[Elecraft] K3 filter widths re: speech intelligibility

[Chuck Murcko]

The definitive paper on noise, bandwidth and their relationships in a  
communications channel is still Claude Shannon's 1948 paper "A  
Mathematical Theory of Communication":

http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html

It's the signal to noise ratio in the channel that will determine if  
a given voice bandwidth will get through, and how much of the power  
in that bandwidth will actually be useful to communicate information.  
It's also why DXers tend to favor narrower TX bandwidths, since they  
tend to operate in marginal S/N conditions.

Most modern USAF fixed station radios use 2.8 kHz as a default  
bandwidth (at least all the Motorola MiComm II we use).

The PolyComm article is based on a noiseless channel, BTW, so it is  
not surprising that it concludes that the wider bandwidths are best  
for intelligibility. Unfortunately, this is not the case on HF comm  
channels much of the time due to fading, interference, and noise.

73,
Chuck KE3KR

<begin quoted mail>

Interesting, although I have to take into account the fact that the
publisher of the report has a vested interest in showing that more
bandwidth is appreciably better for voice communication.

73, doug


    Date: Fri, 29 Jun 2007 15:09:34 -0400
    From: "DOUGLAS ZWIEBEL" <dougzzz at gmail.com>

    http://www.polycom.com/common/documents/whitepapers/ 
effect_of_bandwidth_on_speech_intelligibility_2.pdf

    Don't confuse single single intelligibility of speech (and  
especially
    speech quality) with speech intelligibility during heavy band qrm.
    It's always a balancing act.

    Argh.  This is why I have forgotten "the phone" and concentrate  
on cw.

    de Doug KR2Q

<end quoted mail>