Harmonic calculator

Enter the lowest frequency in MHz for which you want to calculate the harmonics.

The calculator returns the theoretical wavelength (WL) and mechanical lengths for full (ML), half (ML/2), quarter (ML/4) waves.
The shorting factor used is k=0.95.

  F1 H2 H3 H4 H5 H6 H7 H8 H9 H10
WL (m)
ML (m)
ML/2 (m)
ML/4 (m)

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Universal K3NG rotor interface PCB

Description of a PCB, also called "shield" allowing to build a universal rotator interface based on the K3NG software. Only the AZIMUT function is supported.
This PCB has been thinked to be used either with a LCD display or an Ethernet shield to allow a remote usage via IP, and for a rotator using a variable resistor for the azimut value .  (HAM IV or CD44 in my case)

K3NG pcb nakedThe board includes :
- a 5V/1A regulator
- a header to plug an Arduino UNO and an Ethernet shield
- a HE10 male connector for to LCD display with a ribbon cable 
- a 5 pin DIN connector (+ ground shell) to connect the rotator control box
- 2 connectors for the "Clockwise" and "Counterclockwise" pushbuttons
- a multi-turn ajustable resistor VR2 for the azimut calibration
- an ajustable resistor VR1  for the LCD contrast
- 3 transistors for the CW, CCW, and BRAKE commands (open collector outputs)

I still have some naked pcb boards left. If interested, please feel to contact me.

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Avril 2017
I've been given a ICOM IC-R71E receiver that did not work and had been stored for a long time.
Symptom : no reception, no VFO or keypad action, no display.

RAM board

Symptom : no reception, no VFO or keypad action.

The Lithium battery on the RAM board which is plugged on the LOGIC board has been removed by the previous owner. The RAM board uses a static CMOS RAM uPD444C. When the backup battery is removed or flat, the datas stored in the RAM are lost.
The R71 has several parameters stored in this RAM, and when they are lost, the radio doesn't work anymore ! Some pretend that the processor is stored in this RAM. That's NOT THE CASE, it's stored in the processor ROM.
Only memory frequencies and mode shift are stored.

The cure is :
- send the radio back to Icom for repair (not sure if they still can do that after more than 30 years !)
- buy a third party RAM board, there are several on Internet. Look for IK2RND Roberto's offer.
- reprogram the board yourself !

Guess what ? I tried the last solution !
On Internet, i've found several infos about this problem and the easiest solution is the one offered by N2CBU. He has written a small software that can reprogram the RAM with the help of a simple programmer and file.

I quickly built this interface on a perf board. Durty but operational !

The main problem i had was to find a PC that was old enough to work under DOS at a relatively low speed and with a parallel port. 
I had to try 2 different PCs before it worked. In the BIOS settings, i had to change the LPT mode to EPP. Once i did this, it worked at first try !

After this repair, i could store, clear the memories and the display worked normaly. The keypad worked again, but i still had other problems. The 2 digits on screen displaying the channel number had some strange behaviour and the receiver was still mute...

DC-DC converter DP-2

Symptom : The receiver did not give any sign of life in CW/SSB/RTTY mode. I had some sound in FM only.
The S-meter was stucked at middle scale.

It appeared that there was no voltage on -10V line coming out from the MATRIX board.
The small metal case marked DP-2 was very hot and lately i had the L2 coil that made a lot of smoke and the PSU made some mechanical hum... In short, i had a short circuit !!

I unsoldered this DP-2 module and opened it. I made some reverse ingeneering and tested all components.
Meanwhile, i found another ham making the same work and who published the DP2 internal diagram. I measured the small transformer and the secondary is 2mH and the primary is a center taped 300 uH. Another ham had to rewind the secondary that burned and counted 125 turns and 2 times 26 turns for the primary.
Finaly "only" the 2SD648C transistor was burned.

I didn't have any substitution for this later, and i tried several transistors i had before finding one that worked and did not heat too much or did not burn after a while. I used a BD139 for which i had to file the legs until they fitted in the board. The transistor case is higher than the original one, and the module cover does not completely close the case... But that's not a big deal.

After that i noticed that C13 (100uF/10V) on the -10V output on the MATRIX board was short ! This was probably the reason of all this mess ! After replacing it and the L2 coil, the radio came back to life !
Finaly, i had a rather clean -9.5V on the -10V line. I had noise on all modes, and the S-meter was at S0 level !

But still the channel number display problem...


The PSU is known to be very badly designed. It heats a LOT and has a lot of problems. It is strange that ICOM engineers who have designed such a good receiver could design such a bad power supply !
Mine had 17.4V output , no regulation and getting very hot, heating all the cabinet !

At least for all my tests i decided to supply the receiver with an external 13.5V power supply with current limiter. The receiver consumes 1.3 A @ 13.5 V

I finally decided to have a look at the PSU. I checked all components, printed board failures and wiring, but found nothing wrong or broken. I double checked again and replaced the transistors, just to be sure. Nope !! Still no regulation ...
Just to be sure, i simulated the circuit with help of LTSPICE, and guess what ? The predicted output was 17V !!
Using LTSPICE, i changed the R2 resistor from 56 to 560 Ohm (what i had) and BINGO ! i got 14V at the regulated output.
I confirmed this by changing this resistor on the PSU board, and i got a clean variable 13.8V !

Is this a design error or do i have a particular situation with my board ??
For those interested, here is the LTSPICE file.

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Remote solution for TS590s

djcompact vignette
While setting up my remote station, I quickly have been confronted to the problem of the limitations of the remote ease of use. The first one is the ability to change the VFO frequencies. My logging software LOGGER32 offers a lot of macros and an option to use the mouse wheel to change the frequencies. But during daily traffic or contesting they quickly have shown their limitations.

 On Twitter, I have seen that several hams have been using a small DJ controller for driving SDR receivers and transceivers. So I started thinking to do the same for the TS590s.

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K3NG rotator via Ethernet

K3NG pstrotator

To be finished ...
While building up my remote station, i was looking for a solution to control one or 2 azimuth only rotators via the Internet.

There are several solutions and i finally adopted the K3NG rotator project i already used for a rotator controller connected via USB to my computer.
An Arduino compatible Ethernet shield must be plugged in the Arduino. The Ethernet shield is based on the chip W5100 and compatible with an Arduino UNO.

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HAM IV computer interface "à la K3NG"

To be finished...
Some years ago, i developed my own rotator interface with a PIC 18F452. In a need of another interface, i was unable to find my software sources of this project, lost somewhere in the computer Walhalla ! So, i looked for a finished project to build, and found the K3NG Arduino rotator project.

It looked very complete and having some recent experiences with the Arduino, i decided to give it a try.

What i needed :

  • Only azimuth drive
  • 2 lines LCD display (as i had several of them)
  • Eventualy 2 buttons CW + CCW to drive the rotator
  • Running on an Arduino Uno (as i had several)

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Arduino - save SRAM !

During the writing of my beehive monitoring project "Apaguard " using an Arduino UNO, i've been quickly very clode to the SRAM limit...

The Arduino UNO has "only" 2048 bytes of SRAM, which can quickly be filled if no precautions are taken.
Here are a few tricks i used during my writing, which permitted me to save a lot of SRAM and should be used by anyone coding on Arduino.

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Arduino - voltage measurements.

At first glance, measuring a voltage with an Arduino UNO seems to be a simple task. You only need to use the builtin A/D converter and the analogRead() function. But if you want to do this and get good results, you need to take some precautions and understand what you are doing !

Here my experience, and at the end i got very good results !

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TL922 facelift

A friend of mine who bought a cheap Kenwood TL922 power amplifier asked me to repair it and to bring some modifications in order to improve the security. This is the fruit of my works...

So, before any tests i have made the following modifications :
Filament transformer protection
HV protection agiainst internal valve flash
Zener diode substitution
PTT circuit modification ofr low voltage switching
RF relay substitution
RF stability improvement
Symetrical tube feeding

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TS590s intermittent receive

Since the beginning, my brand new TS590s had a intermittent problem. The reception was fading and sometimes disappeared completely. Sometimes, the TX went away and at the same time, the HI/SHIFT setting didn't work above 3000 Hz.
I noticed that a slight shock on the case brought the rig back to live, but not always. Being new and under warranty, i sent the rig back for repair.



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PIC tone decoder

decoderpicHere is a description of an audio frequency tone decoder build around a PIC 12F683.

For a cost not much higher than a basic NE567, you will have :

- A more efficient decoder
- Far better stabiliy
- A settable threshold with hystereis
- Possibility to tune from 100 to 2148 Hz or use a fixed frequency
- No exotic or particular component

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