Shure - Products

Remote Antennas for UHF Wireless Microphones

Antennas are measured in terms of the wavelength of the signal that they are designed to pick up. The standard antenna supplied with Shure UHF wireless systems is a "1/2-wave", meaning that it is 1/2 of the length of the radio wave being received.

For good performance, the following guidelines should be observed when remote mounting antennas

Place antennas properly. Antennas should be mounted away from large metal objects or surfaces, which cause reflections that can reduce signal strength. Antennas should also be kept away from sources of RF energy, such as computers, digital devices, AC power equipment, etc. For best diversity performance, antennas should by placed from 1/2-wavelength to 1 full wavelength apart (1 to 2 feet for UHF). Wider separation between antennas does not offer significant benefit, except when mounting at opposite sides of a very large stage, for example. For diversity wireless systems, both antennas must be located in the performance area, and connected to the receiver via separate coaxial cables.
Use the appropriate antenna cable. For proper performance, the impedance of the cable should match the impedance of the antenna input on the receiver (50 ohms for Shure receivers). An impedance mismatch causes some of the signal to be reflected back into the cable, resulting in a reduction of signal level. Different types of cable are rated according to the amount of signal loss over a specified length (usually 100 feet). These ratings are specific to the frequency range of the signal being passed (VHF or UHF). The maximum length of cable is dictated by how much the antenna amplifier can boost the signal. See the section on antenna amplifiers. It is not necessary for both antennas on a diversity receiver to be connected to identical lengths of cable; ideally, each antenna should be connected to the minimum length of cable necessary to reach the receiver. The following table describes the maximum length of cable that should be used between a UHF antenna and a receiver input. If antenna boosters are used, the cable length can be usually be longer depending on how much gain the booster provides. For example, using a booster that provides 10dB of gain, and following the cable loses specified on the table, you could run 69 feet of RG58C/U or 108 feet of RG8X/U.

UHF Antenna Cable Loss Over 100 Feet?
Cable Length from Antenna to Receiver	Cable Type	Cable Loss @ 800 MHz per 100 feet
Up to 15 feet	RG-58C/U(Belden 8262 or similar)	18.5 dB per 100 ft.
Up to 25 feet	RG-8X/U(Belden 9258 or similar)	12 dB per 100 ft.
Up to 40 feet	RG-213/U (Belden 8267 or similar)	7 dB per 100 ft.
Up to 75 feet	RG-8/U(Belden 9913 or similar) for permanent installation only	3.9 dB per 100 ft.

Minimize the number of connection points. Each connection between two sections of cable results in some additional signal loss. Use one continuous length of cable to go from the antenna to the receiver. If antenna amplifiers are being used, mount the antenna directly on the input of the first amplifier, use one length of cable to go from the amplifier to the a second antenna amplifier (if needed), and from the second antenna amplifier to the receiver.

Use an antenna amplifier to compensate for cable losses. For long cable runs, an antenna amplifier such as the UA830A can be used at the antenna to boost signal level. Up to two UA830A's may be used (one located at the antenna, and one in the middle of the cable run) permitting total cable runs of up to 500 feet when the appropriate type of coaxial cable is used. If a cable run longer than 500 feet is called for, it is better to locate the entire receiver closer to the performance area, and run a long audio cable to the mixing console. A long audio cable (balanced and line level) is much less likely to pick up interference than a long antenna cable. (Note: the UC4 receiver does not supply DC power to operate the UA830A or UA870.)

No more than two UA830A antenna amplifiers can be used in one antenna line. This restriction is due to increasing noise due to the amount of gain been added to the signal, and to the limited amount of current that the U4 receiver or UA840/UA845 antenna distribution amplifier can supply at their antenna inputs. This current is used to power the UA830A, eliminating the need for a separate power supply.