With the soon-to-be flurry of HD Radio FM power increases kicking in nationwide, we’ve heard there could be a problem in some markets – especially those where the transmitter sites have many stations using one combiner. Examples could be NYC on the Empire State Building and Miami on the old Omni America Tower. In some cases upping the transmitter power on 8-10 FMs may just be too much for the existing combiner system to handle. We’ve heard that some broadcasters are racing to increase their power without considering that it might prohibit other broadcasters sharing that site from doing so. We invite comment on this issue and do suggest that a coordinated approach be made between broadcasters at these sites before the increases are put into play. Replacing a combiner system can be quite expensive as we all know. It is also difficult to maintain the over-the-air signal while changing out the combiner.
Commented Greater Media VP/Engineering Milford Smith: “Although we (Greater Media) don’t operate in NYC, I was made aware of a possible issue with the Empire combiner. Transmission systems vary significantly from station to station and from one multiple user site to the next. It would seem that this would potentially be an issue where stations are either using low level combining (and thus inputting the analogue and digital signals simultaneously to an existing analogue combiner) or are back feeding an existing combiner which, in either case, was operating pretty close to maximum ratings before any attempt was made to increase digital power. In other situations separate analogue and digital combiners are sometimes used for transmission and it is also a possibility that a digital combiner sized for a nominal -20 dBc by the multiplexed stations might possibly not be adequate for the task if the combined stations increased digital power to -14 dBc or better. We are seeing this possibility at several sites where we operate in other markets. Keep in mind that a change from -20 dBc to -14 dBc is a four times power increase while an increase to -10 dBc is a ten times increase. Those are very significant numbers when dealing with the sizing of RF components.”