About community radio

Because of this post, I have received some e-mail asking why I am against community radio.  I am not.  In fact, I support community radio.  I think that community radio done well is a wonderful tool in our democracy, giving a voice to those that are watching government.  It also promotes other locals interests, events, music, etc.    I would like to see more failing stations bought by community broadcasters and turned into something that is a public trust and responsive to the local population.

What I was trying to get at in the previous post was that over crowding the FM band with more and more small signals will degrade it.  There is no ifs, ands or buts, removing third adjacent protections on the FM band will increase the noise floor.  This will lead to more interference on the average FM radio, which will lead to more people getting fed up and tuning out.

Here is why:  You cannot change the laws of physics.  FM transmitters have output filters that attenuate side band energy, that is to say, energy transmitted on 1st, 2nd and 3rd adjacent channels.  A 50,000 watt FM station on 100.3 MHz will have side band energy on 100.1, 99.9 and 99.7 MHz as well as 100.5, 100.7 and 100.9 MHz.  Due to the limitations on the components used to construct those filters, they can only be designed with the accuracy of the components used.  In other words, most electrical components have a tolerance given in percent, example +/- 10%.  That means that the value of the component will change, usually because of heating.  Therefore, output filters cannot be constructed to limit emissions to only the main channel and say one adjacent channel, they would drift off frequency.

Also, creating a brick wall filter that cuts everything off at the second adjacent channel will cause distortion of the RF signal on the main channel.  With analog AM and FM transmitters it cannot be done.  Digital transmissions are another story, but that is not what we are talking about here.

That is an engineer’s point of view.

One other thing about adding hundreds more LP FM signals.  There should be something that stipulates most (say >50%) of the programming be locally originated.  Recorded for later playback is fine.  Having thousands of LP stations broadcasting the same syndicated shows or running voice tracked automation 24/7 would be a recreation of the AM band as it currently exists.  If you want to listen to that, then it already exists, help your self.  I, on the other hand, would like to avoid the AMization of the FM band.

That is all.

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