TB9400 Installation and Operation Manual Installation 75© Tait Limited March 20174.6.5 Connecting RFNotice Do not remove the load from the PA while it is transmittingas this may damage the PA output stage. Before disconnecting any RFcables, put the base station into Offline mode to prevent any transmis-sions.The RF input to the base station is via the marked BNC connector on therear panel of the reciter. The RF output is via the N-type connector on therear panel of the PA (refer to Figure 4.9 on page 71).Cables and antennas should be of high quality construction. Solid shieldheliax type cables are best, but if braided shield cables must be used forshort distances, their braids must be silver-plated.Recommendationsfor Installing the PA We recommend the following installation procedures, which should protectthe PA from damage under all but the most extreme operating conditions.1. Do not connect the PA directly to the antenna. Fit an isolator orduplexer between the PA and the load. Fit the isolator as close as pos-sible to the RF output connector on the PA. Do not connect anyswitching equipment between the isolator and the PA, unless theswitch cannot operate while there is RF present (i.e. the base stationis transmitting).2. Fit a surge suppressor to the antenna cabling where it enters thebuilding.3. Inspect all cables and equipment connected to the base station fordefects.Ice on the antenna, or a broken antenna, is unlikely to cause damage to thePA.Explanation The circuit design of the PA protects the circuitry from high VSWR. Thismakes it difficult to damage the RF power device by keying the PA into amismatched load, or if the load deteriorates over even a short period of time(milliseconds).However, it is possible to damage the device if all the following conditionshappen at the same time:■ there is a step change in the PA load (for example, the load is removed)■ the PA is transmitting■ the feed line loss between the PA and the mismatch is <1dB.The effect of such conditions is variable: some devices will not bedestroyed, and some may fail after repeated load interruptions.
