On Sun, 2009-04-05 at 21:43 -0500, Bob McGraw - K4TAX wrote:
> Ken makes some good points.
> I have owned 2 different Omni VI Plus radios, both equipped with a tummy
> full of filters. And there's been a Paragon II and a couple of original
> Paragon's across the desk. Those are purely analog audio.
> One fact that can contribute to audio fatigue has largely to do with the
> speaker used with the radio be it internal or external. I won't name names
> or brands or types, but some are good and some not so good for voice and CW
> work. As a general rule, I've found that a "hi-fi" type speaker connected
> to most ham radios will produce lots of unwanted noises. Those become
> fatiguing as unwanted noises are just unwanted energy that the ears and
> brain are required to eliminate. The result is hearing fatigue.
Hi-Fi headphones are even worse because they often have wider responses
than ordinary Hi fi speakers. Especially lows that expose the rumbles of
IC-746 in the presence of nearby SSB signals. There was a lot to be said
for the headphones from WW2 with a 1 KHz resonance to make it easier for
pilots to hear beacon station IDs. I clean up speaker high frequency
noise with a switchable passive low pass filter. I need to make that
circuit into a web page some day. Its been in use decades. It needs a
couple 70 volt line to voice coil transformers to keep inductor and
capacitor sizes reasonable and uses the primary taps to allow using the
same inductors to achieve several cutoff frequencies. CW sounds really
clean with the tone set for 400 Hz and a 450 Hz 7 pole Tchebychev low
pass filter. Almost no noise. For me, too little noise!
73, Jerry, K0CQ
> Bob, K4TAX
TenTec mailing list