Tait TB7300 Installation And Operation Manual

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Tait TB7300 Installation And Operation Manual Manual pdf 53 page image

TB7300 Installation and Operation Manual Installation 53© Tait Limited November 20175.6.3 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 disconnectingRF cables, put the base station into ‘Offline’ mode to prevent any trans-missions.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 51).Cables and antennas should be of high quality. Solid shield heliax typecables are best, but if braided shield cables must be used for short 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 conditions1. Do not connect the base station directly to the antenna. Fit an isola-tor or duplexer between the base station and the load. Fit the isolatoras close as possible to the RF output connector on the base station.Do not connect any switching equipment between the isolator andthe base station, unless the switch cannot operate while there is RFpresent (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.A broken antenna or ice is unlikely to cause damage to the PA.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 <1dBThe effect of such conditions is variable: some devices will not bedestroyed, and some may fail after repeated load interruptions.