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Since almost 30 years, for my portable VHF activities, I used a F9FT 9el yagi. This one was the best available for this purpose, it was leigthweight, relatively cumbersome and performed quite well. Unfortunately, it broke during a contest when falling down from 7m high...
To replace my beloved antenna, I decided to build something and not to buy one. After searching some design on internet, I finally adopted DK7ZB's one. He offers several designs, and iIchosed a 7 element yagi in 28 Ohms technology.
The advantages of DK7Zbs antennas are :
- Computer optimized
- Great reproductibility
- Easily assembled and dismantled. Ideal for portable operations.
- Excellent electrical characteristics, gain, pattern, F/B ratio.
The original version described on DK7ZB's page has a 3.26 m boomlength. So, I asked him if he could calculate it for a 3m boom. Aluminium tubing are sold in 6m length, and with 3m booms i would be able to build 2 antennas. The new calculated antennas have a small gain drop (about 0.35 dB)
Another advantage of this 7el is that with a 6m long alu tubing, you have enough for all elements and build 2 antennas.
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This page is a short description of the four phased verticals system i've build and used. It is primarily intendend to be used on the lower bands 160m, 80m, 40m. All the principles stated here are of course valid for any other bands, but you can achieve the same game with yagi antennas easily. It is mainly built around the Collins hybrid phasing system wound on toroids.
Other feeding methods are possible and certainly better, but this one is rather simple to build and use on the battlefield. (contests, fieldays, expeditions)
Many stations use this system all around the world and it has proven his effectiveness.
Four phased verticals on 80m (click to enlarge)
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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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For one of my projects, I recently bought on Aliexpress (see links at end of article) a Chinese fan speed controller board.
I was struggling to understand how this board can be set, the instructions found on Aliexpress being nearly of no help. The Chinese to English translation is.... :-)
Here is what I found ... 
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During my SOTA activities, I often raged on the fact that the builtin CW keyer in my QRP SW-3B transceiver only had one memory ... It is indeed very practical to have several of them in order to free your hands to do something else such as finishing writing the last QSO on the logbook or making a somewhat specific call. The idea therefore sprouted to produce a CW memory manipulator that would meet the following conditions |
- 3 on the fly programmable memories
- low power consumption
- easy battery supplying
- reduced size
- easily reproducible
Having already built a prototype of the fabulous K3NG keyer, I decided to use this project by adapting it to my needs.
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Our corsican repeater network TKNET uses the AllStarLink (ASL) software for the routing and communication between nodes needs a USB Radio Adapter (URA). In order to digitalize the audio signals and interface them with the repeaters, i developped a small interface board some years ago. It was using a cheap USB audio stick that we modified and plugged on my board. With time, this solution appeared to be not the best choice for different reasons. So, the idea to build a newer board with an onboard USB audio chip was born. Being retired, I found the time and mood to develop a new interface board using the same chip CM119A which is a small LQFP-48 case. |
Features :
- Onboard USB sound card compatible USB 2.0 and 48 kHz sampling rate.
- Powered via USB port or onboard stepdown regulator, jumper selectable
- Watchdog locking the PTT output in case of communication problem with the controler.
- 4 monitoring LEDs, Heardbeat, Squelch, PTT & OK.
- Left/right transmit audio channel jumper selectable
- Squelch level jumper selectable, ground or high level (open squelch)
- PTT output can be cut via jumper or switch (for tests, relaying OFF, etc...)
- 5 GPIO available, software programmable.
Connectivity :
- 2mm power Jack to power the onboard 5V/3A power supply (max 30V input)
- Port USB B for IN/OUT and connexion to computer or Raspberry board
- Port USB A to power an external board like a raspberry via a USB cable (USB C, etc...).
- DSUB- 9 female connector for RADIO inputs/outputs (PTT, SQ, AF TX & AF RX)
- GPIO4 to GPIO8 available on onboard pin connector.
Operation :
The board has its own power supply build around a small DC-DC buck converter that can power the interface and an external board (such as a RaspberryPi) via the USB A type connector. The input is max 30V and it can furnish 3A. The output is protected by a fuse F1.
A jumper can select the power source for the board the internal PS or via the USB A connector.
The heart of the interface is a CM119A chip that has a USB transceiver, voice DA + AD converters and 8 GPIO ports.
It has an oscillator with an external 12 MHz crystal.
The LED0 output on pin 12 drives the Led HB (heartbeat) that monitors the CM119A state. Blinking shows a USB dialog and steady that the chip is powered and waiting.
This LED0 output is also used to drive a Watchdog build around a NE555 triggerable astable. As soon as the LED0 stops blinking, the Watchdog puts the NE555 output in a LOW state. Transistor Q4 is not driven anymore and locks the PTT line via Q3 which is the PTT switch.
The Watchdog is preventing a steady carrier situation if the controler software crashes.
The PTT function is done via CM119A pin 13 GPIO3. Transistor Q3 drives the transmitter. The jumper JP4 can be used to interrupt the PTT line in removing this jumper and/or wiring a front panel switch.
The Squelch input drives transistor Q1 to pin 48 VOLDN and tells the software that a carrier is present.
Jumper JP2 allows 2 Squelch states :
WITHOUT : the receiver must provide a voltage when NO signal. Max. voltage is 5V, even if there is a 5V Zener protection on board.
WITH : the receiver must provide a close contact when NO signal. A 5V is then present on the input.
The right or left audio channel at CM119A outputs are selectable with jumper JP3 and driven to the transmitter via the RP1 variable resistor.
Resistor R7 in serial with RP1 can help to adjust the output level setting. Some transmitters do need a very low input level and the RP1 setting can be a little critical. R7 can be omitted in most cases and replaced by a wire jumper.
The AF signal from the receiver is driven to pin 27 MICIN via the RP2 variable resistor.
Building the board:
The printed board has been drawn with EASYEDA. PCBs have been ordered at their partner JLCPCB which i use regularly to my great satisfaction ! Recommended !
The big advantages of EASYEDA is that it doesn't need any installed software, is Web oriented so allows working from anywhere on this planet and with a team. (even if i did it alone..)
BOM bill of materials ODT format with MOUSER references. Some components were ordered via Aliexpress.
Component side of the board
Solder side of the board
The most difficult task is to solder the CM119A which is a LQFP-48 case. But with a small soldering iron, a good view (i wear glasses), solder flux and a calm hand (i have one), the job can be done ! I did it at my age and bad close view ;-)
I double checked the continuity from the CM119A pins with the help of the schematic. Check solder bridge as well.
As often, the first version of a PCB has some errors, i didn't make an exception. I made 3 small silkscreen errors.
BEWARE, the diagram and picture in this article are the good one, the concerned parts are marked with a red dot on the component side view above.
Only the PCB made on version 03/2021 have these errors.
- R4,R9,R12,R17 470 Ohm for brighter LEDs an correct an error in R17
- Diode D2 1N4148 reverted
- Diode D1 BAT43 reverted
- Resistors R10 4.7k & R11 1M have been swapped (around NE555)
- R13 & R16 values are 2.2k not 10k
If the board is to be powered via the USB B connector and if the internal power supply is not used to power the board and an external controler board, like the Raspberry Pi, the following parts can be omitted :
- DC1 power connector
- DC-DC buck converter U1
- Fuse holder F1
- Jumper JP1 replaced by a wire jumper in USB position.
- USB1 connector
The rest of the wiring is correct and does not need comments. Only the value of resistor R7 in serial with RP1 (TX level) has to be changed in order to adjust the output level to your transmitter needs.
R7 forms a voltage divider with RP1 and allows to adjust the setting coarse. It can be replaced be a wire jumper in most cases.
C3 on the USB port supply is not mandatory and can be omitted if no problem. (i didn't have any)
BEFORE powering the board, inserting the fuse and jumper JP1, you must ABSOLUTELY set the output voltage of the DC-DC stepdown regulator LM2596 in order to have a precise 5V on the output ! Very often, the boards come with the variable resistor at full value and the board delivers >12V !!
Tests :
Make a loopback between the audio ouput and input in bridging pins 1 & 2 on the DSUB RADIO connector
Put jumper JP1 on the USB position in order to power the board via the USB port.
Connect the board to a computer with a USB A-B cable. The HB Led should light up showing that the board is powered and Windows should detect a new audio device "USB PnP audio device", as well as a new composite device.
At this stage, the HB Led should be steady and the OK Led OFF.
In the sound parameters, the new device should appear in both INPUT and OUTPUT device selection.
Select it in both.
The HB Led should blink and the OK Led should light, showing that the Watchdog is working fine.
Load and read a sound file and check if the level gauges are moving for both Input and Output.
Check that both levels are adjustable with the RP1 et RP2 adjustable resistors.
Unselect the new sound device, the OK Led shoud be OFF and the HB Led steady.
If everything is OK at this stage, congratualtions ! If not, start to check the board wiring... :-(
The JP2 jumper is modifying the Squelch operation :
Without jumper : the squelch signal from the receiver should provide a voltage when Squelch is unactive (5V max) and 0V when active.
With jumper : The squelch signal from the receiver must be an open collector and short with inactive Squelch
Test : Insert a jumper on JP2 , the SQ Led should light. Put the SQ input on DSUB RADIO pin 4 at ground, the LED should be OFF
The PTT line can be tested with a small utility found in the DireWolf package, namely CM108.EXE (release download page) which switches the GPIO3.
In a DOS CMD window, launched without parameters it lists all sound devices :
Copy the complete line with the HID number and launch the following line for the above example :
cm108 "\\?\hid#vid_0d8c&pid_013a&mi_03#7&27055985&0&0000#{4d1e55b2-f16f-11cf-88cb-001111000030}"
The PTT Led should blink at a 1s rate and the screen show a list of 10101010101. The PTT line (pin 5 on DB9) should also be activated on the same rate.
Commissionning :
Put a jumper on JP1. USB side if the board has to be powered via the USB port or INT side if the internal power supply i used.
Put a jumper on JP2 if the Squelch signal is a open collector output. (see details above)
Put a jumper on JP3 on L or R depending of the audio channel used in the controler.
Put a jumper on JP4 in no switch for relaying in not present on the front face. (see details above)
Connect the USB B cable to the PC or controler board.
Connect an external power supply on DC1, max 30V/3A. (if needed)
Launch the controler software. The HB Led should blink and the OK Led light ON. Check the good working and adjust the audio levels with help of the software and the RP1 & RP2 pots.
DSUB RADIO connector wiring :
- 1 - RX AF coming from receiver
- 2 - TX AF going to transmitter
- 4 - SQUELCH signal coming from receiver, 5V max or open collector.
- 5 - PTT signal to transmitter (open collector) 15 V max.
- 3+6+6+7+8 Ground
- 9 N.C
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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...
PSU
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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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 :
- Step-start
- 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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Here 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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Vous trouverez sur cette page quelques informations sur les câbles coaxiaux qui pourront vous être utiles.