R-109M (Р-109м) Soviet Field Radio   1 comment

I’m republishing this old post in English, thanks to the outstanding help of my friend Mary Jo Barber, who kindly translated it for me. She is a professional translator, so she can deal with all kind of texts from Spanish to English, even the freakiest ones as you can see 🙂 So if you need anything properly translated, don’t doubt it, you have the link above to contact her. Thanks a lot Mary Jo!!

> Original post in Spanish <


ID plate

R-109M de Aleksandrov Radio Works

Nowadays, we have become accustomed to wireless communication: Wi-Fi at home and at the office and portable personal radios, in the form of mobile phones, in our pockets. Imagine now that nice smartphone you got for Christmas suddenly growing to the size of a small rucksack, weighing 14 kilos and sprouting a 150 cm long antenna; now it makes the mythical Motorola DynaTAC 8000X look like the latest-generation iPhone. Your new “mobile” is now the R-109M and it’s not from Apple or HTC, but from the Aleksandrov Radio Works. It was made throughout the 70s in a place called Voronezh in a country called the Soviet Union. Thousands of Russian soldiers suffered having to carry it on their backs, along with the rest of their kit.

R-109M front view

Welcome to the past!

Comparing it with one of today’s mobile phones is not altogether accurate, but it gives an idea of how communications and miniaturisation have advanced over the past 40-50 years. The R-109M is a Soviet field radio, or transceiver (portmanteau of transmitter-receiver), conceived for military communications between companies or battalions. It uses simplex mode frequency modulation (FM) (in other words, it cannot transmit and receive simultaneously), with an output power of 1 watt, and works as an independent communication unit – in other words, it does not need a network of base stations and fixed antenna to work, as mobile phones do.

A better comparison would be with walkie-talkies or ham radio. As it happens, we will see below whether we it can be used to communicate with modern radios.

The R-109M is one of a family of field radios, having the R-105M and R-108M as siblings. The only difference between the three is the range of frequencies covered by each model, each being assigned to a different type of military unit. Apart from that, they look identical.

  • R-105M: 36.0 – 46.1 MHz, used by infantry units
  • R-108M: 28.0 – 36.5 MHz, used by artillery units
  • R-109M: 21.5 – 28.5 MHz, used by anti-air units.

In appearance, they are rough and primitive, even for their times. Like many other appliances manufactured in the Soviet Union, they now look retrofuturistic or even steampunk. It’s no surprise that they look outdated, as the original design dates back to WWII, when the Russians used captured German radios as the basis for their own models back in the 1950s. Over the years the technology improved, first with the “D” series (metallic casing and notably larger) in the 1960s, up to the “M” series, the latest and most advanced of these radios, in the 1970s. This one uses vacuum micro-tubes and even transistors in some of its parts, so reducing its size with regard to earlier models.

The voltmeter indicates the charge in the batteries

The voltmeter indicates the charge in the batteries

The radio itself is a type of Bakelite briefcase with a pair of clasps at either end and lots of fittings and connectors. After opening the clasps, on one side we find the instrument panel and, on the other, the battery compartment. The front panel is as analogue as it gets, with a nice array of dials, switches, knobs and buttons. At top left there is a voltmeter, which gauges the level of the battery by measuring the volts supplied: beneath a certain level the radio does not work properly and the batteries need to be recharged or replaced. To carry on the mobile phone analogy, this is the equivalent to the icon that says how much battery you have left.

The rest of the components are used to operate the radio in a range of configurations, antenna type, etc. Of particular note are the frequency controls – a central dial that can be turned to select the frequency, and the dial viewer, an odd circular rubber protuberance to the left of the wheel. A magnifying lens shows the dial and the frequency marks in miniature. I imagine that this system was a very accurate way of selecting the frequency, as operation is totally manual.

The dial viewer

The dial viewer

The radio operator spoke either through a earphone and microphone set or using a very cool telephone handset, the kind that makes you want to order a good air strike as soon as you pick it up 🙂 They both have the same type of pin that can be plugged into either the front or the top of the radio, where there is also a connector so that the radio can be used when closed, for example when being carried on the operator’s back. On the top there is also a connection for the different types of antenna.

R-109M and UM-2 amplifier ready for inspection

R-109M and UM-2 amplifier ready for inspection

Testing, 1, 2, 3

When I first got interested in these Soviet radios, I was specifically on the lookout for the R-109M for one reason: its frequency spectrum covers the range used by Citizen Band radios. The idea was to find out whether it would be possible to communicate with modern radio stations and find a practical use for it, beyond just collecting. I know little about the world of radio, but I do know that modern radios use modulation techniques with names like Single-Side Band (SSB) and similar, which may not be compatible with this dinosaur.

Fortunately, there is a massive community of radio aficionados out there, with a long and solid history dating back to the early days of the discovery and use of electromagnetic waves. Internet is obviously a great ally, offering abundant information and the most specific details about even the rarest and oldest sets.

Logically, the first thing to do is to check whether it at least switches on when it is connected to a power supply. If not, it’s going to be quite a challenge to listen or speak to anyone. The R-109M, conceived for the battlefield, has no type of AC plug and works using 2NKP-20U2 (2НКП-20У2) or 2NKP-24M (2НКП-24М) nickel-cadmium wet-cell batteries. Making this type of battery work is a challenge and I’ll give details below. Right now I’ll just say that initially I was at least able to use them for long enough to conduct the first tests.

Battery 2НКП-20У2

2НКП-20У2 nickel cadmium battery 2.4 v 20 Ah

I was able to verify that, with the right voltage (approximately 4.2 to 5.5 V), the radio switches on and static can be heard through the earphones. Now we can try to tune into a station. However, this isn’t going to be easy inside a building in a big city, and probably won’t be successful. Apart from that, since mobile phones became widespread, very few people use CB radio anymore. I picked up some commercial radio stations very faintly, so faintly as to barely be able to identify them. I imagine that this is due to some kind of “reflection” or something, because, although this radio uses FM, the range of frequencies it covers is very different to the ranges used by commercial radio stations.

Luckily, I got a loan of a modern CB set. The Yaesu FT-747GX, produced in the 1990s, is quite a powerful radio with an output of 100W (25W in AM). With the right kind of aerial, it can be used to communicate with people right around the world (and before TDT, to create interferences with your neighbours’ TV sets). It covers the frequencies reserved for CB and many more. In comparison, the miserable 1W output of the R-109M makes it look like a poor relation, but whatever; apart from the age difference, they were conceived for quite different circumstances.

In any case, it is more than sufficient for our purpose: to test communications between the Soviet radio and a modern set and find out whether we could use the old R-109M like a CB set… but a really cool one 😀 For the moment, we will be happy if it transmits from one room to another.

Well then, the test was positive … though incomplete. It turns out that while the older set works in FM, the newer one has multiple transmission and modulation modes … except FM. This means we would need to add an extra module, which can be found on eBay and the like for about €100. A bit over our budget.

Even so, we managed to establish contact using amplitude modulation (AM) on the Yaesu. As I am a total beginner in these matters, I didn’t even know that this was possible, or why, but it works. Obviously, as we used different modulation modes, the quality was hardly optimal and we have yet to see over what distance we could maintain communication. But it is possible to communicate and, most importantly, we verified that our Soviet comrade is in good health and is not just a lump of plastic and metal to be put on a shelf.

What’s more, this circumstance throws up a new possibility – if the FM module is too expensive, could I not build one myself? A very interesting project, but one for another day 😀

Charging the batteries

Now that we know almost for certain that the radio works (though we still need to test it with another FM set), wouldn’t it be great to take it out into the countryside to listen in to other stations or try to communicate over greater distances? The transmitter power is quite low, 1 watt. With the Kulikow 1.5m omnidirectional antenna, this should give us a range of 6-8 kilometres. Almost any affordable walkie-talkie is twice as powerful and fits in the palm of your hand. Fortunately, I also have a 1968 “portable” UM-2 (УМ-2) amplifier, for use together with this family of radios. Apart from that, there are different types of antennae that can be connected, and with the 40 metre (!) dipole directional antenna that also comes in the pack, we are ready to try something a bit more ambitious 😀

Checking the batteries

Checking the batteries

The real problem is with the batteries. Obviously, they are not the type of battery we are used to seeing nowadays. Neither is it an easy task to mod the set to make it work with ordinary batteries, like we did with the DP-5V. This set uses wet cell batteries of a size and voltage and with connections totally unlike anything we might have lying around the house. What is more, of the several batteries that came with the set, the most modern is from 1987 and the oldest … from 1968! We all know that the battery is normally the first element to start failing in phones and other modern appliances – would it even be possible to use the original batteries, more than 25 years old?

Wet cell batteries have to be filed with an electrolyte, a solution of chemical elements in distilled water which, in conjunction with the metal plates, allow electricity to accumulate (for this reason, they are also known as accumulators). When they arrived, the batteries were totally dry and empty, and looked like they had been that way for some time. In any case, shipping them full would be dangerous (and quite possibly illegal): the electrolyte is highly corrosive and any leak could cause serious damage. Wet-cell batteries are not hermetically sealed, but have openings through which to top up the electrolyte when it is lost or spent. The only fastening is a set of screws and rubber seals.

The radio came along with a ZU-3 (ЗУ-3) charger, supposedly the right type for the batteries included in the pack. Even when they were dry, I could see that a small residual voltage remained, giving a glimmer of hope that they could be recovered. I then tried to connect them to the charger empty; after a few hours, the multimeter was up to approximately 2.4 volts, the nominal voltage for the accumulators. I even performed a first switching on test, which was positive. Logically, however, after a few minutes the charge dropped drastically and I couldn’t use them any longer.

ЗУ-3 Charger

ЗУ-3 Charger. Some contraption.

As I mentioned already, you can find almost anything on the internet, particularly for a hobby that has been on the go as long as amateur radio. With such a vast subject matter, we can find sub-groups specialised in antique radios, military radios and both. As it happens, I found a document that gives the exact formula for the electrolyte for my batteries on the website of the Vintage and Military Amateur Radio Society. As if made to order 😀

204gr KOH + 20gr LiOH + 750ml H2O

The document in question gives details on how to make up the solution, precautions to be taken, instructions on constructing a circuit to make a radio like this work using a PC power supply, and even on how to make your own charger. What more could you want? I acquired potassium hydroxide and the lithium hydroxide, followed the instructions to make a litre of electrolyte, filled the batteries very carefully (using goggles, a face mask and gloves, in a clear, well-ventilated space), and left the accumulators to charge for approximately 8 hours.

Apart from the protective equipment, I also used a measuring cup to measure the volume of water, a 1g precision digital scale, a sturdy plastic bottle, with cap, to hold and store the liquid, a plastic spoon to handle the chemicals, a small funnel and a stainless steel pot and stirrer. Most of these things I had around the house, and those I didn’t I got from a nearby hardware store. It’s probably not as accurate as proper laboratory equipment, but that is hardly necessary and, in any case, I am trying to keep expenses down… it’s probably best to have a good measuring cup, as the typical kitchen kind, with marks for rice, water, sugar, etc., is not really ideal.


Nothing illegal going on here. Honest.

I got the chemicals from a specialised drugstore. Potassium hydroxide or caustic potash is cheap and quite easy to obtain, being used to make soap among other things. Lithium hydroxide, however, is neither cheap nor easily obtainable and I had to order it. However, it is not strictly necessary – it helps to improve performance, but can just as easily be left out. Once we have all the materials and equipment together, the idea now is to obtain a solution with a density of 1.16 g/ml. According to the instructions, we get this by adding 204 g caustic potash to 750 ml distilled water; if we are using lithium hydroxide add 20 g and, lastly, add water to bring it up to one litre. The chemicals should always be added to the water, not the other way around, and little by little. Otherwise, the reaction may be violent and splash everywhere, and we don’t what that to happen. The potassium hydroxide, particularly, should be added in tiny amounts and stirred carefully. The water and the container will heat up with the effect of the chemical reaction, and may even burn. Obviously, avoid inhaling the fumes and coming into contact with the liquid (especially on the mucous membranes), as they are toxic (this is why we use gloves, masks, goggles and protective clothing). Don’t even dream of drinking it!

Basically, it’s about taking normal precautions and being careful, but there is no need to be scared either. It’s not going to explode or suffocate us with fumes … just wear a mask and keep your nose out of the mixture. Don’t sniff the chemicals or pick them up in your hands – no playing around, in other words. I would recommend not doing this in the kitchen or anywhere else full of appliances, and using stable, flat-based containers – not to be used afterwards for cooking or other chores! I wouldn’t even vouch for their safety after washing them well.

This stage of the process is practically the same as making soap. For more details and handy tips, google for cold process soap making.

So now, the electrolyte is ready. Very carefully and using the funnel, pour the liquid little by little through the corresponding opening. Each battery has two, as they are really two 1.2V cells, soldered together and connected in series. The liquid should fully cover the internal plates that you can see through the hole, but not reach right to the top. I would recommend letting the liquid soak in well before beginning to charge the batteries, and leaving the caps off. This is important! Because of the electrochemical process, the liquid often expands and spills over. If the cap is left on, the pressure can cause it to leak out through the seals around the terminals and the battery can be ruined. For this same reason, it is also a good idea to place the battery in a hard plastic container, so that the table and other elements are not damaged if there is a leak. If the tops of the internal plates are exposed after a leak, add more to cover them again.

In spite of the time and money invested in making the electrolyte, the results were not very encouraging at first. I did get the R-109M to work for a while longer, but only for 45 minutes to an hour… enough to try to pick up a signal or test it with another CB radio and to check its capacity, but no more. Not enough to take it out into the country or try long distance communications. After this time, the voltmeter needle plunged to below the 4.5 volt mark and the quality of the reception was immediately affected, to the extent that not even background static could be heard. In optimal conditions, these batteries can last from 12 to 17 hours.

A bit of a disappointment. Had I mixed the electrolyte correctly? More than once a few drops had splashed out onto the table, or I came into contact with it when I cleaned up spills without gloves… and it wasn’t half as corrosive as I expected (mind you, I’m not saying it’s not dangerous or you shouldn’t be careful… it’s still toxic, after all), so maybe the solution was too weak. Or was the problem with the charger? The output shown on the ammeter when I charged the batteries was much lower than recommended for these batteries (4 amperes over 6 hours). After much searching, I eventually found a copy of the original ZU-3 manual in DjVu format and, with patience and Google translator, I discovered that this charger was originally conceived for other kinds of batteries, quite unlike those used in the R-109M.

Or maybe I can’t simply expect 30- or 40-year-old batteries to work at even a fraction of their original yield…

The charger had me quite cheesed off. I even left the batteries charging for two full days, with no improvement. I suppose that if I knew more about these things I would have realised immediately, but the only way to check was to find the right kind of charger, or to build one myself using the instructions from the document I found on the internet.

Charging the batteries with a regulated power source

Now we’re talking!

The solution came thanks to the Yaesu FT-747 set that I had borrowed … or actually from its power supply, a massive heavy thing, bigger than the radio itself, but with one important characteristic – it can be regulated, meaning that the output voltage and amperes can be adjusted. Great! I left the batteries charging at 4 amperes over eight hours, and it works! For my first test, the radio stayed on (not transmitting for the moment, just receiving) for 10 straight hours, and the voltmeter needle remained well in the operative region afterwards.

So now I’m ready to use my old communist radio all around the world… who knows what strange contacts I might make! It’s a matter of getting out there and finding out 😀 Meanwhile, after so much talk about radios, I’ll say goodbye with this:





Publicado 9 septiembre, 2015 por bravido en Cold War, Collecting, Militaria

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