9
Use the PTTI bypass in the voice mode to prevent unwanted transmit audio from the transceiver
from causing audible interference. Many transceivers do not mute their audio outputs
completely during transmit. The 36 dB extra gain from the DSP-59+ with the AGC on makes
the incompletely muted transmit audio audible and may even cause oscillation by acoustic
feedback from the speaker to the microphone.
A contact closure operates the PTTI circuit. No external power is required. The return (shield)
side of the PTTI jack is connected to the DSP-59+ circuit and chassis ground.
Some linear amplifiers have 115 volt supplies for their transmit-receive relays. If a transceiver
PTT line is used to drive both the DSP-59+ and an linear amplifier, an isolation relay
and/or isolation diode may be required to prevent damage to the DSP-59+ (and any other
solid state equipment connected to the PTT line).
5. Operation
Introduction
Three knobs and five push-button switches on the front panel control the DSP-59+. Eight
internal jumpers located on the circuit board near the back panel preset options for some of the
front panel controls. One knob controls power and sets the speaker and headphone audio output
level of the DSP-59+. The other two knobs select the filter and test generator frequencies of the
DSP-59+, and control random noise reduction aggressiveness. The push-buttons select the
operating modes of the DSP-59+. Note that depressing a push-button always selects the mode
indicated below the push-button. Also note that if the Bypass push-button is depressed, other
controls will have no effect on the operation of the DSP-59+.
Power Switch/Gain Adjust Control
The gain knob on the front panel of the DSP-59+ is the power switch/gain adjust control. Rotate
the gain control clockwise to turn on the DSP-59+ and increase the volume. Rotate the gain
control counter-clockwise to turn off the DSP-59+ and decrease the volume. Turning off or
removing power from the DSP-59+ automatically de-energizes a bypass relay and forces the
DSP-59+ into the bypass mode.
5.1 Voice and Wideband Data - Highpass/Lowpass
In HP/LP mode, the DSP-59+ conditions the audio response of the DSP-59+ using a
combination of highpass filters and lowpass filters, adaptively reduces random noise, and
adaptively eliminates multi-tone noise (heterodynes). These three functions can operate
simultaneously or independently as outlined below.
To activate the highpass/lowpass filter mode, place the red HP/LP push-button in the out
position. Turn the High Pass control to the desired frequency indicated by the blue numbers
around the High Pass control. Turn the Low Pass control to the desired frequency indicated by
the blue numbers around the Low Pass control. These two settings customize the frequency
response of the DSP-59+.
