3CPO Code Practice Oscillator / Keyer / Trainer

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3cpov2-left2 3CPO-H-Front 3CPO-KIT


3CPO combines a keyer, Twin-T oscillator, and transmitter keying circuits into a single unit.

  • Modified DK3LJ YACK memory keyer IC
  • IAMBIC key training mode – learn how to send with a keyer!
  • NEW – Advanced IAMBIC training mode – code will speed up or slow down as you make correct or incorrect entries.  When you are done a score of your results is played back.
  • NEW – Straight key detection.  Just plug a straight key with mono jack in and 3CPO will automatically go into straight key mode on power up.
  • Beacon mode
  • QRS button
  • Twin-T oscillator with wave shape circuitry provides a near sine wave signal properly shaped for CW
  • Audio tone range: 300-1,000Hz
  • Ability to key many rigs using both positive and negative grid key interfaces.  Tested on:
    • Heathkit HW-7, HW-8, HW-16
    • Icom IC-271, IC-725
    • Kenwood TS-520 TS-530
    • Yaesu FT-290RII
    • 4SQRP SS-40 and Cyclone
  • Protection circuitry on the keyer input and power supply polarity.
  • Hardware reset to factory defaults.
  • Kit includes instruction manual, all parts, connectors, speaker, and chassis hardware. Just supply your own case!

Click here for 3CPO-Manual, Schematics, and Operation manuals.

See the Code Practice page for more details.

********** OUT OF STOCK **********

(more coming in March 2018)


3CPO-KIT 3CPO-H-Front 3CPO-Kit1-M

3CPO Kit w/ Enclosure

Item: 3CPO-EK     Weight: 16oZ

Kit: $55

Assembled: $80


3CPO Kit only (no enclosure)

Item: 3CPO-K     Weight: 8oZ

Kit: $35

Assembled: $65

Add an Enclosure to 3CPO

3CPO-Encl-Fr 3CPO-Kit1-M


3CPO Enclosure

Item: 3CPO-E     Weight: 8oZ



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Chinese Super RM Rockmite AKA Octopus

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These kits usually come with a 7.023MHz crystal(s) which are in the EXTRA class bands.  Check out the Crystals page to move these little rigs to the General Tech/Novice frequencies.

Looking for a good English step-by-step guide to assembling your Super RM Rockmite?  Need Troubleshooting information?  Try this:

Super RM Assembly Manual


Follow THIS LINK for a neat enclosure you can build by VE3FWF.



Here is an English version of the software: RockMite51-English.zip (30Mb)

Note: I do not personally use the software and have bypassed the Keyer IC but the READMEFIRST.txt does have setup instructions.  After that your on your own…….Best of luck!

Kit Cost: $30

Kit Contents:

Bag of Parts, Printer Circuit Board, Schematic (blurry!), Parts list, Layout page.

No other instructions, however, instructions available on-line.

A zip file of instructions & schematics is available here.

BEWARE OF BAD TOROID CORES and BAD/Low Voltage Capacitors!

Several incidences of Rockmites with low power output (1-3W) were the result of bad T37-2 (red) toroid cores.  In each case good T37-2’s were replaced resulting in 5W output.  Be suspect of cores with a red texture to them.  The good toroids should be smooth in appearance.

There is also reports of some disc capacitors being bad.  Good or bad consider upgrading to 100V or better capacitors in the final amplifer, low pass filter area, and input to the receiver section.  More than 50V can appear in these areas at times which is marginal since these appear to be 50V caps.  Check and replace C4 (33pF),  C8(100pF), C9(470pF), C11(470pF), C12(1000pF), and C25(AKA C26 .1uF).



 ***** 2017-04-04 UPDATE *****


It’s been a while since playing with the Rockmite.  Thanks to Bernie, VE3FWF, I now have this cool LASER cut enclosure to put it in.  As long as we’re adding an enclosure I tricked it out with Pixie Switches, Super VXO, and replaced the keyer chip with a YACK engine.

VE3FWF Enclosure Plans (.SVG, .PDF & .JSON files) along with SVXO instructions are available here:


Rx Filter Pixie switch

& YACK Keyer Engine

Pixie Switch

& Super VXO

Top view almost together Ready to play!

There are a few caveats with it all together.  The VXO drops out at the extreme end of the band but not enough to worry about.  Along with the VXO the Tx/Rx offset varies from -1KHz at the low end to almost zero at the high end.  This was predicted when playing with Super VXO’s earlier this year.   Retro-fitting the YACK engine was the hardest part as the button logic was entirely different.  The YACK sidetone is also a little on the loud side so maybe a little resistor divider or trimmer might be the next mod to adjust the sidetone volume.

The SuperVXO gives a nice range with the following:

Switch Low High
A 7036.6 7046.2
B 7045.2 7056.2
C 7100.0 7115.2
D 7110.6 7123.2
Tx Offset -1KHz 0Hz

Super VXO Parts:   150pF PolyVaricon, 15pF cShunt, 18uH Toroid w/ 4.7uH Axial.

STM to YACK conversion:

STM YACK Function
1 1 Reset
6 7 SW4 (Now QRS/CMD/PLAY1)
10 4 Ground
12 5 Tx
14 6 Sidetone
15 2 DAH key
16 3 DIT Key
20 8 +5V

The following mods are also needed for YACK:

Add a 4.7K resistor between pins 20 and 6

Pull R27 (reset resistor) – move between pins 1 & 6

Remove R17, R18, & R21 next to the switches

Add a 1K between R18 and R21 (or a 510+560 Ohm) on the switch side

Add a 1.8K between R21 and R17 on the switch side.

Switch SW4 is now the QRS button

Switch SW3 is now the Command button

Switch SW5 is now the Playback-1 button

And now back to our regular scheduled program……….


  • The same issues as the Pixie above sans the color coded inductors as there are none.
  • Schematic diagram was blurry and hard to read, impossible in spots.
  • Kit was missing a 2.2K resistor but ended up with an extra 22K resistor as well as extra .1uF (104) and .01uF (103) disc capacitors.  Kit was also missing the 10uF capacitors but received extra 1uF capacitors.
  • There is a location next to the audio jack for a 100pF capacitor.  This is not marked on the schematic but installing it had no effect.
  • There were NO instructions on what the inductor values are or even how to wind them!  Fortunately KB2HSH’s web site had instructions.  Can also be found on the SUPER-RM Yahoo group.  There are several versions so make sure you download the correct one!
  • The hole for the BNC center connector is slightly out of  alignment and too small.  I ended up breaking the flimsy wire and fixed by placing a small piece of wire in the PCB then splicing into the broken end.
  • In a few areas non-joining pads are spaced too close together.  Watch your soldering and excess lead lengths for shorts.
  • Winding the toroids are not too hard to do.
  • Pick up a strip of break away machine pin headers.  Break into 3 pin sections and remove the middle pin.  Then insert these into the 3 frequency selective crystal areas.  You can then easily change frequencies by swapping crystals.  Note: you may end up with a little more noise by not grounding the 2 input filter crystals.
  • RIT is a trimmer and should outright be a potentiometer w/ knob.  A good upgrade is putting this in an enclosure.
  • NO Mounting holes!  Assumes you are using an enclosure designed to exactly fit the PCB.

Operation and comments:

I’m getting a nice 5W signal from the Tx output.  This is with a cheap 1A 12.0V power supply.  The Rx also works but there are some issues overall:

  • The Program in the micro is not great. it could use a major upgrade!
    • The DIT and DAH inputs do not auto repeat.  Makes the keyer useless!
    • The Sidetone only has a few different tones and sounds funny.
    • Have not even attempted to try the serial port/software.
    • Could not get it into straight key mode!
  • Since I have my own keyer,  and don’t like the tone even in straight key mode, the following modifications were performed:
    • Remove the CPU and MAX232 IC’s – they are not needed.
    • On the CPU Socket Jumper pins 12 (Tx line) and 15 (keyer tip jack) with a piece of wire.
    • Jumper a 4.7K pullup resistor between pins 15 (Tx Line) and 20 (+5V).
    • Snip the lead of resistor R10.  This 470 Pullup is too much for the 3CPO keyer (or jumper D501 on 3CPO instead of the 4.7K pullup and R10 snip).
  • There is a horrid tone on the audio around 7.5-11KHz.
    • The problem is somewhere in the audio circuitry.
    • The problem is there with the SA612 mixer, micro, MAX232, and Osc xtal removed from the circuit.
    • By lifting pin 1 off the op amp and using a simple 470K resistor makes the tone less harsh (still present).  Of course you can’t drive your headphones this way.
    • Looking at the circuit between the 2 op amps I knew something just didn’t feel right.  My guess was no resistor between the 2 sections, effectively giving the second stage a very high gain (Rf/0=infinity) and causing oscillation.  Here is a simple solution:
      • On the bottom of the board, cut the trace between U3 pin 7 and where is leads to capacitors C14&20.
      • Place a 50-200 ohm resistor between U3-7 and C14.
      • I used a small trimmer and found anything below about 25 ohms causes oscillation.  Going above 25 seems to have little effect except to slightly alter the overall noise tone.
  • With the keyer and tone problems solved this is looking like a neat little rock bound QRP rig!
  • FLDigi and HRD receiving software does not work well with this board as it sits.  I believe this has to do with the way the 2N7000 driver is configured.  However, tapping directly off pin 1 of U3 using a DC blocking capacitor (10uF) with no attenuator between radio and computer seemed to work the best.
Super-RM-bypass-Mod Super-RM-Audio-Mod

Additional information & pictures for the 131019 build (Click on each to enlarge)





Y1 and Y3 uses a socket for a Pixie Switch.  Y2 is bypassed with a jumper and C3 is removed.






U4 Bypass

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CW Kits

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(Click on the pictures and titles for detailed information and assembly manuals)

We can also build the kit for you! Assembled prices are in th



Configurable Audio Limiter Filter

Is QRM and QRN getting you down? Don’t have a cow, get a CALF!   CALF – the Configurable Audio Limiter Filter is designed to help pull signals out of the QRM and noise with bandwidths down to <100Hz and skirts up to 40db/octave on a 700Hz center frequency.  Includes experimenter options.



The little brother of the 3CPO Iambic keyer/Trainer



Code Practice Oscillator & Keyer

3CPO combines the DL3LJ YACK keyer IC w/ Iambic trainer, a Twin-T oscillator, input protection, and a positive/negative transmitter keying circuit into one unit. The Twin-T oscillator provides a near-sine wave along with properly shaped audio CW signals.

e detailed pages. Contact us if you would like a kit built but assembly price is not listed.

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Mini-Yack Iambic Keyer/Trainer

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Mini-Yack (Yet Another CW Keyer) is the bare bones little brother of the 3CPO keyer and iambic trainer designed for embedding into a QRP radio.  Included within the YACK engine are 2 memories, a beacon mode and 2 Iambic training modes.


NEW Advanced Iambic Training Mode – Is it a training or is it a challenging game?  The new advanced Iambic training mode will send a call sign which must be properly re-entered with Iambic paddles.   On each successful entry the keyer will advanced in speed by 1WPM and on each wrong entry will decrease by 1WPM.  When training is complete (by pressing the COMMAND button) the keyer will return to the default speed and send what the last speed during the session, the number of calls entered correctly and the total number of calls sent.


Mini-Yack-BoardMini-Yack Mini-Yack-ButtonsMini-Yack Buttons
 Mini-Yack-Connected Mini-Yack-HW-8SMini-Yack Inside an HW-8
Follow THIS LINK for a neat enclosure you can build by VE3FWF.

Comparison of the Mini-Yack to 3CPO

Mini-Yack 3CPO
Side Tone Square Wave Twin-T Shaped Sine
Side Tone Adjustable? Yes Yes
Iambic Trainer Yes Yes
Straight Key Bypass Yes Yes
Memory 2 @ 100 Characters each 2 @ 100 Characters each
Beacon Mode Yes Yes
Keying Positive Only Positive AND Negative Grid
Input Voltage Protection Yes Yes
Key input protection No Yes
Power 2*-15V 8-15V
Buttons Command Only on board

PLAY1, PLAY2, QRS, RESET, and Command External Buttons Available

Command, QRS, Play1, Play2, Reset, Power
Factory Hardware Reset Yes Yes
Enclosure Available No Yes
Price $12 $35

Download the Mini-Yack-Manual

Want to add more or different features?  Hack the Yack!  The YACK code is open source to view and modify. Mini-Yack-Source.


Mini-Yack Keyer

Item: Mini-YACK     Weight: 3oZ

Kit $12

Assembled $16

Mini-Yack Options



ATTINY85 Chips

Item: ATTINY85     Weight: .1oZ

Select from Blank, Mini-Yack, or 3CPO, or Yack-original





VE3FWF, LASER cut enclosure:

Enclosure Download: VE3FWF-Enclosures

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QRP Radios

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Heathkit HW-8 CALF-3CPO-HW-8
Chinese QRP Kits Pixie2
DC Receiver Tuning HW-8-Dial
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Station Accessories

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Audio Attenuator Audio-Attenuator-V2-Board-small
Reverse Polarity Protection RPP-in-HW8
Code Practice CALF-3CPO-HW-8
CW Reception CALF-H-Front
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Cables and Adapters

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Stereo Cables

These cables are about 36″ (1m) long with 3.5mm stereo ends.

Use to connect CALF, 3CPO, HF digital interaces, etc. to your radio.

Stereo Cables


Weight: .5oZ



Several colors are available.  By default we will close our eyes and pick a random cable color from the box unless you let us know otherwise.  Quantities available in parenthesis.




Red (12) Green (20) Blue (10)
Orange (8) Violet (4) White (10)
Peach/Pink (6)  Black (10)






Weight: .35oZ


6.35mm (1/4″) Male Stereo ->

3.5mm (1/8″) Female Stereo

Great for older rigs with the larger speaker and key jacks.


Weight: .35oZ


3.5mm (1/8″) Male Stereo ->

6.35mm (1/4″) Female Stereo

Great for older rigs with the larger speaker and key jacks.



Weight: .13oZ


3.5mm (1/8″) Male Stereo ->

3.5mm (1/8″) Female Mono



Weight: .13oZ


3.5mm (1/8″) Male Mono ->

3.5mm (1/8″) Female Stereo

 Adapter-3MM-D3FS ADAP-3MM-D3FS

Weight: .13oZ


3.5mm (1/8″) Male Mono ->Dual 3.5mm (1/8″) Female Stereo



Weight: .13oZ


6.35mm (1/4″) Male Mono ->

Dual 6.35mm (1/4″) Female Mono





Weight: .13oZ


6.35mm (1/4″) Male Mono ->

Dual 3.5mm (1/8″) Female Stereo


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CW Reception

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 CALF-3CPO-HW-8 HW-8, 3CPO, and CALF


New – CALF Vs NESCAF Smackdown Comparison.  We compare the NESCAF switched capacitor filter to the CALF active op amp filter.

Read the article:  NESCAFvsCALF.pdf

Audio samples: NESCAFvsCALF-Audio.zip


I have a hard time concentrating on CW when multiple signals are heard at the same time.  Maybe it’s due to my hearing impairment (Yes, even one eared I do play music and copy CW!).  For me I try to copy everything I hear, high and low, which results in gibberish and missed characters.  Just after creating my HW-8-LM386 audio amplifier, I met up on the HW-8 Yahoo reflector with Glen, KK4LPG, which re-introduced me to op-amp audio filters.  Glen happens to be a wealth of knowledge in op-amp filtering and pulling in weak signals.

The CALF (CW Audio Limiter Filter) project began as a simple way to improve the not-so-great filtering of the Heathkit HW-8.  My first thoughts were to remove the LM3900 IC and replace it using a piggy-back PCB with better filters on it.  The project began growing after looking at some of Glen’s ideas of adding a limiter (and LED display) to the circuit.  So why should a limiter be in the circuit?  There are many good reasons!

  • Several great articles by N7VE discuss filtering and the need to add a limiter circuit to protect your hearing.  This makes sense in saving your ears when you turn your volume way up to hear a weak signal only to go deaf from a large static crash.  Although in this circuit the limiter is at the front of the circuit instead of just before headphones, it still helps.
  • In relation to static crashes above – Take for example trying to listen to an S5 signal with a summer lightening storm a hundred miles away generating S9+10 static crashes.  The storm takes the foreground while your signal takes a back seat.  Now add a limiter in the circuit setting the limit threshold to just above your S5 signal.  Anything over that, such as lightening crashes, is limited (think of it as cutting the positive part of a sine wave in half and squaring off the top).  You still hear the crashes but they are now more like S5 or S6 crashes against your S5 signal… a level playing field!
  • In a weak signal environment you can use a limiter to it’s limits so to speak.  For example take a nice quiet day on 15M (no lightening, just background noise) and you hear a faint signal.  Placing the limiter up until the background noise itself is limited may sometimes make that signal sound stronger.  Maybe it’s a trick of the ears but it really does work!
CALF on the breadboard – not pretty but works!

So now at this point there is a limiter as well as bandpass filters on the protoboard.  The gears started rolling with questions…….

  • How do I add the limit control and LED’s to my HW-8 without drilling into the case?  (no good answers here!)
  • Will it work with my other rigs?  The HW-7?  The HW-16?  The IC-725?  The TS-520?  (yes it does!)
  • Can I even fit this larger circuit in my HW-8 where the LM3900 goes? (if I used SMD devices it could)

With those questions a decision was made to make it external to the radio, polish it up a bit with some input buffering and an output amplifier, and create a PCB for it to keep the project clean looking.  Because I like to tinker with circuits I thought ahead and added a few other goodies to the PCB such as the ability to socket the R/C values to make different types of filters (High, Low, and Band pass!) and to add jumpers to be able to re-arrange the limiter and filters as needed.  The power switch is also an audio bypass allowing the audio signal from the radio to go straight to the speaker/headphones when the power is turned off.


 CALF – The CW Audio Limiter Filter
Experimental Version with R/C values in sockets


How does it perform?  Well first I have a disclaimer…..  Compared with one of my IC-725’s with a built in 250Hz IF filter, there is no comparison.  An IF filter will easily outperform strong signal interference compared to any AF filter, even a DSP one.  That being said, there are still plenty of reasons to use an AF filter.  For many commercial radios cost is a big issue with IF filter prices going from $100-$250+!   Other radio’s may contain an IF but a filter is not available (buy custom Xtals and roll your own!).   Yet for many QRP type radio’s, such as the HW-8, there is no IF to filter.   In these cases an AF filter is better than no filter at all!  Personally I prefer the sound quality of CALF over my IC-725 narrow IF fiter.

That being said, it does a pretty good job.   Along with the bandpass filtering, the limiter really does help the signal.  Both during static crashes as well as trying to grab that signal in the noise floor.    The filter was designed with a 700Hz center frequency.  Although there are 6 stages of filtering, only 5 are actively selected with the switch.  3dB Bandwidths were measured as follows:

 700Hz   Measured as 689Hz with a 5db/octave roll off - Great for AM/SWL listening
350Hz    Measured as 360Hz with a 13db/octave roll off  - Great for SSB listening
175Hz    Measured as 159Hz with a 34db/octave roll off
125Hz    Measured as 117Hz with a 41db/octave roll off
<100Hz   Measured as  79Hz with a 41db/octave roll off - A little too narrow to tune with the HW-8 unless tuning with a lower position first.  However once tuned worked great!
calf-proto1-100mv-manualMeasured response of CALF


Here are a few audio samples.  In each sample is a few seconds without filtering then the same sample played again with the limiter/filter:

40M on a bad day

40M with Buzzing sound



Noise, QRM, and QSB


Example of working with High and Low pass circuits.  Section 1 is High pass, Section 2 is Low Pass.  The resulting plot shows each filter along with combining them in series.  Note in the picture we used a jumper to bypass stage 1 for a stage 2 only measurement.  In this test the center frequency was 1200Hz.






 Want to design filters for the CALF?  Check out the TI FilterPro cheat sheet page.

Sometimes I get a request for a specific bandwidth or center frequency, so at the bottom of this page I will post values for requested settings.



CALF-V2-MANUAL – including parts list and schematics

CALF-Coral-PDF – Build a PCB enclosure for the CALF – details below

Interested in experimenting or need a nice filter?  Kits are available and can be found in the store.



CALF now has an enclosure but here are a few pictures getting from point A to point B…….

CALF-v22-frontA naked new born CALF CALF-Coral-Proto1sThe first rough coral – Yes- that’s made from a piece of $.75 peel-n-stick floor tile! CALF-H-FrontThe final CALF coral



CALF & 3CPO on Batteries

CALF  & 3CPO will run on batteries (for example 9V or a bank of AA/AAA’s).  It’s recommended to be closer to 12V or to use at least 6-AA’s.  Connect the battery positive (red) to the positive power terminal on the CALF/3CPO.  Connect the battery negative (black) to the middle unused power jack terminal.  This connection is normally shorted to ground when nothing is plugged in and will open (disconnecting the battery) when external power is plugged in.

For the battery I usually find the 9V & AA/AAA battery holder wires to be real thin & fragile.  If you use the terminal blocks then you may need to solder a small piece of wire (or a clipping from a part lead) to the battery leads so the terminal block has enough to clamp down on it.  You may also want to use the mounting hole next to the power block along with a small cable tie to secure the battery wires down and keep them from breaking.


Values for specific CALF filters

Refer to the schematic for node numbers – Values in red indiciates parts NOT in the original CALF filters.

Currently these have not been tested only calculated.  We will update this page as values are verified.

Filter Type Fc BW Q N1 N2 N3 N4 N5 CALF-600Hz

600Hz bode plot

using (sub) values

1 BP 600 600 1 15K .01uF .01uF 56K 47K
2 BP 600 300 2 47K .01uF .01uF 100K 6.8K
3 BP 600 200 3 82K .01uF .01uF 150K (sub 200K)
4 BP 600 120 5 56K .022uF .022uF 120K 1.2K
5 BP 600 100 6 56K .022uF .022uF 150K (sub 470K || 200K)
6 BP 600 75 8 82K .022uF .022uF 180K (sub 200K)
Same as above except optimized using values existing in the CALF filters (red)
1 BP 550 550 1 27K .01uF .01uF 56K 27K
2 BP 550 275 2 62K .01uF .01uF 120K 8.2K
3 BP 550 185 3 91K .01uF .01uF 180K 5.6K
4 BP 550 110 5 68K .022uF .022uF 130K 1.3K
5 BP 550 90 6 82K .022uF .022uF 160K 1.1K
6 BP 550 70 7.8 100K .022uF .022uF 200K 820

500Hz Center Values – optimized using values existing in the CALF filters (red)

Filter Type Fc Bw Q N1 N2 N3 N4 N5
1 BP 500 500 1 33K .01uF .01uF 68K 33K
2 BP 500 250 2 56K .01uF .01uF 120K 8.2K
3 BP 500 167 3 82K .01uF .01uF 180K 5.6K
4 BP 500 100 5 82K .022uF .022uF 150K 1.5K
5 BP 500 83 6 82K .022uF .022uF 180K 1.2K
6 BP 500 63 8 120K .022uF .022uF 220K 820

500Hz Center Values – Using 0.1 uF capacitors

Filter Type Fc Bw Q N1 N2 N3 N4 N5
 1 BP 500  500 1  3.3K  .1uF  .1uF  6.8K  3.3K
 2  BP 500  250 2  5.6K .1uF .1uF 12K 820
 3  BP 500  167 3  8.2K .1uF .1uF 18K 560
 4  BP 500  100 5  18K .1uF .1uF 33K 330
 5  BP 500  83 6  18K .1uF .1uF 39K 270
 6  BP 500 63 8  22K .1uF .1uF  47K  180

450Hz Center Values – optimized using values existing in the CALF filters (red)

Filter Type Fc Bw Q N1 N2 N3 N4 N5
1 BP 450 450 1 33K .01uF .01uF 68K 33K
2 BP 450 225 2 82K .01uF .01uF 150K 10K
3 BP 450 150 3 120K .01uF .01uF 220K 6.8K
4 BP 450 90 5 82K .022uF .022uF 150K 1.5K
5 BP 450 75 6 82K .022uF .022uF 180K 1.2K
6 BP 450 56 8 150K .022uF .022uF 270K 1K


Calculated 450Hz Center Values – Using .1uF 5% capacitors and 5% resistors (KC9ON tested Preference)

1% resistors are preferred.  Note the last 3 stages are all Q=5 causing steeper skirts.

Filter Type Fc BW Q N1 N2 N3 N4 N5    CALF-450Hz-Preferred
1 BP 450 450 1 3.3K .1uF .1uF 6.8K 3.3K
2 BP 450 225 2 8.2K .1uF .1uF 16K 820
3 BP 450 150 3 10K .1uF .1uF 22K 560
4 BP 450 90 5 18K .1uF .1uF 33K 330
5 BP 450 90 5 18K .1uF .1uF 33K 330
6 BP 450 90 5 18K .1uF .1uF 33K 330


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USBTinyISP Programming Adapter

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Use this adapter with a USBTinyISP type programmer to quickly program ATTiny85 and ATMEGA328 (Arduino) IC’s. Works great with the Sparkfun Pocket AVR Programmer, Etherkit Etherprog, and others along with AVR Studio or Arduino software!  Can also be used as a mini stand-alone Arduino bare bones board.  Assembly manual can be found here.


Tiny-Adapter-328-Arduino Tiny-Adapter-328 Tiny-Adapter-85

ISBTinyISP Adapter

Item: USBTINY-ADAP     Weight 2oZ

Kit: $10 Assembled: $16


Note: ATTiny85 IC,  ATMEGA328 IC, and USBTinyISP programmer is not included in USBTinyISP Programming Adapters.

Add an ATMETA328P-PU or ATTINY85-20PU


Weight: .1oZ


(Free Bootloader Progamming)



Arduino Bootloader



ATTiny85-20PU ATTINY85-20PU

Weight .1oZ


(Free Programing options)








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Code Practice

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A few short years ago I decided to start playing with QRP and purchased an HW-8. Since this is a CW only radio I brushed up on my code using software called RufzXP until I was confident to have that first CW QSO in over 20 years. Although reading code at 15WPM went well I sure had QLF (Sending with the left foot) missing or hitting extra dah’s and dit’s with an IAMBIC keyer. It was even worse on a straight key! So in searching for a training tool I ran across the DK3LJ YACK keyer project and discovered it’s ability to be used to help train my IAMBIC fist. The only down side was the typical piezo buzzer / square wave oscillator…. that buzz buzz sound I can’t stand.

Last fall (2013) someone on the QRP-L mailing list mentioned wanting a nice sounding code practice oscillator.   That is when I decided to combine a twin-T oscillator into the YACK keyer. The result is a nice little keyer IC with well shaped CW audio.  A few extra goodies were added like reverse power protection, protection of the keyer inputs (every accidentally plug your -65V grid key rig into the key jack and watch the magic smoke?), and of course the ability to use either positive keying (for modern day equipment) or negative grid keying (for my TS-520 & 530). To add icing on the cake the controls are mounted to a second PC board to make chassis mounting easier and cleaner.

3CPO kits are available in the store!

Manual and schematics (v2): 3CPO-Manual.

CALF Coral – Drawings to make a PCB enclosure w/ Front & Rear panel overlays: CALF-Coral-PDF

CALF Coral Enclosures with overlays are available in the store!

Modified YACK Source Code: 3CPOv2-Source

3CPO View-smallFront-PanelSide-View-smallSine dit-dah

CALF & 3CPO on Batteries

CALF  & 3CPO will run on batteries (for example 9V or a bank of AA/AAA’s).  It’s recommended to be closer to 12V or to use at least 6-AA’s.  Connect the battery positive (red) to the positive power terminal on the CALF/3CPO.  Connect the battery negative (black) to the middle unused power jack terminal.  This connection is normally shorted to ground when nothing is plugged in and will open (disconnecting the battery) when external power is plugged in.

For the battery I usually find the 9V & AA/AAA battery holder wires to be real thin & fragile.  If you use the terminal blocks then you may need to solder a small piece of wire (or a clipping from a part lead) to the battery leads so the terminal block has enough to clamp down on it.  You may also want to use the mounting hole next to the power block along with a small cable tie to secure the battery wires down and keep them from breaking.

3CPO Alternate XMIT output test

The resistance checks in the KEYING circuit tests may vary depending on the DMM or VTVM being used.  Sometimes the DMM will only work for this test in the continuity setting which provide slightly more current, other DMM’s may need to be taken out of AUTO ranging mode.  In any case where the meter method does not work an alternate method of testing is available as follows:

Parts Needed:

  • an LED – any size of flavor
  • A resistor – The value is not critical but something in the range of 2.2 to 10K.  4.7K is a good medium value.
  • An isolated power source, such as a 9V battery.

Wire the circuit below.  Connecting P1 and P2 should make the LED light.

  • Connect P1 (Battery +) to the XMIT KEY+ and P2 (resistor free end) to XMIT GND.  The LED should light as you key down.
  • Negative grid block keying test – Swap the XMIT KEY+/GND connections.  The LED should still light during key down.


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