[Elecraft] AM receive band width

[Ron D'Eau Claire]

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