[Elecraft] AM receive band width

[Erik N Basilier]

Very interesting Ron!

This suggests that the radios where AM broadcast sounds good (portable 
radios and car radios) have built-in
bass suppression and/or treble emphasis for AM, which supports the need to 
use the equalizer on the K3.
Since the K3 is primarily for amateur communications, and many amateurs have 
microphones that emphasize
the highs, it makes sense for the K3 to rely on the equalizer rather than 
impose a non-flat response on all.
(However, it helps make the case for eventually getting mode-specific 
equalization on the K3.)

When it comes to the living-room stereo that sounds lousy on AM I guess 
spec-manship prevents the
manufacturer from counteracting the broadcasters' roll-off, lest the 
expensive box look non-flat on paper.

73,
Erik K7TV

----- Original Message ----- 
From: "Ron D'Eau Claire" <ron at cobi.biz>
To: <Elecraft at mailman.qth.net>
Sent: Sunday, February 01, 2009 2:55 PM
Subject: Re: [Elecraft] AM receive band width


> 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
>
>
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