25 mai 2022

ICOM IC-7100 E Extended frequency Mod

Our EmComm group ( RVSU ) is using  the IC-7100 from ICOM as primary HF Radio.

We therefore must be able to use it on the full range of frequency so we "mod" it. 

Actually, we modified the configuration diode matrix so the radio will TX from 

0.1 MHz - 199.999 MHz and

400 - 470 MHz.

It will still not transmitt AM on the VHF and UHF.


-The modification cand damage your radio!

-Do not transmitt out of the authorisation privileges!

-I have no responsibility for what are YOU doing with YOUR radio.

Pictures are said to worth thousand words, so I give you two thousand:



The removed diodes are soldered on one side of the pads just to have them handy when the mod will be reversed (if needed).

19 mai 2022

ICOM AH-4 Automatic Antenna Tuner modification for RVSU

The Spring is here full power so is the war just North of Romania so our Emergency Communication Team (RVSU) is preparing for... field day!

Our standard in HF EmComms are ICOM radios and ATU's; we are using IC-7100 as our main HF radio paired with T2FD antennas for NVIS and AH-4 with verticals and wires for various Long Range HF.

In this post I will briefly show one modification for the AH-4 Automatic Antenna Tuner (one of the best in my opinion, for 100W output power).

It consist in changing the way the Coaxial RF cable and the Control cable are connected.

Because our concept is based on modular kits, the AH-4 must be able to be installed quick, reliable and we must have provisions to modify the setup if the field conditions required so and this must be done by operators with minimal training.

Disassembly the ATU
The standard ICOM AH-4 box include, among other things, a 10m LMR coaxial cable and 10m of 4 wire control cable terminated with the infamous MOLEX connector present in ICOM HF radios.

The way those cable connect to the Tuner box is pretty against "field use" principles therefore, a solution must be found.

Wiring the AH-4 ATU
After a few years of playing with my own AH-4, I concluded that it is not acceptable to open the case of the tuner anytime the cable must be connected or disconnected.

Another problem is the fixed lenght of the cables. Just 10m might not be enough in certain scenarios and while another coaxial can be added with the help of a female-female adapter, require intimate knowledge from the field operator and present some fatal risks for the integrity of the radio or the ATU if the wires are connected in the wrong way. 

So, another solution must be found!

We are not using the ATU in permanent setup so, some measure originally designed to prevent the water or moisture ingress can be reduced in order to accomodate some that can give more simplicity in installation and use.

First, the RF connector must be moved from inside the ATU to the outer case. 

The SO-239 (UHF-female connector) will be seated just where the cable clamp was. 

The connector is a good quality one, from Amphenol.

Unfortunately, the plastic will not support the mechanichal stress  of the connector so a small plate was cut from a piece of Aluminium.

Then, the ATU's case was prepared to accomodate the SO-239; the backplate was threaded for 3mm screws for better electrical contact.

Everything fits.

The lower left screw is longer. This is because there will be the Ground connection for the small piece of coaxial cable from SO-239 to the ATU's PCB.

This coaxial patch was made from some cable left from GSM sites and I know it can handle easy 100 W up to 100 MHz. So, I prepared it to be used here.

I removed the original piece of metal with the old SO239 and make some scratches on the Ground pad to install the coaxial patch.

I found a little piece of metal, soldered it onto a metal shield and put some heat shrink tube on it to fix the coaxial patch firmly in place:

Looks good and it is the time to take it to the next level: the control cable.

A few words about choosing the right cable:

In the field you need various lenghts of cables. Often those cables are cut, lost, or even forgotten at the base.

The ATU is drawing less than 1 Amp, typical around 200 mA. The control signals are at TTL logical level (5V) and the "protocol" is nothing more than pulling to ground or to +5V so nothing special with this cable must be observed.

Can be a cheap cable and it is desirable to be found easy. Long story short: what if I could use a FTP cable? Well, on my balcony I have an AH-4 which is connected to the radio with this kind of cable and for 2 years performed extremely well.

The problem with my AH-4 is that i modified it very ugly; the female RJ-45 connector is placed on a cut into the case and, believe me, it looks bad! 

In this case, I decided to use something that I already have in my junk box from a never-finished project. A RJ-45 female-male patch cable designed for panel mounting.

I was a little bit nervous because I thought the lenght of the patch cable was not enough to go from the upper case of the ATU to the PCB...

Checked and it was just the right lenght! So, I could start making the square hole from the round one!

... it fits now:

And this how it is. I put some hot glue to seal the holes but I forgot to take pictures...

At the other end of the control cable, a wall RJ-45 connector was tied to a MOLEX ATU connector. Fortunately, I bought some kits a long time ago so I could make it fast.

This is the electrical diagram for the RJ-45-MOLEX adapter:

... and this is how it looks:

Yes, I know, it's horrible but this is what I found at nearest store to me. I promise I will search for other solution but this is it, for now.

Now we can use (almost) any lenght of network UTP cable and (almost) any lenght of coaxial changing them in the field. And, if there is need for the network cable to our applications and no need for HF, we can use the cable for that purpose.

I hope this is an usefull ideea and will inspire other "brave hams"...

73 de YO3HJV, Adrian.

19 aprilie 2022

Heaphones amplifier PAM8610 - Amplificator stereo pentru casti

I have long felt the need for a headphone amplifier that can be connected to various signal sources, stereo or mono.

A few years ago I built one based on a specialized circuit, LA-xxxxx (I forget the code) but it was dependent on the power supply from the socket as it consumed quite a lot and needed a symmetrical power supply.

And the case was a bit big and ugly....

A little while ago I saw an ad for sale for a 10W amplifier based on the Class D circuit, the PAM8610.

This is a modern amplifier intended for use with 10-15W speakers with 8 Ohm impedance.

I remembered that I also have such a module that has been lying around for a while in my junk boxes and I thought I could use it for a headphone amplifier, which can also be used on speakers if needed.

The major problem is that the speakers are driven on each channel by a symmetrical "H" bridge, without a common ground circuit.

For this reason, connecting stereo headphones, which have three wires, becomes problematic.

My first impulse was to search the boxes for two small signal transformers to make the adaptation but laziness won out and I was left staring at the ceiling, comfortably seated on the sofa thinking of a less bulky solution...

I won't go into the details of how amplifiers work in Class D but there is the possibility of making a contrivance to connect common grounded headphones.

The figure below shows the schematic I used successfully and the finished product, encased and powered by a 9V battery type 6F22.

The resistance values are:

R1 - 150 Ohm (two in parallel!)

R2 - 560 Ohm.

All resistors are 0.25W.

To reduce crosstalk it is best to use as equal resistors as possible on the two branches.

The 17-20 mA power consumption in operation, with LED makes it suitable for powering from this type of battery, the amplifier running down to 6.5V, on test.

It sounds great!

De mult timp simt nevoia unui amplificator de casti care sa poata fi conectat la diverse surse de semnal, stereo sau mono.

Acum cativa ani am construit unul bazat pe un circuit specializat, LA-xxxxx (am uitat codul) dar acesta era dependent de alimentarea de la priza intrucat consuma destul de mult si avea nevoie de sursa simetrica pentru alimentare.

Si carcasa era cam mare si urata....

Cu putin timp in urma am vazut un anunt de vanzare pentru un amplificator de 10W bazat pe circuitul in Clasa D, PAM8610.

Acesta este un amplificator modern, destinat a fi utilizat cu boxe de 10-15W cu impedanta de 8 Ohm.

Mi-am adus aminte ca am si eu un astfel de modul care sta de ceva vreme prin cutiile cu troace si m-am gandit ca il pot destina unui amplificator pentru casti si care, la nevoie, poate fi utilizat si pe difuzoare.

Problema majora este ca difuzoarele sunt actionate pe fiecare canal de cate o punte  tip "H", simetric, fara un circuit comun de masa.

Din acest motiv, conectarea castilor stereofonice, care au trei fire, devine problematica.

Primul impuls a fost sa caut in cutii dupa doua transformatoare de semnal mic pentru a face adaptarea dar lenea a invins si am ramas cu ochii in tavan, comod asezat pe canapea gandindu-ma la o solutie mai putin voluminoasa...

Nu intru in detaliile modului de functionare a amplificatoarelor in Clasa D dar exista posibilitatea de a realiza un artificiu pentru a conecta casti cu masa comuna.

In figura de mai jos este prezentata schema pe care am uitilizat-o cu succes precum si produsul finit, incasetat si alimentat dintr-o baterie de 9V tip 6F22.

Valorile rezistentelor, obtinute prin tatonare sunt:

R1 - 150 Ohm (cate doua in paralel!)

R2 - 560 Ohm.

Toate rezistentele sunt de 0.25W.

Pentru reducerea diafoniei este bine sa folosim rezistente cat mai egale pe cele doua ramuri.

Consumul de numai 17-20 mA in functionare, cu tot cu LED il face potrivit pentru alimentarea din acest tip de baterie, amplificatorul functionand pana la 6.5V, pe testare.

Se aude minunat!

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