The DB-1000 Base Station Repeater requires an antenna system which employs suitable external filters. Receiver de-sense by the transmitter is not desirable, and consequently high quality filtering is necessary. For a typical one channel system, a four cavity pass-notch duplexer and on additional pass notch cavity filter is recommended. In most UHF systems, the base station repeater transmits on a frequency five megahertz below its receive frequency. A transmit-receive pair of frequencies is referred to as a "channel" or "channel pair". The mobile and portable field units transmit on the reversed pair.

The duplexer and additional cavity filter combination should provide at minimum 100 dB Transmit to Receive isolation. It should be tuned to provide minimum loss to the antenna for both the transmitter port and frequency and the receiver port and frequency. Maximum transmitter to antenna loss should be kept to 1.0 dB or less. The notch filtering is adjusted to minimize the transmitter fundamental at the receiver port as well as sideband noise on the receive frequency in order to prevent receiver "desenging" when the transmitter is on. The pass/notch cavity filter should provide more than 25 dB loss at the notch (transmit) frequency, less than 0.5 dB loss at the "pass" (receive) frequency.

Pass-pass types of duplexers are not acceptable. The duplexer must be at minimum a four cavity unit of a type with "notch" adjusting capacitors on each cavity. Typically two notch adjustments minimize sideband noise from the transmitter directly on the receiver frequency, and two notch adjustments minimize the transmitter fundamental to the receiver. Six cavity duplexers of similar design may be used however generally they exhibit additional power loss to the transmitter.

The tuning of the duplexer and pass notch cavity filters 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 0.25 microvolts (-118 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.

The "IM Panel" (Intermodulation Protection Devices) typically consists of a single or dual circulator, and an optional low pass filter. It is not required when the repeater is installed at a location without any other nearby transmitters, but is highly recommended. It prevents signals from nearby transmitters from being received by the antenna and conducted to the transmitter output stage, where heterodyne mixing can occur, causing "intermodulation" interference.

High quality double shielded 50 ohm coaxial cable or 100% shielded coaxial cable is mandatory. Typical filter interconnect cabling may be RG-400, Andrews 1/4 inch "Superflex", or LMR-400 or 600. Do not use connector to connector adapters but only the appropriate type of N or BNC connector. Because N and BNC connectore are available in 50 ohm and 75 ohm versions, ensure that 50 ohm connectors are utilized.

A well-grounded lightning arrestor, such as a "Polyphaser", is recommended on the antenna transmission line. The repeater and all of the filter components should be properly installed in a grounded equipment rack or cabinet.