A local radio station transmitter

A local radio station reported that their transmitter was suffering with low output, with alarm lights on, indicating a bad SWR reading. This is normally where the antenna is badly matched to the transmitter, causing a high degree of reflected power.

Upon having the transmitter on the bench, we found that there were several issues. The last problem was that the output stage seemed to be damaged as even with a dummy load matched to the transmitter, power was low and certain parts of the antenna tuning circuit was running hot. Eventually we found that the coax cable from the final power stage to the antenna socket was faulty. This was caused by the original fault with the antenna. The coax link had overheated and became resistive leaky. Amazing the output stage transistors did not fail. A testament to the Broadcast Warehouse design!

With the transmitter now working well, attention turned to the antenna. A Sirio wideband antenna. Very simple in construction. However a design flaw. The outside case which is the main radiator is connected to the RF feed by one small screw. The case is aluminum, the screw is stainless steel, the RF feed made of brass. So, dissimilar metals, RF current and rain cause corrosion. This deal with and all wal well.

This large SBS radio transmitter was being used as a repeater for a station north of Almeria. Output was low and things generally rather sad. Upon inspection, many dry joints around the power supply were found along with failing capacitors. The main issue was that the combiner section, the transmitter having 4 separate power stages, had bad or open circuit connections and damaged components. Not the easiest of machines to work on. Eventually all sorted.

Staging the new transmitter for an upgrade to Smooth FM radio station here is Spain. The existing 500Watt ELENOS transmitter will be refurbished and installed a s a repeater elsewhere. The new transmitter, a PCS Cybermax 1000 Watt should provide a litte extra coverage, filling some of the dead spots.

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