Variable Bandwidth Filter Modules SSB/CW

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Variable Audio Filter Module

NEW Dennis KG4RUL has developed an Arduino sketch for our Vari-filter; this includes a nice display. Download the sketch here and a PDF circuit diagram here. It utilizes a SODIAL USB Nano V3.0 ATmega328 16M 5V Micro-controller CH340G board, or similar, available from Amazon and other sources and an OLED display module such as the HiLetgo 1.3" IIC I2C Serial 128x64 SSH1106 OLED LCD Display LCD Module for Arduino AVR PIC, or similar. Dennis is happy to share this but cannot offer any support - so please do not contact him.

NEW Magazine review - Practical Wireless, used with permission.

Our LASERBEAM-VARI digital variable audio filter module is the perfect addition to your project or even to your existing radio. Unlike analogue filters, digital filters provide near-perfect characteristics. Because of the way that they are implemented, they are better than analogue filters in almost every way!



LASERBEAM-VARI Modules been designed for ease of use. One simple control allows you to continuously vary the bandwidth or the centre frequency of the filter. All settings produce the same great filters with flat passbands and steep skirts. Whether you need passband tuning, filters for digital modes and APRS, low pass filters or CW filters, the LASERBEAM-VARI does it all in one compact module. Dial up EXACTLY the filter you need.

  • Bandwidth 200Hz - 3500Hz
  • Max Passband 200Hz - 3500Hz
  • Indicator outputs for tuning mode (bandwidth or centre-frequency)
  • On board overload indicator
  • User-defined power-up filter settings
  • Two gain settings

Great for all modes: SSB-CW-Digi-AM-NBFM.

A single clickable rotary encoder provides the main functionality. Click to switch between variable bandwidth or centre frequency. Store your favourite setting as a power-up default. Simple but very effective. The filters are continuously variable and always have near perfect characteristics unattainable with conventional analogue techniques.

Kit includes:

  • filter module PCB (ready-built),
  • Bourns rotary encoder (6mm diameter shaft) ,
  • 3 x LEDs,
  • 2 x 10 way headers,
  • 7 resistors, 2 capacitors.

Simple to use: the instructions are downloadable here. The instructions contain information to allow users to control the filter using a microcontroller.

Example filters

These plots have been made by testing a LASERBEAM-VARI using a professional audio spectrum analyser (QuantAsylum QA400). Remember that the LASERBEAM-VARI can synthesise any bandpass filter that you want (200-3500Hz). Click on the links below to see the filters.

Using your LASERBEAM-VARI module

The most common question I get is "can I fit your filters inside xxx type of radio?". The answer is generally yes.

LASERBEAM-VARI modules are ready-built and easy-to-use. Make a few connections and you will soon be good to go.

In most radios they can be fitted before the volume control. You may need to adjust levels. The only control you need to bring to the front panel is the rotary encoder although the mode LEDs are very useful. In essence, some ingenuity is needed to retro-fit VARI-BEAM filters. The effort is worth it though, as it really can make old receivers sound quite spectacular.

IMPORTANT NOTE: The LASERBEAM-VARI module is not suitable for use with our BOXA-DUAL filter enclosure kit 


Also available from our international agent(s): 



LASERBEAM-VARI modules have been designed to be easy to use. Connections are kept to the minimum:

  • DC power
  • Rotary encoder
  • Audio in (single ended)
  • Audio out (singled ended or differential)
  • Optional Mode LEDs (2) 
  • Optional Off-board Overload LED
  • Optional Gain switch (Voltage gain 1 or 4)

An LED on the module lights if the input level is too high making it easy to set up your filter. The audio input is protected on the PCB so you can't easily damage it!

The filter module will drive high-sensitivity (e.g. > 110 dB SPL/mW) earbuds directly. For higher outputs a simple audio amplifier such as an LM380N could be added. LASERBEAM-VARI modules are Altoids-friendly!

The modules are perfect for use in existing radios or an an outboard filter. We used one with a Rockmite and the difference was simply amazing! These filters are also great with the popular PIXIE transceiver.

LASERBEAM-VARI Module Specification

Supply voltage: 5 - 15 Volts (reverse polarity protected)

Typical supply current: 50 mA @ 12 Volts

Filter type: multi-tap FIR (KBD Window)

Phase response: linear

Module size: 36 x 36 mm (approx 1.4 x 1.4 inches)

Weight: 5.5 grams

Voltage gain: 1 or 4 (selectable)

Ultimate rejection: better than 60 dB

Passband ripple: <0.15 dB

Input impedance: 8000 Ohms

Output impedance: 750 Ohms

Output type: differential (can be used single-ended)

Maximum AF input Voltage: 2.4 V pk-pk (input protected)

Minimum AF input Voltage: 300 mV pk-pk (recommended)

Maximum AF output Voltage: 2.4 V pk-pk

Processing delay: 22 mS

What is the difference between a LASERBEAM-VARI filter and a standard IF crystal/mechanical filter?

Characteristic VARI-BEAM FILTER IF Crystal/mechanical filter
Cost Low High
Bandwidth options Fully variable 1 per filter
Within AGC loop? No Yes
Shape factor Excellent Average
Ultimate rejection >60dB > 50dB (but usually well away from filter bandwidth)
Filter gain Yes - if required Typically 6dB loss
Residual noise Yes - low level No
Requires power Yes No

10 Reviews Hide Reviews Show Reviews

  • 5
    Audio filtering doesn't get better than this.

    Posted by Rick JI1HSV on 9th Aug 2016

    I originally purchased the CW filter with the intent of comparing it to my variable SCAF filter but before I could build the unit SOTABEAMS released their VARI filter so I got one and started building a dual channel DSP filter with audio amps. (Sent the CW filter for re-progamming, different review)

    I was certainly not disappointed, this filter REALLY works. It is a bit subtle though, there is none of the ringing or super peaking you would find in other types of audio filters, adjacent signals just disappear!

    Initial setup of the VARI filter can be a bit confusing as both center frequency and band width are variable. I used a IPad app called 'SignalScope' where I can see a FFT of the audio. I first set the center frequency to the side tone of transceiver, switch to bandwidth mode and push the 'default'. I then set the
    bandwidth and pushed the switch again.

    You have to be creative in mounting the filter as there are no holes on the board and smd parts are mounted very close to the edge. I inverted the 10 pin header pins and then these plug into a perf board that has 10 pin female headers. This
    allows mounting the LED and encoder resistors under the DSP filter on the perf board.

    I use two of the VARI filters followed by 2 watt audio amps and some mini relays for bypassing everything for AM SWL operation.

    I would definitely recommend using a DC source of no more than 9VDC. There is no reason to unduly stress the little 3.3VDC SMD regulator on the DSP board.

    Bottom line...
    Cost/Performance is excellent. Service from SOTABEAMS is excellent.

    If anyone has any questions my call is on