If multiple antennae and feedlines are possible, an installation with separate transmit and receive antennae provides increased performance.

No duplexer is required. Instead high quality pass/notch cavity filters protect the receiver from interference. The pass/notch filter on the receiver input is tuned to "pass" the receive frequency and "notch" (or reject) the transmitter output frequency.

The pass/notch filter on the transmitter output is tuned to "pass" the transmit frequency and "notch" (or reject) sideband noise from the transmitter on its output at the receive frequency. High quality pass/notch filters available from several manufacturers. Bandpass only filters are generally not acceptable.

Antenna placement and type is critical. The antennas should be mounted on a tower in such a manner that the receive antenna is directly above the transmit antenna with as much vertical separation as is practical, but no less than about 5 wavelengths. Vertical separation can provide 40 dB or more antenna to antenna isolation. With the filter configuration as shown above, more than 100 dB transmit to receive isolation is generally achievable. Since all cavity type filters are temperature sensitive, the smaller number of filters provides better performance at extreme premerature swings than with duplexer- based installations.

Typically exposed dipole array antennas provide better performance than vertical colinear "stick" antennas.

The tuning of the pass notch cavity filters and antenna placement should be such that less than 0.5 dB de-sense is measurable in the receiver. This can be verified by connecting a communications analyzer or service monitor, such as an Agilent (HP) 8920 or an IFR-COM120B, to the antenna port and injecting an unmodulated signal at -100 dBm on the repeater receive frequency. The receive signal strength is displayed on the front panel of the base station repeater, in dBm. When the base station transmitter is keyed, the RSSI display on the base station repeater should not decrease or increase. Typically the base station receiver can successfully decode mobile signals down to about 0.5 microvolts (-112 dBm) with zero frame errors.

If the base station repeater's second receiver is employed for diversity operation, a second antenna and feedline and an additional pass/notch filter is required.