3
optional CW center frequencies may be internally programmed for older Collins KWM-2
and S-Line equipment.
The DSP-59+ also has 12 RTTY, AMTOR, PACTOR, G-TOR and HF packet bandpass
filters centered at 2210 Hz. One of five optional center frequencies may be internally
programmed for other common operating modes such as European standards or 1600-
1800 Hz. HF packet. The selectable bandwidths of the bandpass filters provide optimum
filtering for 170 Hz. and 200 Hz. shift data signals of various baud rates.
The DSP-59+ has individual linear phase fixed bandpass filters with steep skirts for
SSTV, WEFAX and CLOVER. Since the bandwidths for these modes are fixed, the
filters are primarily QRM filters for adjacent channel signals rather than noise reduction
filters for eliminating random noise. The SSTV filter is a dual passband filter with one
passband centered around the SSTV sync pulse at 1200 Hz, and the other passband
around the varying FM picture tones from 1500-2300 Hz.. WEFAX is similar to SSTV
but has no separate sync pulse so the filter bandpass covers 1500-2300 Hz. The
CLOVER filter has a 500 Hz. bandwidth with a center frequency of 2250 Hz.
RTTY Remodulator
The DSP-59+ has a special data function for RTTY only. After passing through the
optimized RTTY bandpass filter, a precision DSP-based FSK detector in the DSP-59+
demodulates the noisy incoming RTTY tones and uses the recovered digital data to drive a
precision DSP-based AFSK generator. This remodulation process takes place entirely in
the DSP-59+. The precise clean tones from the RTTY AFSK remodulator can feed any
analog multimode controller or TU via the DSP-59+ line audio output. Many analog
RTTY demodulators have difficulty with noisy signals of varying amplitude, but virtually
all of them can adequately demodulate the precise DSP AFSK generator output. The
Tone (or Marker on some units) push-button selects either the remodulator with RTTY
filters or the RTTY filters only.
Automatic Gain Control
The DSP-59+ has switch-selectable automatic gain control to optimize the signal levels
for best filter performance and to enhance listening by minimizing audible signal level
variation.
Test Mode
The DSP-59+ has two test modes: a self-test to verify proper operation of the DSP-59+
circuitry, and a audio signal generator mode to test other equipment. The self-test mode
checks the internal digital and analog circuitry, push-button switches, LED indicators and
connectors. The self-test mode not only verifies the operation of the DSP-59+, but also
aids in verifying the proper installation of the DSP-59+. The audio signal generator
mode produces low-distortion, precision frequency sine wave test signals at the
frequency of each highpass and lowpass filter. Also, the Tone or Marker mode produces
low-distortion, precision frequency sine wave signals at the center frequency of each
bandpass filter. The test signals include single sine waves, two-tone signals for SSB
testing, and mark-space tones for modem testing. These precision tones may be used for
calibration and/or trouble shooting of other equipment the user may own.
