[Kenwood] Question re: 950sd / 950 sdx and 850 w/dsp100

[John Tait]

> Broadening the Transmitter AF response wastes power.
> Any additional sidebands so generated fall outside the response curve of
the receiver into the big black hole, (probably somebody
> trying to work alongside you).
>
> If it ain't broke don't fix it.

I agree Gary..

 If Tom W8JI will forgive me, I think a quote from one of his previous mails
is very relevant...

..." 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!  "


   I think he "says it all " in that quote..
   73
   John EI7BA  http://www.iol.ie/~bravo/