PA3CLQ's Leuke Linken Nr. 453

Resonant CW Speaker

The resonant CW Speaker is featured in the February 2017 issue of QST.

A simple and inexpensive thing to build, and the author said that after listening to CW with the Resonant CW Speaker, a regular speaker will be unacceptable. That hook got me, and I built one.

The author is absolutely right!

It performs better than an active audio filter!

I love this little thing!

One of the best gadgets I've ever added to my shack.

The price tag for parts is minimal, under $15, and an hour to build using a Dremel tool and a soldering iron.

I have a loss of hearing and set the CW tone to 600 HZ so to get the speaker to resonate that low I added 2" PVC coupling between the speaker base and the street elbow, and just turned the elbow around.

I used two 1/8" mono jacks instead of the author's RCA jacks since my radio takes the 1/8" mono plug for the external speaker output.

Works like a dream!

I recommend you should give it a try, I think you'll love it too!



Hello Rich,

Thank you. 
I went out an cut some PVC pipe to start building mine after our QSO.

I hope, my build of the "CW speaker" will make a great addition to my 2B.
72/73 and TU, Jeff K9JP


That was the Skytec product of the '70s.

I have a few...they work very well!


I made something similar, many years ago, with stiff cardboard shipping tubing for 750 Hz notes.

Maybe I will make one next, with the PVC pipe, but maybe several inches longer since I have my radios set for 400 HZ notes.

CW is Real Radio 73, John...K8JD


A few years ago, I built one of these, based on an article in QST... but wanting to do a quick and dirty version first, as a proof of concept, I built it out of a piece of scrap Foam-core, held together with duct tape... with cotton balls around the back side of the speaker.

It worked great, and still sits on my rig....

Good luck with yours.

73 de NC4RT


I'm currently building one.

One thing I did was to get a small sheet of plexiglass (about 6" square) from the local hardware store rather than use CD covers -- it isn't nearly as brittle and is easier to work with.

I'm just waiting for the electronics to arrive so that I can finish it -- hopefully before the weekend.
Andy, k2oo


Its in the February QST.

You can find it at :

and read it if you're a member.
Andy, k2oo


Any speaker will do. 

The magic comes from the cavity.
You tune in a note you like then slide the plunger in or out to peak it.
Or if an interfering tone tune it to notch the un wanted tone too.


Any ideas about making a lower frequency one?

I assume the enclosure would need to be proportionately larger; or can you just use use a longer straight section with the 2" pvc elbow?
73, Drew AF2Z

Yup that's all it takes.

A larger tuned chamber.

BUT also look for the "Natural Resonant" frequency of the speaker.

Choose one that is closest to your freq of choice and it's even more effective.
Every speaker has a natural resonant freq.



Same as a dipole or vertical antenna too, longer for lower freq> It's just physicics.

CW is Real Radio 73, John...K8JD


Try this link...

73, Ed - ad7gr


I guess I should have added the link to K5LN's article:

Dave - W3NP


See attachment pse



This email message is a notification to let you know that a file has been uploaded to the Files area of the skcc group.
File : /Tuned Speaker Calc.xls
Description : Simple spreadsheet to calculate frequency of a tuned speaker when the length and diameter of the tube is known.

see attachment pse



Resonant Speaker: Another Design

What is a resonate CW speaker?



According to the math... Using the formula F=122.4/(L=(0.3*D)) where F is frequency, L is length of the tube and D is diameter of the tube, as you decrease the length of the horn the resonant frequency will increase.

So, if you decrease the length to 5.73" the frequency should be 759 Hz.

If you were to have a length of 5.73" and increased the tube diameter to 2.25" you would have 750.5 Hz. I've uploaded a simple spreadsheet for this to the Files Folder..
73, Ed - ad7gr


If you have a top-firing speaker on your rig, simply buying a 4" PVC elbow and setting it on the speaker produces a resonance in the 650-750 Hz range.

I call this the "Passive Vocal Clarifier" speaker accessory, or "PVC" for short (grin).

If you want to lower the pitch. try setting the elbow on a ring of styrofoam, or just spacers.

To raise the pitch by 50-75 Hz, cut off about 1/2 inch from the lip of the elbow.
Dana Browne AD5VC


I made the speaker (twice!) and got the following results:
1. The frequency response is very narrow. (Good!)
2. The audio output was extremely low -- too low to be of practical value in my shack.
Have others gotten the same results?

Anyone better?

I'd love to improve the results and would welcome any suggestions if they are out there.
73 Andy, k2oo


Sounds like you don't have enough power goint to the speaker.

Did you use headphone output or speaker output to drive it?

Headphone output usually has a resistor in siries inside the rig to keep you from blowing out your eardrums when you use efficient headphones !

Measure the AV volts with a tone going to the speaker, should get good, loud volume with anything over 1 V AC across the speaker. .

CW is Real Radio 73, John...K8JDREM :

Hello Andy,

I had the same results as you.

Where on your radio did you connect the audio input (Audio out of your radio) side of the speaker? 
I have a PROIII and first used the front "phone jack" for my audio input to the resonate speaker.

I also had the very low audio output with my radio volume control turned all the way up.

Then, I took another look at the ICOM PROIII manual.

The phone jack on the front of that radio is rated at 5 milliwatts output max. which makes sense so you do not hurt your ears.

The speaker connection on the on the back of the radio has a full 2 watts of audio output.

Hope this helps, Jeff K9JP


Thanks to suggestions here, my problem is solved.

I had the speaker connected to the audio jack on the rear of my Flex 6300 and the audio was too low.

I tried the audio jack on the front of the Flex and the audio was excellent!

I found that by adding an additional inch of pipe, the response was even better..
Again, thanks to all who tried to help.
Andy, k2oo


As shown in the photo in QST, the speaker has a resonant frequency of about 900 hz.

By adding an extension, you can vary the resonant frequency.

My results are as follows:

1 inch extension resonates at about 750 hz

1.5 inch extension resonates at about 650 hz

2.0 inch extension resonates at about 600 hz.

Personally, I find the 650 hz to be the most comfortable.

73 Andy, k2oo

REM :Hi Hi 1

I've really enjoyed my CALF CW audio filter.

You can choose the width all the way down to 80hz. And I've used 80hz but mostly use 500hz and 200hz.

73s & Enjoy! N4IVE - David Gale


Resonant (tuned) CW Speaker Build by John W2IU

Building a Resonant CW Speaker by Steve Ellington

They sound beautiful and much better than an electronic filter because they do not ring - Very mellow sounding.

Also they allow you to use fast AGC and QSK without all the usual unwanted noises.

Texas Tumbler - Acoustic Resonance CW Speaker by NG9D

This clip illustrates sound resonance in tubes with one open end and one closed end

where the even numbered harmonics are missing in such instruments as flute and clarinet.

How to find the frequency at which an object vibrates the most.
By hitting a solid object this will vibrate at its own resonant frequency. The emitted sound was recorded using a photo camera's video recording function and once more by the pc headset's

REM : Hi Hi 2

Water's oxygen hydrogen bonds can be broken in many ways resulting in high energy outputs that are stored in water.

Since water contains an enormous amount of energy, the potentials are endless.
This video demonstrates a single method of water bond breaking using radio frequency.



Novice Rig Roundup FINALLY made it into QST's Contest Corral after 3 years of trying!

Not only that but we somehow got TWO LINES (LOL.)

See Page 97 of February 2017 QST.

We are also on Page 154 and 3/4 of the way down the right hand column! NRR is GETTING ON THE MAP!!

ANNOUNCING NOVICE RIG ROUNDUP 2017!!! The dates are 0000 UTC on FEB 18 through 2359 UTC on FEB 26, 2017 - that is 9 full days (UTC.)


Bry Carling AF4K


Not all of me will die - - - The good I do will live forever.


Palm single lever paddle as cootie key.

Has anyone tried the Palm single lever paddle which can be switched to cootie mode?

Carl j mannle N6TVN.

The Palm paddle - and all paddles can be used as sideswipers.

People say the Palm paddles are way too light.

Take a look at:

as they have paddle fingerpieces - those are the ones that are flat, that you can use to convert a single or dual lever Vibroplex to a sideswiper.

73, David N1EA




Terminated Coaxial Cage Monopole by Martin Ehrenfried G8JNJ

I took the G5 and went along with a G5RV in the QRN... but at least this mistake which led me to discover an unknown antenna to me and even another one @

where I learned a lot more today !!
73s & 77s, 

See Attachment pse
Thanks fellows, have a nice weekend, BCNU.

73, Yann, F5LAW. SideSwiperNetGroup


73, from the town at the rivers "De Bergsche Maas" and "De Dongen" Geertruidenberg (800+ years city rights) at: 51.702211N 4.853854E

Your Editor Jan Pieter Oelp PA3CLQ



My simple website about Gigantic DF-Antennas

Part 1 "DF-Antenna Wullenweber Array"

Part 2 "DF-Antenna USSR Variants"

Part 3 "DF-Antenna USA Variant"

Next Part 4 "USSR OTHRA DUGA 1,2 & 3" at: