What were sound/vision combiners needed for?
At early TV stations, the vision and sound components were separately recorded and amplified and then had to be properly combined for joint broadcasting via an antenna.
How sound/vision combiners worked
Sound/vision combiners were based on a conventional directional coupler combiner consisting of two 3 dB directional couplers and two dual-circuit band filters tuned to the audio transmission frequencies. The output of the audio transmitter was split by the first directional coupler, routed through the filters, recombined by the second directional coupler, and finally sent to the antenna. The output of the image transmitter was also divided by the second directional coupler, reflected to the filters, then recombined and routed to the antenna. The vision and sound transmitters were therefore uncoupled from one another. The filter bandwidth was variable, permitting both dual-sound operation and NICAM (the acronym for “near instantaneous companded audio multiplex”) tuning.
Over the years, SPINNER repeatedly improved the design of its sound/vision combiners to keep pace with technical advances. In 1973 this gave rise to the first 40/4 kW sound/vision combiner, and in 1979 to the first 10/1 kW sound/vision combiner for the 4.5 band. These were followed in 1993 by a redesign of the 10/1 kW and 20/2 kW sound/vision combiners. Full compatibility with the older models was retained, with identical coordinates for the RF connections and the possibility of installing them in 19” racks.
In 2005, finally, a 5/0.5 kW sound/vision combiner was introduced for the IV/V band. SPINNER developed this compact version in response to the growing demand for sound/vision combiners for power levels up to 5 kW. In conjunction with new state-of-the-art manufacturing technologies, the company succeeded in introducing a completely new product to the market. This combiner and its data naturally also matched the excellent radio-frequency values of the more powerful models.
When analog television was superseded by digital technology, sound/vision combiners were no longer needed. Today, audio and video signals are generated together and compressed (for example, as an MPEG), and then the result is amplified.