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control. 20 kHz first I-F filer + 455 kHz I-F
filter + DSP BW filter at the third I-F should
be adequate under most circumstances to
keep the receiver linear and maintain the
ability to hear weak signals in the presence
of multiple loud ones.
FACTORS THAT AFFECT THE
SOUND OF SSB TRANSMIT
AUDIO AND THEIR ADJUSTMENT
One of the features of the OMNI-VII is
flexibility afforded the operator for the
desired sound of SSB transmit audio.
Many possible settings are available so that
operators with different styles (or
philosophies) can adjust the radio the way
they want it to sound. Obviously, the
operator who favors rich, full-sounding
transmit audio is not going to have the same
needs as the DXer who wants maximum
"oomph" to try and break a SSB pileup.
There are several controls that interact on
OMNI-VII for SSB transmit audio. Every
operator is different; we use different
microphones, the timbre of voices are
different, distance from the microphone will
vary. What we intend below is to describe
what is used to tailor transmit SSB audio,
and then encourage the operator to
experiment with the settings to find the
sound they want.
A monitor function has been provided for the
operator to listen to the sound of actual
transmitted SSB audio. We recommend
using headphones while using the monitor
circuit to prevent microphone/speaker
feedback. See the description of (25)
MIC/MON.
There are five radio controls used for SSB
transmit audio. 1) Transmit bandwidth,
which is adjusted using the SSB TX BW
control in the menu. 2) Low frequency
rolloff, adjusted with the TX ROLL OFF
control in the menu. 3) TX EQUALIZER,
adjusted via the menu. 4) Mic gain,
adjusted via the front panel MIC/MON
button. 5) Speech processing, adjusted via
the front panel SP/VOX button.
Additionally, there is a hardware mic gain
588 manual
Part #74409
Printed in USA
control that is accessible under the front of
the bottom panel.
Transmit bandwidth is both the frequency
response of the transmitted signal and the
amount of spectrum occupied by that signal.
Typical communications-grade audio for
SSB is in the 2.4 to 2.7 kHz range. Some
"hi-fi" SSB enthusiasts have been
experimenting with larger transmit
bandwidths in an effort to improve the
quality of audio transmitted. OMNI-VII has
been provided with the ability to transmit on
SSB with a maximum bandwidth of 4000 Hz.
Please see the note toward the end of this
section about wide SSB transmit bandwidths
and their potential ramifications.
Set SSB TX BW in the menu to an
appropriate value based on your operating
preferences. For communications-grade
audio, we recommend starting the transmit
bandwidth at 2400 Hz. For more well-
rounded transmit audio, start the transmit
bandwidth at 3.0 kHz (3000 Hz). The
default value is 2700 Hz.
The next control to adjust is TX ROLL OFF,
also found in the menu. TX ROLL OFF
refers to "low frequency rolloff". This control
interacts with SSB TX BW determine your
frequency response.
For example, if SSB TX BW set to 3000 Hz,
and TX ROLL OFF is set to 200 Hz, the
response envelope for your transmitted SSB
signal is approximately a low of 200 Hz and
a high of 3200 Hz for a total bandwidth of
3000 Hz. Using the same 3000 Hz SSB TX
BW setting, if the TX ROLL OFF s changed
to 100 Hz, the response envelope is now a
low of 100 Hz to a high of 3100 Hz, for a
total bandwidth of 3000 Hz. You can think
of the TX ROLL OFF control as where the
"bass response" from your voice and the
transmit bandwidth is attenuated.
OMNI-VII is equipped with a transmit
equalizer, labeled TX EQUALIZER in the
menu. The TX EQUALIZER establishes a
specific audio profile for your transmitted
audio from either the MIC or line input
sources (see description of AUDIO
SOURCE and LINE GAIN in the menu).
The TX EQUALIZER is a 6 dB/octave filter
selectable in 1-dB steps from high pitched at
–20 to essentially flat response at to 0 dB to
very bassy at +20 dB.
Second release – August 2007
30
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