[1000mp] Audio choice- Not HiFi

[Tom Rauch]

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