[AMRadio] 32V-2 speech amp question


Grant Youngman nq5t at comcast.net
Mon Jan 23 16:14:08 EST 2006


> This seems counterproductive to me.  Why expend time and money on a 
> transmitter that can pass down to 10 cycles up to 15 Kc and 
> then restrict 
> it?  Why not build one that will go down to 200 and up to 8.  
> Frequencies 
> below 200 Cy do not contribute to the information transmitted 
> and rob from 
> frequencies that do.  

There's a general rule that for best perceived or most natural voice
quality, the low frequency cutoff times the high frequency cutoff (in cps)
should be about 500,000.  Obviously, both the transmit and receive end have
an impact on this.  

If we assume a wide bandwidth receiver with good (flat) response, then a
transmitter with a 5000 kc high end cutoff should have about a 100 cps low
end.  Or a transmitter that can handle 10 kcps on the high end should go
down to 50 cps on the low end.  Let's say it does that.  Let's say my R390
is limiting high frequencies to 2 Kc because I am center tuned at 4 kc
bandwidth because of nearby SSB.  The perception I'll have of this beautiful
transmit signal will be that it is all bass -- no articulation, and really
hard to understand (confirmed by a lot of listening to weak "east coast
sound" signals from 20V's or whatever).  

Even a 4 Kc high end transmitted with 50 Hz low end could sound bassy
(depending on whether I'm an "accouncer" voice or a squeaker, no matter how
the receive bandwidth is set.  I usually run with about 150 Hz low freq
cutoff, but then I'm a squeaker, and going much below that won't help :-)

So I have to agree with you.  If the guy on the 20V is "full quieting", and
you can run your receive bandwidth wide open, then enjoy what there is to
hear.  Most of the time, it's just too much bandwidth (which doesn't mean we
ought to be prohibited from doing that if conditions are right AND it can be
done without causing undue interference).

Grant/NQ5T 





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