IMPROVING RADIO MIC PERFORMANCE: THE RANGE FACTOR
by Edwin J. Somers, CAS

This is the third article in a series of ways to improve your radio mic performance. In previous issues, we discussed how using a high gain antenna with the proper polarization in conjunction with low loss transmission line (coaxial cable) will have a dramatic improvement on range. But what else can you do to maximize range?

The first thing you should think about is keeping a fresh battery in the transmitter. Manufacturers tell us that their transmitters have a 6 to 8 hour battery life, which is very true; however, in most systems, as the battery voltage drops, so does the transmitter power. The range will definitely drop off as the battery gets weak. When you want to maximize the range, change the battery after about an hour. Trying to stretch battery life is false economy, especially if you lose an important scene because of a weak battery.

Some manufacturers make high power transmitters. Typical power for VHF transmitters is 50 milliwatts. In fact, that is the maximum allowed by law. Typical power for UHF transmitters is 100 milliwatts. The maximum allowable power for UHF is 250 milliwatts. Some manufacturers do make 250-milliwatt UHF transmitters that will give you about a
4-dBm boost in signal.

UHF is slightly more efficient, so you will realize an increase in range just by switching away from VHF.

Switching to a diversity receiver will have an 'apparent' increase in range. I say apparent because the primary advantage of diversity receivers is to reduce drop outs; however, the net effect is an increase in usable range (which is the subject of another article).

I have been able to demonstrate a drop in signal (and range) when the transmitter is on one side of the performer and the receiver is on the other, at least with using UHF. This means that the radio signal must pass through the performer's body and is partially absorbed by it. If the transmitter is placed on the performer's back, then place the receiver behind them.

The final suggestion is to keep the transmitter gain adjusted properly. The mic gain adjustment controls the percentage of modulation of the FM radio signal. You want it as high as possible. By law, all transmitters have a limiter circuit to prevent over-deviation and co-channel interference. If you set the mic gain so high that it triggers the limiter, it will sound terrible. It is not designed to sound good. The trick is to adjust the gain so that it just triggers the limiter, and then back off a bit. Under normal conditions, you will not have to adjust it very often, only when you encounter a very loud or very soft-spoken performer. The important thing is to think about it each time you use the transmitter. When you maximize the transmitter gain, you get the best signal-to-noise ratio, which translates into greater range.

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