[AMRadio] Suggestions Please

[Donald Chester]

>From: "Jeff Edmonson" <w5omr at w5omr.shacknet.nu>

>...but, running a rig, with an audio response of 50hZ to 5kHz?  Where
>does the "excessive" line stop?

When band conditions (congestion) don't permit it.  When the band is 
crowded, I find receiving bandwidth greater than 6 kc/s unuseable.  Under 
congested condx, audio beyond 3.5 kc/s will probably not be heard anyway, so 
argument can be made that it should not be transmitted, since it only wastes 
spectrum space.  But under less crowded condx, if you can reasonably expect 
to be able to open your rx bandwidth to 8-10 kc/s, the extra audio can make 
a difference, and there is prenty of room in the band for other stations to 
operate besides 2-3 kc/s away from at AM carrier.  That's why I have the 
choice of two low-pass audio filters in my rig.  On 10m. I often run with no 
filter.

On the low end, the human voice goes down to about 100 cps or below.  The 
voice sounds more natural when these frequencies are present, but it can be 
counterproductive to boost them to generate "jukebox" sound. Just keep the 
transmitter response flat and use a good microphone. If bass frequencies are 
transmitted, they must be balanced by the highs, or else the signal will 
sound bassy and will be unintelligible under noisy/QRM condx. I balance my 
bass by using a pre-emphasis curve beginning at 800 cps and reaching about 
10 dB at 2000 cps and above.  I then sharply cut off the highs above 3400 
cps, or gradually cut them off above 5000 cps, selecting the appropriate 
passive L-C filter.

Don K4KYV

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