approximately 6 1/2 inches long (this is a complicated subject so excuse me if I simplify). If the equipment designer wishes to use a transmitter case that is 3 inches by 2 inches (the approximate size of a cell-phone) then obviously an optimum size antenna is not going to fit. Using a reduced size antenna will reduce the amount of power generated by the transmitter electronics that can be sent into space. In the worst case this may mean that a transmitter is, in fact, unable to radiate the amount of power permitted by the FCC.
So what can we do to procure a wireless system that meets our performance needs?
Assuming we have a transmitter that works to its maximum permitted efficiency what really matters is the ability of the RECEIVER to detect our signal at the low power levels we are using and turn it into usable information. One of our problems is a law of physics known as the " inverse square law". To put it simply a radio signal does not lose its strength with distance as we would expect. A quick estimation would suggest a radio signal's strength would reduce by half every time we doubled our distance from the transmitter. Unfortunately this is not correct. The signal strength reduces as the inverse square of the distance. To give an example, if we move from fifty yards away from a transmitter to one hundred yards away from a transmitter we would, at first, expect the signal strength to fall to ONE HALF of its original value. In actual fact, the signal strength falls to ONE QUARTER of its original value. You can see now why we get into trouble so quickly as we move away from our transmitter especially since it did not have much power to start with. So how do we deal with our performance problem?
The first, and cheapest, attempt at a solution we can look at is to change the location of the transmitter and receiver. At the power levels and frequencies we are considering the equipment needs as much help as it can get. Position the transmitter and receiver as close together as you practically can (remember the inverse square law). Ensure that there is a clear signal path between the transmitter and receiver antennas. If you still have a problem then on to the next step.
The second least expensive solution is to consider the quality of the transmitter and receiver antennas. We cannot do much about the transmitter antenna because, when the FCC certified the transmitter, it did so with a certain antenna. It would almost certainly be illegal to change the transmitter antenna without having the transmitter re-certified by the FCC. However, the transmitter signal pattern may not be uniform in all directions. It may be that you could get improved signals by holding the transmitter in a certain position relative to the receiver. Similarly, orienting the receiver differently may improve the reception. Fortunately, the FCC does not put the same strict restrictions on changing the receiver antenna that it puts on changing the transmitter antenna. A more efficient receiver antenna is an option but it must be remembered that the antenna needs to be matched to the receiver. Selecting the wrong antenna may make performance problems worse rather than better.
If you are still not getting satisfactory performance it may be possible to get a more sensitive receiver (of course, the new receiver must be designed to work with the rest of the system). It appears that this would receive the weak signal better and that is true. Unfortunately another problem rears its ugly head. Our transmitter is almost certainly not the only one, intentionally or otherwise, operating on our chosen frequency (the interfering transmitter could be another radio transmitter or even an old car with bad ignition). We have got a sensitive receiver and this allows us to increase the distance between the receiver and the transmitter. It also means we are probably receiving the signals from another transmitter operating on the same frequency more strongly. If our luck is bad, at some point, our receiver is going to get confused. All the receiver knows is that it has to receive a signal on its selected frequency - it does not know WHICH signal. So now our receiver becomes a great receiver for somebody else's signal. Down goes our remote control link.
It almost looks as though there is nothing else we can do. We are using maximum transmitter power, the most efficient antenna and the most sensitive practical receiver and still our control signals are not reliable. Don't give up. Now we have to start getting clever. Do you remember the story about someone hearing their name mentioned across the room by someone else during a noisy party? Despite all the noise and confusion going on in a room, for some reason, a person seems to be able to recognize their own name when it is spoken. We can use the same trick with a radio signal. We tell the receiver to hear its name spoken in a noisy radio crowd. This trick is performed in various ways, it may be with the way the signal is transmitted, it may be with the way the transmitted information is arranged. Some of these methods are of limited effectiveness but they are adequate for their purpose. Others are very effective and often are expensive to implement. The problem, of course, is that this is not a technique that can be applied by the user. It has to be built into the transmitter and receiver during manufacture or programming. This is the technique used by ShootingPartner,
Conclusion
So what does all this background material have to do with the original web page name "The Truth About Operating Range"? It really boils down to a few considerations.
First, the operating range claimed in advertising is probably optimistic, it will be a "best possible" value. (I bet you are really surprised!). Find out whether the seller will guarantee performance at that range.
Second, the claimed operating range and the reliable performance range may be two different values. For example, two wireless systems may have similar performance under ideal conditions but one of the systems may be far superior when the conditions are more difficult due to that system having greater technical sophistication.
Third, consider that price is not always a good indicator of performance. With advances in electronics and associated reductions in production costs a modern lower price system could easily outperform an older system that is more expensive to produce.
Fourth, if high performance is required it is probably wise to stay away from systems that use very small "garage door opener" type transmitters. These transmitters do not have the space inside the case for the type of antenna that is required for high performance operation. Even when the antenna is mounted outside the case it is usually too small for maximum efficiency. As we have seen, efficient antennas are necessary for performance at the very low power levels we are considering.
Fifth, buy your system from someone with practical knowledge of wireless remote control. It may be that knowing how the equipment REALLY works and how to install it for best results on your range is as important as buying the most expensive equipment.
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