[1000mp] Audio choice- Not HiFi

[1000mp@mailman.qth.net]

How about speech processing, does that increase the duty cycle and 
stress the pa and ps componets also.  I think in AM the power is 
reduced to 25 watts for the MP if my memory serves me.  I don't use 
AM and I might add that some of the dirtiest signals I have EVER 
heard are on AM.

Dale
K9VUJ





>I use HiFi headphones and speakers, but I do tailor audio
>response of receivers when necessary to eliminate hiss. But the
>comment below strikes a nerve with me!
>
>>  Under strong signal conditions, AM signals on large wider frequency
>>  range speakers can seem to be nicer and thus the way to always go for
>>  listening under all conditions, and that is simply not true of course.
>>  Some using the legally questionable wide 6khz sideband, and pushing
>>  low frequency audio trying to emulate AM audio quality, are actually a
>>  step backwards for what Ssb communications is all about... ...which is
>>  improving range and intelligibility using less power than the same AM
>>  signal (AM as in double sideband with carrier, of course single side
>>  band is also AM) AND less band space.
>
>It isn't just the HF response that causes bandwidth problems with
>transmitters, it is the low frequency energy content. PA stages and
>power supplies are bad enough when amplifying normal SSB
>signal. Add a lot of bass, and dynamic regulation of voltages in non-
>class A PA stages becomes even worse.
>
>Generally the dynamic regulation of the supplies (including bias
>supplies) is quite lacking in almost all solid-state rigs. That's one of
>the reasons radios have such poor transmitter IMD performance in
>two-tone tests. The other is output and driver devices are often
>marginal on headroom.
>
>By the way, two-tone tests are poor ways to measure IMD....it is
>actually almost always worse than a two-tone test
>indicates...because low frequency content isn't mixed in. I use
>three-tone IMD tests when I test PA's, with a low-frequency tone
>varied between syllabic and bass (300Hz or so) frequencies.  
>
>I see people turning the internal power limit pots inside radios up
>just like CB'ers do, getting maybe 130-150 watts out of a FT-
>1000MP. The "splatter" of course is many times worse than
>normal. This is becoming more popular, and is a somewhat popular
>MP mod.
>
>Some obviously think because the radio CAN do 150 watts it
>SHOULD be OK at 150 watts (or whatever). They forget (or never
>knew) many or most transistors get very non-linear even at 2/3 of
>maximum power.
>
>The other issue is heavy bass in audio, which of course bias and
>Vcc supplies have the hardest time dealing with. Small electrolytic 
>capacitors can not help hold the voltage steady. Not only that, the
>exaggerated bass wastes energy and robs the PA of headroom to
>handle high frequency energy. The result is greatly increased IMD
>levels (splatter).
>
>As a general rule, even if the stations restrict HF audio response,
>HiFi audio stations (while they feel good about how they sound to
>their HiFi buddies) are MUCH wider than "regular" audio stations.
>While some of this is due to extending high frequency response,
>much of it is because they crank in so much bass.
>
>The exaggerated bass response taxes regulation of supplies and
>removes headroom for sharp peaks.
>
>The power limit thing mostly seems to be something going around
>in contesting circles.
>
>Run these problems into some of the new tetrode PA's with poor
>IM performance and you are really asking for bandwidth problems!
>
>73, Tom W8JI
>W8JI@contesting.com
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