Power Focus
Time and again I see techs use the “high power” setting on any transmitter that happens to have one. But with RF, we usually don’t benefit from having more power than needed.
All that’s needed is enough. It’s analogous to digital audio in that going over the maximum input level (0 dBFS) does not do anything positive, just harsh clipping and overloading.
What more power does get us is more intermod products and more desensitized antennas, which leads to more interference and drop-outs as well as more reasons to think more power is needed to make the system work.
In my experience, the only time the high power setting on a transmitter is needed is when it’s known for sure that the transmitter is going to be a long distance from the antennas. An example is an anthem mic set up in the middle of a football field.
Figure 3 shows the before and after effects of having a Telex BTR-800 base station at “high” and “low” (“norm”) power. Note the red lines showing the intermod products.
Note also that this is from a unit that has been modified to have separate antenna outputs for Tx-A and Tx-B, and that these have in turn been put through an antenna combiner (which suppresses some of the IM products). A stock unit would generate much more IM in the high power mode, and more than what is shown here in the normal power mode.
Nothing To Gain
The same holds true for antenna gain, which exists solely to overcome signal losses in cables. Using higher gain on an antenna does not help to “pull” Tx signal out of the air. What it does do is make the antenna more sensitive to everything, including off-air DTV and low-level intermod products generated by the normal interaction between wireless transmitters. In other words, it raises the noise floor.
To avoid having to use excess antenna gain, utilize quality cable (this is a whole separate topic), keep cable runs as short as possible, and use a cable loss calculator to determine exactly how much gain is needed and then choose the closest gain setting on the antenna.
In summation:
1) Improper handling and placement of transmitters can generate a considerable amount of IM products and raise the overall noise floor. This wastes precious bandwidth.
2) Antenna placement, especially in respect to orientation of Rx and Tx antennas, is critical for successful outcomes.
3) High Tx power and high Rx gain settings are not helpful unless the specific situation absolutely calls for one or both.
Ike Zimbel has worked in pro audio for 35-plus years, and during that time he has served as a wireless technician and coordinator, live engineer, studio technician, audio supervisor for TV broadcasts, and has also managed manufacturing and production companies. He runs Zimbel Audio Productions (zimbelaudio.com) in Toronto, specializing in wireless frequency coordination and equipment repair/modifications.