On Mon, 2009-08-31 at 22:28 -0700, Jim Brown K9YC wrote:
> On Mon, 31 Aug 2009 19:57:58 -0600, Dr. Gerald N. Johnson wrote:
> >The HIFI phones give out lots of lows and highs that don't help
> >separate weak signals from noise.
> "Give out" is a prejudicial phrase. Modern headphones are full range
> and low distortion.
Yes it is and was intended.
> That generally IMPROVES intelligibility rather
> than hurting it. Besides -- by their nature, modern ham rigs have
> VERY limited frequency response, thanks to their extensive bandwidth
> filtering, whether with crystals or DSP. Ten Tec has traditionally
> been very good at tailoring the audio response of their radios.
Not so all over. Most rigs have audio responses from 20 or 30 Hz to 20
or more KHz using HIFI audio output chips without band limiting. Then
all the post filter amplifiers have much greater bandwidth than the
filters and ALL that amplifier noise ends up in the head phones or
speaker. And that is ignoring the wide spectrum artifacts from a DSP
working at audio. I use a passive low pass filter on my rigs to limit
that post IF filter noise. If I start using the headphones I bought,
I'll probably have to use that filter too. Then some rigs like the IC
746 my club likes for FD like to have a LF rumble from envelope
detecting nearby SSB signals to the point that the last time I tried
that with headphones, that I kept lifting the headphones to see how
close the train was, even though we were more than a mile from the
nearest train tracks. Having a narrower pass band in the audio and
headphones would not have given out those annoying none signal
components. There is no need for audio stage or reproducer responses in
ham gear down to 30 Hz or above 3 or 4 KHz yet with wide range head
phones that wide response is present.
> Jim Brown K9YC
73, Jerry, K0CQ
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