As an Amateur Radio operator I've always had an interest in military radios and communications. In particular I've had a long interest in fully self-contained backpack transceivers that can operate on the Amateur Radio HF (high frequency) spectrum. If you are a radio guy and you spent any time in the military you just see things that catch your eye. For most of my Army career (1979 - 2002) the ubiquitous small unit radio was the AN/PRC-77. We used this iconic Vietnam-era backpack radio for everything; if you had to go run a rifle range, control a convoy, set up a drop zone, chase Iraqis around the desert or run a guard mount you grabbed a couple of 'prick-77's', some spare batteries, and moved out. While these radios had limited performance (their transmission range was just a few miles over ground) they were rugged as hell. The radio case was a thick extruded aluminum box that was sealed at the top and bottom, making the unit completely watertight. The radio was heavy as hell, but it was damned near indestructible.
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| AN/PRC-77 manpack radio (from Wikipedia) |
What attracts me to military radios is, I think, the same thing that attracts me to knives, firearms, stoves, backpacks, compasses, etc. Deep down I'm something of a survivalist/prepper. I like things that are rugged, foolproof and will help me and my family get through the worst of times - either a hurricane (don't laugh - Hurricane Irma just paid us a visit) or a nuclear attack (don't laugh - Kim Jong Un claims he's got a hydrogen bomb that he can strap to a missile). For that time when an EMP pulse turns your iPhone into a smoking lump of plastic and glass I want a radio that will keep chugging along.
From an electronic performance standpoint Amateur Radio systems are good - very good. What they are not, with very few exceptions, is rugged, waterproof, self-contained and easy to use while on the move. Many of the small handheld units are pretty tough little devices, but they operate only on the VHF & UHF frequencies (with an occasional unit dropping down into the 'semi-HF' 6-meter band territory). Radios that operate on the HF bands, say 50 mHz and down, tend to be desktop queens. There are niche manufacturers like Codan that make MILSPEC rugged units that can operate in the Amateur Radio HF bands, but those radios are eye-bleedingly expensive.
So this leads us to military surplus radios. Just as armies around the world dump their excess or obsolete vehicles, clothing, tools, weapons, ships and aircraft onto the surplus market, they also occasionally dump obsolete, excess or damaged radio gear. This feeds a small but dedicated group of radio enthusiasts who grab these radios, get them back into operating condition and use them on the Amateur Radio frequencies. But these surplus radios can be hard to find, for a number of reasons. First, military radios tend to be 'low density' items. This means that compared to things like boots, mess kits and pup tents, radios were not issued in great numbers. Next, because of the high development, manufacturing and sustainment costs for communications gear most armies tend to hang on to their radios longer than other systems, and use them right up until the point where they are obsolete and the supply is exhausted. And last, many of these radios get refurbished and sold to other countries under military assistance programs. As a result there are relatively few good condition surplus radios on the market.
This means that good examples of the AN/PRC-77 can be hard to find. As the US pulled them from service starting in the 1980s they were re-furbished and sold in huge numbers to countries like Israel, Australia and Pakistan.
Still, the itch must be scratched. While I've been looking for a good working 'prick-77' for some time I've also kept my eye open for other suitable manpack military radios. A few months ago I got wind that a surplus dealer in Pennsylvania, Coleman's Surplus, was selling complete surplus Czech military radio kits for an amazingly low price. How low? Well I'll just say this - the radios were being sold untested, but the price was so low that it was worth taking the risk and buying sight unseen.
The radio is the RF-10, a fully transistorized manpack radio designed by Tesla Electronics in Czechoslovakia in the 1970's and produced through the 1990's. It was designed to fill the same role as the AN/PRC-77 was filling in US Army units - a short range squad or platoon radio operating in the FM mode near the 50 mHz frequency segment.
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| RF-10 on the right. On the left is my Yaesu FT-817 that was used as a reference transceiver |
Here's the rundown on the radio's capabilities, straight from the RF-10 operations manual:
Frequency Band:
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44.000 to 53.975 MHz
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Channel Spacing:
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25 kHz. All 400 channels are directly selectable using the 3 rotary switches
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Mode:
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Single channel simplex using frequency modulation (FM)
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Transmitter Power
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Nominal Power: 1 W
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Low-transmit Power
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0.1 to 30 mW
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Range:
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1.5 meter whip antenna - 5 km
0.5 meter whip antenna - 1 km
Dipole antenna (3.3 meters) - 10 km
Directional dipole antenna (30 meters) - 20 km
(these are average ranges over moderately wooded terrain)
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Operating Temperature:
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-35℃ to +60℃
The radio set can be operated at reduced efficiency in the temperature range from -50℃ to +70℃
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Power:
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The radio set is powered by a 6 volt DC battery
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Operating time:
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At full charge the battery pack will permit operating for up to 10 hours at a 5:1 listening/transmitting operating ratio
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As you can see, at 6 volts and only 1 watt transmit power it is very low power radio, suitable only for local communications. But that's in line with other military radios of its type. The PRC-77 only puts out between 1 - 2 watts on battery power, and it uses a 15 volt battery. It looks like the RF-10 is a very power-efficient design.
There's some information about the RF-10 on the web in both Czech and English. The Czech site 'Military Radio Station RF-10' does a good job of laying out the radio's operational characteristics and covers some troubleshooting options. The site also provides some interesting shots of the radio circuitry. I was surprised to see some early integrated circuits (labeled 'Tesla') on the boards (Google Chrome does a pretty good job at translating the content). The site PRC68.com has a good page on the RF-10, and it's in English.
The RF-10 is simple to operate. The user sets the frequency using the mHz/kHz/Hz mechanical dials on the front of the radio, attaches the handset and any one of several whip or long wire antennas, switches the radio on and talks. Not much to go wrong or mess up.
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| Front of the RF-10 showing the antenna connection, volume control, frequency dials and handset connector |
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| The RF-10 radio 'set' is stored, transported and deployed in this large Styrofoam container |
Opening up the container you find a complete radio set:
The set consists of:
- RF-10 transceiver
- One handset
- One battery pack
- Carrying pouches for the radio and battery pack
- Carrying straps
- Two whip antennas, very cleverly wound up in the lid of the Styrofoam box for storage/transport
- One long wire antenna
- One dipole antenna
- One documentation packet that includes an instruction manual (for you old Army types, think of it as the -10 manual), a component list and a host of assorted and official looking certifications with lots of stamps and signatures
Virtually all of the components can fit into the radio's carrying bag, and using the supplied straps the bag can be worn over the shoulder or on the back. This makes for a very portable and versatile radio system. With a proper antenna setup, and by choosing your ground carefully, you should be able to communicate 20 miles or so. Remember, this is an FM radio, so you won't get much of the radio wave atmospheric 'skip' that is common with AM or single sideband signals.
The biggest issue with the RF-10 as I received it is the battery pack. The Czechs developed an interesting battery design that utilized five rechargeable D-cell sized NiCad batteries soldered together. The batteries were rated to provide 6 volts at 5 amp hours. The battery pack sits in an aluminum battery case that connects with the main radio via a waterproof electrical connection.
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| The battery case seen connected to the bottom of the RF-10 radio. Note the operating instructions printed on the side of the radio. Not very tactical, but not a bad idea either! |
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| The battery case with the top off showing the battery cell arrangement. Note the leaking batteries. Yuk |
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| The batteries have a 1984 date stamp |
After some thought, and checking some on-line resources, I decided to modify the battery case to accept a modern 6 volt, 3.3 amp hour AGM battery. These small batteries fit just fine in the battery case and are relatively inexpensive (about $15 on Amazon). The modification ended up looking like this:
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| I reused the battery connection sockets and leads from the original NiCad battery pack. It's these sockets that carry voltage to the radio via matching plugs on the inside of the case lid. When closed up the battery case slides on and locks to the bottom of the RF-10 radio (seen here) |
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| The 6 volt AGM battery snuggled down in the battery case just fine. I used some Styrofam pieces to keep the battery from sliding around |
This modification seems to work just fine. I have not 'stress tested' the setup to see just how much operating time I'll get out of the battery, but based on 5:1 listening/transmitting ratio I'm estimating a couple of hours of operation before I have to recharge the battery.
How does the RF-10 perform? To test the radio my friend Bill and I used it on the portion of the 6 meter band (50 - 54 mHz) that US Amateur Radio General and Extra class license holders have access to. Using a modern Yaesu FT-817 transceiver for the other half of the conversation, and testing just short distances across parking lots and city parks, Bill and I discovered that the RF-10 performs very well. The audio quality coming out of the RF-10 is quite good. Not broadcast quality, but certainly what you would expect out of a 1970's - era military radio. There are no other indications of issues and radio seems to be spot on frequency.
So following the prepper mantra of two is one and one is none I decided to order a second RF-10 set from Coleman's. Like the first set, this second could be described as 'new in the box'. The transceiver looked unused and most of the components were still sealed in plastic. Only the battery case looked used - very, very used. But this new radio had some issues. First, the handset was inoperative. I could hear through it, but when transmitting there was no audio coming through to the other radio. The other operator could hear my radio breaking squelch, but no audio. After acquiring a junked handset from a third party I was able to determine the issue was a defective microphone element. A quick swap out of mic elements and the problem was solved. Next, this new transceiver (which has a later production date than my first one) has a very sensitive squelch setting, and the squelch will open up when the radio is around even the slightest RF interference sources. Third, there's a low hum generated by the radio during transmit. Not enough to interfere with communications, but it is annoying. Still, the radio seems to be perfectly serviceable. The battery case got the same modification as the first one, and RF-10 #2 is on the air!
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| Ready to communicate, Comrade! |
So I guess these toys will keep me busy while I continue my search for nice 'prick-77'.
Stay sharp!
Brian
