Pulse Frequency Modulation IGBT controller

I have been asked by a friend to make a custom IGBT controller. Well, I heard about this marvels previously but didn't bother to read about more than the general definition.

I will not reiterate here all the theory behind the Isolated Gate Bipolar Transistors; who want to learn, there are several pages on the internet. 1, 2, 3.

After reading a lot of datasheets I decided that the best approach is to make a PFM generator working on 40-80 kHz with fixed 50/50 duty cycle, modulated with a PWM signal at around 100 kHz.
One big issue was that the 50/50  signal have to had a precise timing to match the Half-Bridge command mode. This is hard to achieve with microcontrollers but very easy if you use a specialised IC. So I start to look after this kind of circuits and found a lot of them!

The IC controller at choice was the IR2153 made by International Rectifiers (later aquired by Infineon).

Here is the waveform needed by a Half Bridge IGBT to work properly:

I did the schematic on a small breadboard and found it work from the first power-on! So, time to move on, to the variable PWM.
The simplest way to generate it was from a Arduino board using the lowest interrupt timer at 122 Hz. I wanted to use the interrupt timer because it's steady, precise and it's not affected by other "things" the microcontroller does. And I planned to do some nice things with it!

To keep the story short, I generate the signal with the Arduino, put the informations on a I2C LCD display (a nice bargraph, temperature and status) and did a test check-out at the Power On. More on that, on the small Youtube video I made. It's in Romanian but you get the point!

Here is the schematics and the code.
Oh, a big thanks to Damien Clarke who wrote a very nice library for reading analog values!!!

The CODE is available HERE ON THE GITHUB.

SE6861/12 mod AEG Telefunken manpack HF radio

AEG Telefunken SE6861/12 mod

Gama de frecventa : 1.5 - 30 MHz in pasi de 100Hz

RF output: 2W sau 20W PEP

Antena: baston 3.3 m

Antena tuner automat: ASG-6861 controlat de microprocesor, solutie de acord in max 5 sec, tipic 3 secunde, puterea de acord <10mw o:p="">

Modulatie: J3E (SSB) in LSB sau USB, A1A (CW) si (optional) FSK

Memorii presetabile: 4 + 1

Receptor: IF1 40.9MHz, IF2 9.91 MHz

Emitator: IF1 9.91 MHz

Stabilitate in frecventa: Sinteza de frecventa, 1ppm @-20/50^oC, 2ppm @ -40/-20^oC

Supresie armonici: >50db fata de PEP

Suprimarea purtatoarei: > 40db fata de PEP

Rejectia frecventei imagine: >80db

AGC: +/- 2db maxim pentru 1uV la 1V input

S/N 12db SINAD J3E:  1uV

S/N 18 db SINAD A1A: 1uV

ANL (limtator de zgomot) automat

BFO pentru A1A: 1000 Hz, fix

Anul acesta, shack-ul meu s-a upgradat cu o statie pentru HF, militara - tip “manpack”, pe care intentionez sa o utilizez in regim portabil in locul batranului IC-703+ care tot sufera varii experiente fumegatoare, semn ca se doreste pensionat.

Cum propagarea nu este tocmai buna pentru QRP ( La Ham Fair 2017 care a avut loc in Friderichshaffen am pus ochii pe o statie germana (cum altfel?) AEG SE6861/12mod.
Verde, nou nouta, cu toate accesoriile necesare. Ba chiar am avut ocazia sa o si testez la fata locului…

DESCRIERE

SE6861 este o statie proiectata in anul 1976 la AEG-Telefunken in Ulm, de catre o echipa din care au facut parte: Ulrich L. Rohde (N1UL/DJ2LR), Klaus Eichel (DL6SES) si Peter Suelzer, (DF9FJ). Asadar, nu numai ca este o statie militara HF excelenta dar are si un pedigree deosebit!

Potrivit “legendei”, proiectul acestui transceiver s-a nascut cand cei trei se aflau intr-o vacanta la schi si au ramas inzapeziti intr-o statiune din Italia.

SE6861 a trecut o proba “de foc” si mediu ostil in expeditia din anul 1979 a alpinistului Reinhard Messner care a urcat pe varful K2 fara oxigen si abordand o noua ruta (Magic Line) si, chiar daca pe parcurs a schimbat traseul, cele trei statii furnizate de AEG Telefunken (plus panouri solare pentru incarcare) si-au facut treaba si astazi au o valoare “de piata” de circa 100.000 EUR!

Pe langa simplitatea in operare, care nu necesita o instruire prealabila a operatorului, cateva “detalii” fac din SE6861 o statie HF care poate fi folosita in traficul de radioamator fara nicio “rusine”!

La emisie, semnalul de la microfon trece printr-un procesor de voce care adauga cativa db la semnalul perceput de corespondent; receptia este cu dubla schimbare de frecventa, selectivitatea fiind asigurata de doua filtre cu cristal: 8 kHz passband la IF1 si 2.4 kHz la IF2.
Exista un selector de antene care permite utilizarea unei antene baston sau a oricarui tip de antena filara (AEG recomanda antena tip “dublet”) dar exista si o iesire pe conector standard BNC cu impedanta de 50 Ohm pentru iesire pe cablu coaxial in antena sau intr-un amplificator extern. Foarte avantajos, transceiverul poate opera atat in USB cat si in LSB, un avantaj fata de alte statii militare care au posibilitatea de a lucra doar intr-unul din aceste moduri, necesitand modificari substantiale pentru a le avea pe amandoua!

Selectarea frecventelor se face cu comutatoare decadice operate prin apasarea de butoane pentru Up/Down, frecventa fiind afisata prin mici ferestre in dreptul fiecarui comutator. Spre deosebire de alte modele militare care folosesc acelasi sistem, comutatoarele permit setarea in ambele directii si nu numai intr-una.

Tunerul automat realizeaza acordul antenelor baston si al antenelor filare pentru un SWR de maxim 1.5 in circa 2-3 secunde, fiind controlat de microprocesor; acordul are loc dupa schimbarea frecventei, la prima apasare pe PTT. Sistemul verifica apoi mentinerea acordului la fiecare intrare in emisie, efectuand, daca este necesar, un nou acord. Pentru usurinta in operarea in teren, se pot memora 4 frecvente care, impreuna cu frecventa afisata, reprezinta 5 canale de “memorie”.

Nu in ultimul rand, dimensiunile compacte si consumul redus de energie o fac potrivita pentru operarea din baterii (incorporate) in regim HF portabil in activitati SOTA sau WFF.

Printre dezavantajele care vin “la pachet” as mentiona faptul ca necesita alimentare la o tensiune atipica (24-36V) si conectorii speciali pentru alimentarea externa si accesorii (casti/microfon si cheie CW) dar, in cazul meu am primit impreuna cu statia un set de conectori asa ca nu imi fac mari probleme.

La emisia in CW, prima apasare pe cheie trece statia in emisie trecand apoi pe receptie dupa 0.7 secunde dupa ultimul semn transmis, fiind posibila astfel operarea SEMI-BK. Nu sunt un operator de CW dar cred ca aceasta procedura, de a da un punct inainte de a transmite creeaza un oarecare disconfort daca se doreste operarea in vreun concurs ;-)

In ceea ce priveste alimentarea cu energie electrica, statia este destul de versatila, avand un bac de baterii care contine si electronica necesara incarcarii si stabilizarii tensiunii de 14.4 V necesara pentru modulele interne.
Exista diverse optiuni de alimentare: doua pack-uri NiCd sau NiMh de 15V (12 celule x 1.25V) sau un pack de 24V ori  pack LiIon de 36V/30Ah precum si optiunea de baterii de unica folosinta.

Exemplarul meu nu a avut antena originala ci o antena produsa de Hughes (AS1887) pentru PRC-74B. Intrucat antena si statia au montura tip “surub” pas Witfort de 3/8, am folosit o mufa din alama (echipamentul a fost “livrat” cu un “T” din fier), cumparata de la “raionul” de instalatii J.

Capac peste toate, statia este “waterproof”, AEG jurandu-se ca poate rezista in imersiune la 1m pentru cel putin o ora…

Statia nu a sosit cu rucsacul original dar, la un alt stand am vazut un rucsac pentru statii Harris despre care proprietarul nu stia ca e de vanzare si, pentru pretul corect, SE6861 si-a gasit si modalitatea de transport :-) .

OPERAREA

Este simpla si presupune trecerea selectorului de memorii pe “0”, selectarea tipului de antena si pornirea statiei. Se alege frecventa de lucru si se apasa PTT pentru realizarea acordului, daca se foloseste antena filara sau cea baston. Se recomanda ca la fiecare schimbare de frecventa sa se apese PTT pentru efectuarea acordului de catre ATU.

Nivelul audio la receptie se alege si el, tot cu un comutator tip decadic, dar cu doar 7 pozitii, nefiind posibila oprirea completa a semnalului de receptie. Pe panoul frontal exista doi conectori, in paralel, pentru conectarea a doua seturi de accesorii (casti-microfon, microfon, difuzor, cheie CW sau EMU/crypto).

Pe timp de noapte, inscriptiile de pe comutatoarele decadice sunt retro-iluminate in oranj la apasarea unui buton aflat pe selectorul de antena. Pentru observarea functionarii corecte, exista un LED verde care lumineaza in ritmul modulatiei  incepand de la circa 20% PEP si un alt LED care semnalizeaza descarcarea bateriei. La aprinderea acestui LED, statia mai poate fi operata pentru foarte scurt timp si doar pe putere redusa.

In lateralul bacului de baterii, exista un LED portocaliu care semnalizeaza incarcarea acumulatorilor.

Pentru a simplifica operarea in conditii dificile, selectorul de frecventa este protejat de un capac metalic pe care exista o eticheta ce permite notarea frecventelor presetate cu un marker sau un creion. Materialul etichetei permite stergerea si rescrierea adnotarilor.

M-am jucat cu ea si, la o prima chemare in 20m a raspuns o statie IZ. Tot in 20m am reusit sa lucrez OD5VB prin pile-up!

Am primit rapoarte OK despre modulatie; un pic metalica dar “plina”, efect al procesorului de voce!

Din informatiile prezente pe internet, o astfel de statie a costat armata Vest-

Germana peste 14.000 DM!

Greutatea unitatii radio este de circa 4 kg iar impreuna cu unitatea de acumulatori totalizeaza circa 8 kg.
Rucsacul este de la statia HARRIS FALCON II, model "Radio Ranger", pur militar, extra rezistent si judicios compartimentat.

Proiectata de: Rohde-Schwartz
ATU: AEG Siemens
Productie de serie: AEG-Telefunken


Mai jos sunt cateva imagini si un scurt videoclip.

Detalii si aici.

Dipol VHF (UHF) simplu

M-a intrebat un amic ce antena de VHF sa isi faca. Imediat m-am gandit la un dipol deschis, ca varianta optima eficienta/pret.

Ca materiale, am folosit o teava din aluminiu, de 20mm grosime in lungime de 1m si o bara de PVC, tot de 1m lungime precum si o mica platbanda de circa 25mm latime si 1mm grosime in lungime de circa 45mm.

Pentru inceput, am facut suportul (consola) din PVC. Am taiat din bara de PVC o lungime de 30cm si am marcat-o la jumatate. Pe aceasta bucata se vor prinde elementele dipolului.

Restul de circa 70 cm urmeaza sa fie "consola"; la unul din capete am prelucrat-o cu un Dremel astfel incat sa fie concava si sa se imbine pe generatoarea bucatii de 30 cm. 

Am pregatit o mica cantitate de rasina epoxidica cu intarire rapida, am imbinat cele doua bucati si le-am prins cu un holtzsurub.

Apoi, am taiat in doua bucati de cate 50 cm teava de aluminiu si am realizat gaurile de prindere cu o bormasina cu coloana pentru a asigura perpendicularitatea pe generatoarea tevii.

Cele doua bucati de teava de aluminiu se introduc pe bratele suportului in forma de "T" din PVC apoi gaurim si PVC-ul pe tiparul gaurilor din tevile de aluminiu.

Din bucata de platbanda am facut suportul mufei BNC mama cu flansa patrata. Aceasta se prinde cu un surub M4 pe una din tevi, pe gaura realizata la 7mm de capatul tevii. Firul central al mufei se conecteaza la cealalta teava, tot la prima gaura.

Antena se realizeaza in circa o ora cu un cost total, circa 30 lei...

Bratul consolei (circa 70 cm)  asigura instalarea la distanta de cel putin 50 cm (L/4) de un pilon. Atentie insa, pe directia pilonului, diagrama va fi cardioida cu o atenuare de circa 3 db!

Masuratoarea de SWR arata 1:1.2 in banda 118-138 si circa 1:1.5-1:1.6 in 140-146 MHz cu 1:1.6 in 435 MHz, apropiat de simularea in MMANA:

Pentru un acord perfect in 145 MHz, lungimea celor doua elemente ale antenei trebuie redusa la circa 49 - 49.3 cm. Eu le-am pastrat de 50 cm pentru banda aero.

Cum arata antena:

Este pusa cu GND in jos :-) dar merge la fel si invers :-)))

IF tap for external SDR on a Yaesu FT-840

So, a fellow ham (YO6FPW) has send me his radio to repair and for a very interesting mod!
He want to be able to use his RTL-SDR receiver with this radio.
The repair was nothing interesting. The Rx/Tx relay was fried and the RS signal was not present on the first batch of switching diodes.
The relay was changed with a similar one and the fried PCB was repaired with a wire directly from the Toshiba high current driver.
On the other hand, the asked mod was a real challenge!
The first IF on this radio is on 47.055 MHz so it's suitable to use it with a low cost RTL SDR but the signal is very low before the crystal filter. It's better to have the signal tapped before the filter. Why? Well, the answer it's obvious: to have a whole 2 MHz to enjoy!

So, first, I tried to use the G4HUP schematics (PAT)  but it didn;t work as expected. The signal was very low, maybe because I tapped the IF signal from a different point or maybe because my J310 are fake :-).

This is where I put the IF tap:

It's a low impedance, low signal point so I needed a good RF preamplifier.
Listening with a RTL-SDR produced usable signals only on strong signals so I was looking in my little boxes after some suitable components. I remembered that I have somewhere some Analog Devices AD8008 for a "never started project" and I decided that this is my path!

So, I quickly draw a schematic, I also drawed on a PCB and put it to work.

Here is the schematic, based on the application note from Analog:

Everything was in SMD because I was looking for a small footprint, but the result was nice (at least for what I needed:

I also found some metal sheet to made a custom shield case.

I didn't save the results from the IFR sweep analyser; the amplification is around 12 db at 5V and is very flat, which is what I was looking for! At 9 V, the amplification is around 17 db! Good to know!

The 5V for powering the amplifier is taken directly from the Q1034 on the SMD side of the "RF" PCB board. I didn't took it from L 1012 as is shown on the G4HUP page because there was some problems with that path and I didn't want to stress the PCB. So I took the 5V directly from the TD6278P SMD circuit (Q1034), on pin 12 (RS).
This 5V is present when the radio is on receive only and when transmitting is 0V so the preamp is protected from accidental high RF at input.

As for the output, I had a nice BNC connector with a small RG316 cable, just asking to be on the rear side of the Yaesu FT-840!

This is the final work:

And here is a small youtube movie with the SDR at work:

Kenwood AT-300 ATU to ICOM Radio - II

In a previous post I wrote about a devil plan to connect a Kenwood AT-300 Automatic antenna tuner to an ICOM 7300 radio.

Here is the connection diagram (again, by hand) and the final iteration of the code.

Later edit:

This is the final look after some work on a test PCB. I let the USB port accesible for future development:

Kenwood AT-300 ATU to ICOM Radio - I

Well, I have a Kenwood Automatic antenna tuner AT-300 and some ICOM Radios (IC-7300 and IC-703+) and I want to use them.
I tried to find on internet something already made but no chance. Looks like the Kenwood AT-300 is very rare or the fellow hams are using it as is intended, with a Kenwood radio.

It's not my case so, after a couple of years of thinking, I put myself together and I start to explore the possible solutions to connect the ATU to my IC-7300 radio.

First, the radio has a START and a KEY line and the "0" logic is +5V and the '1" logic is 0V. Same as the AT-300 which is good. The Kenwood AT-300 has the same voltage logic but the signals are TS and TT.

Basically, the Kenwood tuning procedure is:
-The TUNE on the radio is pressed
-The radio pulls down the TS line AND start transmitting around 10W CW.
-The AT-300 respond by pulling the TT down after about 100 msec. ONLY IF RF IS PRESENT.
-If a tuning solution is found, the tuning stops and the TS line is pulled up to 5V.
-After 15 seconds, the radio stops the RF and pulls up the TS.
-If the TT is still up, the radio return TUNING ERROR. If the TT pulls up BEFORE the TS, the radio show TUNED.

For bypass, the TS is pulled down  for 500 msec. WITHOUT RF. To put the tuner in circuit, repeat this sequence.

The ICOM radios, have a slighty different "tuning protocol":

-The radio pulls down the START line.
-The tuner pulls down the KEY, causing the radio to transmit 10 W CW
-If the tuner found a tuning solution, the KEY is pulled up. From what I found using the Codan 9350 antenna, there is no time limit for keying the radio!
-If there is no tuning solution, the KEY is pulled up, then down for 70 msec.  and then up again (and rest up).

The solution seems that is to "alter" the KEY and TS sequence with a microcontroller (Arduino).
Something like this:

-Press TUNE on the radio
-The radio pull down START
-The uC detect the START and pull down TS
-uC pull down KEY to transmit 10W CW
-uC monitors TT and pull up the KEY if the TT goes UP.
-If TT is still down after 15 seconds, the uC execute "TUNE FAIL" sequence as expected by ICOM radios.

Already made the test board. initially i thought to put some optocouplers for TS/TT and START KEY but after monitoring the voltages I saw no problem to connect them directly to the Arduino digital ports (max 5V). Of course, the signal lines are connected through some 470 nH inductors and the uC pins have 10 nF capacitors to the ground.

I believe this interface will be good to use it also on IC-7000 (have one and i will test it) and IC-7100.

Stay "tuned" for the next step!

73 de Adrian YO3HJV

LATER EDIT

Here is the first version of the code. Simple tuning, start and stops at the TUNE command from the Radio front panel command.

About the hardware:
The lines are directly connected to the Arduino board and the lines from the ICOM radios are tied up to +5V with 4k7 resistors in order for the radio to "see" the external ATU!
Be aware that, if the output power is not set to be between 5-15W, the radio will turne to the INTERNAL ATU instead of the external, even with the lines pulled UP!