Perhaps many US listeners would be surprised to learn that the AM broadcast stations they listen to limit their bandwidth to 5 or 6 kHz for several reasons.
In many tests listeners prefer the reduced bandwidth because it improves the AM signal/noise ratio when signals become marginal. They never miss the highs because the most common AM radios today - car radios - have filters that limit their audio bandwidth to less than 5 kHz! Broadcasters have discovered they can "sell" the un-needed bandwidth they are entitled to use for non-listener functions, so they have a double incentive to limit the broadcast bandwidth. Here's a couple of on-line resources for the curious: http://www.rwonline.com/article/1672 This report notes: "These objective measurements established that the majority of current analog AM receivers have audio bandwidths of less than 5 kHz. In fact, with only a few exceptions, the frequency response of individual receivers falls off above 1 or 2 kHz. As shown in Fig. 1, the combined frequency response of all receivers through the test bed (the middle curve, in blue) was -3 dB at 2450 Hz and -10 dB at 4100 Hz. Another interesting report is here: http://findarticles.com/p/articles/mi_m0EIN/is_2007_Feb_2/ai_n17166612 I suppose the moral is that bandwidth is like money: It's not how much you have but what you do with it that counts in the end. Ron AC7AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
