Tait TB7300 Installation And Operation Manual

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Tait TB7300 Installation And Operation Manual Manual pdf 64 page image

64 Installation TB7300 Installation and Operation Manual© Tait Limited November 20165.6.3 Connecting RFNotice Do not remove the load from the base station while it is trans-mitting as this may damage the PA output stage. Before disconnectingany RF cables, put the base station into Offline mode to prevent anytransmissions.The RF input to the base station is via the marked BNC connector on therear panel. The RF output is via the N-type connector on the rear panel(refer to Figure 5.4 on page 62).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 theBase StationWe recommend the following installation procedures, which should protectthe PA from damage under all but the most extreme operating conditions.1. Do not connect the base station directly to the antenna. Fit an isolatoror duplexer between the base station and the load. Fit the isolator asclose as possible to the RF output connector on the base station. Donot connect any switching equipment between the isolator and thebase station, unless the switch cannot operate while there is RF pres-ent (i.e. the base station is 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.