What is a studio-transmitter link?

A studio-transmitter link (STL) is just that. It is the link between the studio and the transmitter. Let's look at one in action. KWIZ radio is a hip FM station with studios on the top floor of the insurance building downtown. They got a good deal on the space, and they like being downtown 'cause it makes them (and their listeners) feel more connected. Their transmitter is located on top of Mount Fritz, some 20 miles away. The transmitter is up there because real estate is a bit cheaper there, and from that spot it can hit (reach) a lot of territory. And the tower doesn't have to be super tall, either. Besides, there isn't any place downtown to put up an FM broadcast antenna. If the antenna was downtown, it would have to be super tall. And it couldn't get the kind of coverage KWIZ can get with a transmitter located up on a big hill. They want lots of area where their signal can reach out to and arrive at receivers. That translates into lots of listeners and lots of opportunities to sell radio ads and get lots of money for them because the station has lots of coverage/listeners. Dusty Rhodes and Sandy Beach share the mic on the morning show. They draw music from the tracks stored in the memory of the station's music computer. (Who still uses CD's?) When they play a tune, the signal is routed to the input of a microwave transmitter on the roof of the insurance building. The microwave transmitter takes that signal and uses it to modulate the microwave carrier, and then the modulated carrier is sent through amplifiers and finally to a microwave power amplifier. From there, it is sent into a waveguide (or, more probably, a length of heliax cable) and routed to the little microwave dish on that short mast on the roof. The dish is a parabolic reflector, and it may be anything from a foot or two across to half a dozen feet across, depending on the system used and the distance it needs to cover. (A meter in diameter would not be uncommon for something like this.) The microwave signal is then radiated from the feedhorn into the dish. From there it is reflected off the dish and goes where the dish is pointed. The transmitter's dish is pointed at a similar receiver dish up on Mount Fritz. That receiver dish (which is pointed at the transmitter dish) is often mounted on the tower that the FM broadcast antenna sits on. The microwave signal is collected on that second dish and reflected to the focal point to be gathered up by a horn positioned appropriately. There may be a low noise amplifier built right into the horn at the focal point of the receiver's dish. The microwave signal is then demodulated and music track recovered. Then that signal can then be used to modulate the FM transmitter, which is right there. The amplified signal goes out of the FM transmitter and into the transmission line which connects the transmitter to the antenna. The signal is being routed point to point from the studio to the transmitter. And that's the studio-transmitter link (STL) that is common today. AM and FM radio stations and also the TV stations use the links commonly.