Discontinued Product

DSP-9+ Noise Filter

Simultaneously reduces noise, kills heterodynes and filters QRM!

Reduce noise and interference
- Adaptive noise filter for SSB and AM
Eliminate heterodynes
- Automatic multiple tone noise filter
- AGC (Automatic Gain Control)
Sharp Speech, CW and Data filters
- Linear phase FIR filters
- 1.6, 2.0 and 2.4 kHz. Bandpass
- 100, 200 and 500 Hz. Bandpass
Built-in Self-Test
The DSP-9+ uses digital signal processing technology to provide optimum filters for random
noise reduction, heterodyne elimination and bandpass filtering. Digital Signal Processing (DSP)
technology provides superior performance in reducing QRM and QRN.
No other technology can do what DSP can!

New Version 3 Features

Remodulator for RTTY, New noise reduction algorithm.
Improved data filters and more!


The noise reduction functions of the DSP-9+ operate by examining a characteristic of signals and noise called correlation, and dynamically filtering out the undesired noise. The degree of correlation is relative. Random noise such as white noise or static is uncorrelated. Speech is moderately correlated. Heterodynes and pure tones are highly correlated. The DSP-9+ measures correlation and automatically filters out noise that is outside its correlation thresholds. The amount of noise reduction varies according to the correlation characteristics of the noise. Typical noise reduction ranges from 5 dB to 20 dB for random noise and up to 50 dB for heterodynes.


Narrow band signals like CW and RTTY require bandpass filters with steep skirts and linear phase response. Linear phase response maximizes the usable signaling rate for a given bandwidth and minimizes ringing often heard on other types of extremely sharp filters. The filter skirts on the 195 CW filters are so steep that a signal literally falls off the edge of the passband as you tune through a CW signal. Bandwidths range from 25 Hz to 600 Hz, and center frequencies from 400 to 1000 Hz. The narrow filters are useful for trying to dig out extremely weak signals from the noise and QRM. The wider filters allow easy tuning and listening to multiple CW signals simultaneously. The selectable bandwidths of the 2210 Hz and optional data bandpass filters allow selection of the optimum bandwidth for 170 Hz and 200 Hz shift data signals of various baud rates.


Front panel pushbutton switches enable quick, independent selection of all the functions on the DSP-9+. In the voice mode, the operator can simultaneously select a bandpass filter, the tone notch filter and the random noise reduction filter. This means you can reduce QRN, filter adjacent-channel QRM, and eliminate heterodynes at the same time! In the CW mode, simultaneous selection of both the random noise reduction filter and a bandpass filter reduces background hiss as well as adjacent-channel signals. AGC (Automatic Gain Control) is selectable in all modes to optimize filter performance and listening ease with varying signal levels.


The DSP-9+ is compatible with all amateur radio transceivers and receivers. Simply connect the DSP-9+ between the radio and its speaker or headphones. Connect 12-16 VDC to the DSP-9+ and turn it on!



Impedance 2K ohms or 22 Ohms, jumper selectable


Output power 1.6 watts into 8 ohms at 13.8 VDC, 2.5 watts into 4 ohms at 13.8 VDC
Line output level -6 dB, referenced to input level, into 10K ohms. Not controlled by gain control
Distortion less than 1% at rated output


Function Frequency range Attenuation Type Delay
Random Noise Reduction Entire range of
selected bandpass filter
Up ro 20 dB, varies
with noise characteristics
Adaptive 5 msec max
Tone Noise Reduction
(multiple automatic notch)
Entire freq. range of
selected bandpass filter
Up to 50 dB, varies with
noise characteristics
Adaptive 5 msec max
Bandpass - Voice 300 Hz - 3.4 kHz, 300 Hz - 2.7 kHz
and 300 Hz - 2.1 kHz
or (jumper selectable)
300 Hz - 2.7 kHz, 300 Hz - 2.3 kHz
and 300 Hz - 1.9 kHz
60 dB at 180 Hz
outside the passband
FIR Linear
10 msec max
Note: The Random Noise Reduction, Tone Notch and voice Bandpass filters can operate simultaneously.


Function Frequency range Attenuation Type Delay
Bandpass - CW Bandwidth = 100 Hz,
200 Hz and 500 Hz
Center freq. = 400, 500,
600, 800 Hz (select any two by
internal jumper, or Collins
KWM-2 mode with center
freq. = 1350 and 1500 Hz
60 dB at 50 Hz
outside the passband
FIR Linear
30 msec max
Random Noise
Entire freq. range of
selected bandpass filter
Up to 20 dB, varies
with noise characteristics
Adaptive 18 msec max
Note: The random noise reduction and CW bandpass filters can operate simultaneously.


Function Frequency range Attenuation Type Delay
RTTY Bandwidth=250 Hz. 55 dB at 50 Hz
outside of bandpass
FIR Linear
18 msec max
AMTOR Bandwidth = 340 Hz
PACTOR, G-TOR Bandwidth = 440 Hz
HF Packet Bandwidth = 540 Hz
All Data Modes Mark - Space freq. pairs = 2125 - 2295,
2110 - 2230, 2025 - 2225, 1615 - 1785,
1600 - 1800, 1430 - 1630, 1275 - 1445,
1260 - 1460, 1215 - 1385, 1200 - 1400 Hz
Jumper table in Manual
Note: All Data filters and Random Noise Reduction can operate simultaneously


Front Panel
Volume / Power On-Off Voice / CW bandpass Bandwidth
switches (wide and narrow)
Voice / CW / Data Mode
switch and LED indicators
CW center frequency switch
(high and low)
Bypass switch Overload LED
AGC switch Normal LED
Random Noise Reduction switch RTTY, AMTOR, PACTOR,
and HF Packet switches
Tone Noise Reduction switch RTTY Remodulator switch
Rear Panel
Audio Input Phono jack - RCA style
Speaker Audio Output Phono jack - RCA style
Line Audio Output Phono jack - RCA style
PTT Input Phono jack - RCA style
Power In 5.5 mm / 2.1 mm power
jack (center positive)


A-D/D-A Converter 16 bit linear, sigma-delta conversion
Signal Processor 16 bit, 77ns Analog Devices ADSP-2105


Self-test Self-test for circuitry, switches, and PTT input. User initiated from front panel.


Size 5.9 in. wide x 6.7 in. deep x 1.9 in. high (150 mm wide x 170 mm deep x 48 mm high)
Weight 2.0 lb. (0.9 Kg.)


12-16 VDC @ 1A

Amateur Products

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