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[TenTec] Re Microphones--one more thing (long)

To: <tentec@contesting.com>
Subject: [TenTec] Re Microphones--one more thing (long)
From: tjednacz@ieee.org (Thomas Jednacz)
Date: Wed, 15 Jan 2003 16:05:07 -0500
Hello all:

Sorry to jump in and spoil your fun. DO NOT change the carrier offset. You
will then be transmitting on both upper and lower sideband!! Filter rigs are
set at 300 Hz cut off so the filter slope will will get you -30 dB on the
other sideband. If you change the offset the filter will not have a steep
enough slope to drop the other sideband to the required level. Filter rigs
are not adaptable to less than 300 Hz audio without creating problems. I
have looked at the fellows on 178 and find that they are using up to 40 dB
boost (over normal audio levels) at 100 Hz and driving the audio and or A/D
converter in the DSP chip crazy. They say their RF stages are all linear.
True - BUT they generate all kinds of junk in the audio stages by driving
them non-linear and transmit 12 - 15 KC wide signals when they only intend
to transmitt 4Khz. A full DSP rig (Pegasus/Jupitor, Icom 746 Pro/756Pro,
Kachina, and of course the new Orion) are the only ones that will properly
transmit 100Hz to 4 Khz audio and be clean.

Play with equalizers and all the other audio stuff but don't try to make a
system design do what it is not supposed to do. Do not consider HI-FI/SSB
with anything but a full DSP radio as above.

When playing with HI-FI/SSB lets understand what we are doing, use good
engineering practices and have some courtesy in sharing frequencies with our
fellow hams.

Tom, W7QF


-----Original Message-----
From: tentec-admin@contesting.com [mailto:tentec-admin@contesting.com]On
Behalf Of Barry N1EU
Sent: Wednesday, January 15, 2003 3:29 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Re Microphones--one more thing (long)


--- Mark Erbaugh <mark@microenh.com> wrote:
> Could you share with us how you run a response curve
> and how you determine
> the needed EQ. I would like to do some analysis work
> on my GoldLine / W2IHY
> 8 band Eq / Pegasus setup.

Mark, a full treatment of your question would take a
long time.  I'll make a few comments off the top of my
head with the disclaimer that there are guys right
here on this reflector who know more than me.  I've
been hacking at it for a few years though.

The best way to judge mic equalization is with your
own and other folks' experienced ears.  On a
hifi-capable receiver, listen to a lot of ssb signals
closely for what you do and don't like about their
sound.  Listen to the guys on 14178 and on the TT net,
and you'll hear some really good and not-so-good
sounding audio.  By hifi-capable, I mean a minimum of
2.8khz bandwith with carrier offset aligned properly
to extend bass response to below 100hz.

Run your receiver audio (line level) into your
soundcard and get some recording and spectral analysis
software.  There's some freeware/shareware out there
(just search around), but currently I'm using CoolEdit
Pro for recording and SpectraPlus for spectral
analysis.  Record WAV files of those signals that you
do and don't like.  You can open the WAV files in
SpectraPlus and it will show their response curves
after running a spectral analysis on them.  After
doing this many times, you can correlate what your
ears are telling you and what the computer is telling
you.  I'm sure there are lower cost alternatives to
SpectraPlus, but you'll have to look around.

For setting your own EQ, you can record yourself off a
second hifi-capable receiver while transmitting
(choose a phrase with a few sentences and keep using
it as your standard) and get a good idea of what you
sound like as well as run a spectral analysis on it.
Solicit many opinions from others on the air who can
listen critically as you adjust the audio.

There are a few links on my Web site under "Audio" to
NU9N, KC4PE, W3OZ, etc. where there's a wealth of
information and different perspectives on getting the
equalization correct.  There's also a ssb-audio
reflector on Yahoo Groups.

GL/73,

Barry N1EU
http://www.albany.net/~bg





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