CWF-001 Active CW Filter

Vectronics CW Filter Kit with 1W Audio Amp

Phase-Shifting CW Filter by Radio Society of Great Britain


HI-PER Audio Filter: 200 Hz wide; centered at 700 Hz Gausian active filter
with minimal group ringing... I have used this filter for over a decade
and it is very good with qrq cw. It is to be placed just before the final audio amp.
Please see the attached PDF file for the full article about it.

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see eHAM reviews of this filter HERE


This is one of the best external Audio filters with a very clean amp and lots of excellent features:
notch filter
cw regeneration
variable bandpass

see PDF file for full article

PASSIVE CW FILTER KIT from Xtal Set Society, Inc

This filter was easy to build from a kit, and has a very effective bandpass design for cw.
Please click on the attchment WAVE FILE to hear this filter in action.




Here is a spectrum view of the bandpass of this filter for 700 hertz center frequency

Here is the view of the waveform sweep in AUDACITY

Here is what it sounds like sending cw dits from 300 hertz to 1200 hertz

Here is an audio example of how well the HI-PER-MITE filters a harsh square wave sidetone

Here is a very good W3NQN, passive, "GAUSSIAN" designed - cw audio bandpass filter - specifically designed for QRQ CW by W3NQN himself -The Gaussian design is used to preserve the integrity of the shape and sound of the cw that you don't get ringing, or echoing, or that tunnel sea-shell kind of sound etc...or warping of the shape of the cw edges...

Chebyshev and Butterworth cw audio bandpass passive filters usually do not have the ideal passband phase response for copying QRQ CW....they tend to add "coloration" to the cw notes and can even cause ringing and other audio artifacts....However, this unique W3NQN passive cw audio bandpass filter prototype uses a GAUSSIAN FILTER calculation for its inductors and capacitors...the Gaussian bandpass filter does preserve how the CW is supposed to "sound" - it does not color the "shape" of the cw note....

this video...demos the effectiveness of the filter by:

1. listening to a 40 meter cw qso on a web sdr rig.... the filter is bypassed to show how much qrm/qrn the filter is capable of reducing...

2. another test is a spectrum sweep, using a tone generator, a spectrum analyzer will store the sweep and show how well the filter tunes out the frequencies above and below the center(700 hertz) design bandpass frequency...

3. FLdigi is used at 120 wpm to show how well this W3NQN GAUSSIAN filter preserves the shape and sound of the original FLdigi tone... THE green wave on TOP is the original FLdigi wave, the RED wave on the bottom of the scope is the FLdigi tone AFTER it goes through the W3NQN GAUSSIAN cw audio bandpass filter...

4. then a textfile is sent by FLdigi at 120 wpm so you can hear how well the filter keeps the original sound of the FLdigi CW audio intact at qrq cw speeds...the filter does not add echo, ringing, or allow any altering of the shape of the original FLdigi cw notes...

here are the design blueprints on this project by W3NQN:

if you are interested in learning more about this filter, please contact W3NQN about this Gaussian Filter prototype

Here is a specialized use of the typical 3-way speaker crossover to help get rid of the constant high pitch hiss coming out of most audio outputs of most rigs and audio op amps...especially when you listen to CW with headphones

brief demo of using a RADIO SHACK 3-WAY CROSSOVER NETWORK circuit to reduce the usual high frequency audio hiss you hear in most audio amp, audio outputs...especially with headphones...that high pitched hiss can get on your nerves after operating your rig for a while... this simple 3 WAY CROSSOVER Network, i purchased at RADIO SHACK back in the 90's, works pretty well for getting rid of that unwanted high pitched audio amplifier output hiss, by tapping into the CROSSOVER's low pass network - that usually goes where the bass speaker is supposed to go... reduces drastically the amount of high freq hiss you hear constantly...and yet...not changing the quality of the CW AUDIO TONES you really want to hear

NOTE: also works with SSB to get rid of the RADIO's audio output hiss by using the smaller inductor and less capacitance in a LOW PASS configuration

Here is a short video of what QRQ CW sounds like after being filtered by the W3NQN passive CW AUDIO BANDPASS filter

Here is another custom designed W3NQN passive cw audio bandpass filter - BUTTERWORTH - 600 hertz wide - utilized in this video example for listening to QRQ CW COPY practice cassette tapes, so that if you want to repeat the last word or phrase, or jump hitting the tape deck's REVIEW or CUE button...your ears will not be super blasted by the high pitched squeal from the tape deck going into high speed while the tape head is still engaged...etc...  see video notes below for the 2 page PDF of the custom written design specs that W3NQN drew up for this filter...

when using CUE & REVIEW, while listening to cassette tapes for QRQ CW COPY PRACTICE...hitting the CUE and/or REVIEW can blast your ears with very loud high pitched tones.... this custom designed CW AUDIO FILTER by W3NQN puts a stop to that ...

here is the 2 page PDF file of W3NQN's design papers on this filter

Here is a software CW AUDIO filter setup on LINUX using an array of LOW PASS and HIGH PASS filters 

brief demo of showing multiple LP & HP filters arranged in an array to help with QRQ CW COPY when using an EXPONENTIAL CW ELEMENT edge created by the AD5DZ CW Keyboard engine

Here is a software CW FILTER demoD listening to a CW signal on 40 meter HF

Testing the CALF 5 BAND EQ FILTER for copying receive HF CW
even with the rig's 400 hz wide crystal filter...this CALF 5 BAND EQ cw audio FILTER, helps to knock down even further, the background HF static, hiss and noise

also, the CLI COMMAND LINE VERSION of this CALF 5 BAND EQ FILTER is demoD(dj slider to the right)and compared to the GUI version....

a spec an is also in view to compare what the CALF 5 BAND EQ FILTER GUI says its supposed to be, to what is actually being measured by the SPECan APP

once you have dialed in the CALF 5 BAND EQ FILTER the way you like... on the GUI...then...just punch in the numbers for a command line version of it using Gstreamer - that you can save easily and bring up again... and save some space on the desktop

here is the CLI GSTREAMER COMMAND LINE used to duplicate the CALF 5 BAND EQ FILTER GUI's filter settings:
gst-launch-1.0 -v jackaudiosrc ! calf-sourceforge-net-plugins-eq5 ls-active=1 ls-level=0.015625 ls-freq=283.435 hs-active=1 hs-level=0.015625 hs-freq=1628.13 p1-active=1 p1-freq=305.818 p1-level=0.015625 p2-active=1 p2-level=63 p2-freq=678.284 p2-q=0.5 p3-active=1 p3-level=0.015625 p3-freq=1508.97 ! jackaudiosink buffer-time=10000


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