NoiseOFF V1.0 Audio DSP Filter For Sale -

This small DSP filter improves the reception of SWreceivers. The board provides twofilters for SSB (normal and narrow),one filter for CW and a noisereduction algorithm. The filter must be inserted into the audio path betweenthe output of the receiver and an external active speaker or headphones.

Table 1: TypicalCharacteristics

Filter Type

Bandwidth [Hz]

Comments

SSB Normal

250 - 2300

At -3db, linear phase, 0.1 db ripple

SSB Narrow

250 - 1800

At -3db, linear phase, 0.1 db ripple

CW

300

Centered on 750 Hz, linear phase

Denoiser

-

Adjustable in four steps, 6 – 36 dB

Thefilter must be powered from a voltage source between 4.2V and 15V and thetypical current consumption is 55mA.Refer to Figure 1 for details about the connections. The board is protectedagainst the input voltage polarity reversal but the user must avoid thissituation.

There are two jack-type connectors (3.5 mm) on board,one for input and one for output. The input signal should not exceed the amplitudeof 1.5Vpp. Use the volume button ofthe receiver to adjust the signal in order to avoid possible distortions. Thegain of the DSP filter is set to 0 dB (one), so the input signal is notamplified. The input impedance of this filter is set to 32 ohms. Use the headphones output of the receiver to provides theinput signal. The output can drive an active speaker or a pair of sensitive headphones.The minimum impedance of these headphones is 32 ohms

Table 2: Typicalinput/output parameters

Parameter

Value

Input voltage range

4.2 – 15 V

Current consumption

55 mA typ.

Input signal amplitude

Max. 1.5 Vpp

Input impedance

32 ohms typ.

Load impedance

Min. 32 ohms

TheSW1 push-button controls theband-pass filters (SSB and CW) each push changing the filter type. The sequenceis: SSBNormal àSSB Narrow àCW à No Filter.The default power-up state of the filter is “No Filter”. The LED1 lit when one of the band-passfilters is active. There is no indication about the type of filter but theeffect on the audio bandwidth is noticeable.

TheSW2 push-button controls the denoiser(Noise ReductionAlgorithm) each push changing the “aggressiveness” of the NRalgorithm. The sequence is: NR on àNR+ àNR++ àNR+++ àNR off. The LED2 lit when the NR algorithm is active. There is noindication about the level of the NR algorithm but the effect on theaudio is noticeable.

The board can be placed into a small box. Use the jackconnectors screws for fasten the board. The mechanical dimensions are depictedin Figure 2. Some external push-buttons (normally open) must be connected inparallel with the existing onboard buttons. Use small pieces of isolated wiresfor this operation.

This board is not intended to be placed inside the receiver. Avoid anymodifications of the receiver circuitry in order to avoid any possible damages.

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