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Investigating the PRR (Personal Role Radio), a transceiver used by the British military.

JP3DOI Junichi Masaki (translated by JI1GYO Grace Wang)


The PRR (Personal Role Radio) is a spread spectrum digital transceiver that the British military has been using even now for communication between soldiers. The radio operates in the 2.4GHz band, transmitting output in 50mW on 16 out of 256 usable channels. The radio body is made of reinforced resin, and neither a microphone nor speaker is built-in. To communicate, a specific type of headset is required.

PRR (Personal Role Radio) is literally a radio for personal use. It was originally designed by an Italian manufacturer Marconi Selenia Communications, who is currently a part of Leonardo S.p.A., a company that specializes in the area of defense and aerospace.
※ The radio that used for this study is made by Selex communications.

This article is to introduce this very interesting and rare type of radio. I have obtained two of the transceivers in brand-new condition. Unfortunately, I was not able to check the circuit board inside because the device body is tightly glued together and not able to take apart.

A low power transceiver specific for military use


There is an article that explains about PRR on the official website of the British Army, which is mainly quoted from the manufacturer, Leonardo S.p.A. website.


British Army official website

Summary:
Personal Role Radio (PRR) is a portable radio transceiver for soldiers to communicate for short distances.。
It allows communications even across walls or other obstacles, thus it enables a commander to deliver immediate orders under various circumstances on the battlefield, for example, encountering enemies or sudden situations, to increase army effective battle power.
As a communication devise, it is effective, works well for soldiers who move around frequently, and is durable in harsh environments.
General speaking, PRR provides functions for soldiers on the front line to communicate and effectively delivering command orders.
It gives a huge contribution for battle efficiency.

Specifications:
・Frequency: 2.4GHz Band
・Output: 50mW
・Power supply: AA battery x 2
・Battery life: over 24 hours (transmitting/receiving/listening=1:7:16)
・Communication range: Prospectively 500m (approximately a range of 3 floors in a building.)
・Transmitting method: Simplex
・Number of channels: 16 of a possible 256
・External dimensions: 140L×85W×25H mm (not include antenna)
・Weight: Approx. 250g (not include battery)

According to the official specifications, the performance seems to be that of a license free low power transceiver, but since it uses the 2.4GHz band, it may be closer to a Bluetooth intercom used for bike touring.

How to operate

Despite of the output power being only 50mW, the PRR operates up to 500 meters on the 2.4GHz band. This performance is hugely different than the average military VHF low band portable radios. Now, we shall move on checking the details of how to operate it.

Army soldiers usually act in group; to reduce the possible damage when being attacked, soldiers move away from each other, or depending on the situation, spread far apart. PRR allows normal conversations between soldiers without having to speak louder in such circumstances. Also, it solves the problems of being difficult to hear each other when surrounded by loud noises.


Soldiers move away from each other.


Soldiers spread apart in an alert.

Nonetheless, circumstances of when sneak on into a building where the enemy soldiers are hiding,communicating in loud voices compromises positions and intentions. With PRR radios, speaking in only a low voice is enough to communicate with each other, even across floors or through walls.


Communications in loud speaking voice compromise positions and intentions to the enemy.

Communications are not encrypted

Since PRR is a digital radio transceiver for military, it is assumed to be equipped with encryption for communications, however, it is not. The reason is not only the transmitting range is within 500m, which is considering rather short, but also, the spectrum is a difficult type to be eavesdropped on to start with, on top of that, it is designed as a spread spectrum type device, which makes harder to be intercepted, so encryption thus was determined to be unnecessary. Moreover, PRR is not designated to be used for communications between the army front line and headquarters where there might be conversations highly possibly involving strategic planning. PRR is only to be used for communications between soldiers, and the information contained in those communications are not crucial and are to be "consumed" in a short period of time.

However, the newest version of PRR seems to be equipped with encryption. If this is true, the old version PRR radios like the ones that I have, which have no confidentiality performance, may have become surplus items in the flea markets already.

Operation


Antenna
The frequencies used are in the 2.4GHz band, but the antenna only measures 6cm long. I suspect there could be an internal sleeve antenna that acts like a vertical dipole. Its pin is SMA which is same as LAN.


Headset connector
Connecting headset through a 5-pin connector, a type of pin connector perhaps no one has seen. For your information, this connector is called a “LEMO connector”, and has been used in aviation, aerospace and the military due to its high reliability.



The connector has high reliability and is produced by LEMO Corp. of Switzerland. According to the information found on the website, it costs ¥4,000 (about 36USD) for just one plug.


Connector characteristics: (Left) hold on to the sleeve and pull to remove the cable from the connector. (Right) holding and pulling on just the cable will not remove it from the connector.

<Digression>
PRR’s appearance is very similar to the Replica, which a device for survival games. When I just received my PRR radio, I almost thought they delivered a Replica instead. Once I took a close look, I was relieved, as the connector is not an average audio one, but a LEMO connector, as well the supplied adapter is for a gas mask.

Power switch/sound volume adjustor
The volume control also functions as a power switch. Turn the control to the right until it makes a click sound, then a high tone alarm is heard from the headset, which indicates that the power is ON. Turn the control all the way to the left until the click sounds, and a low alarm tone confirms power is OFF.


(Left) Power switch/volume control, (Right) Channel selector.

Channel selector
There are 16 channels contained in each 16-channel group, which makes 256 channels in total that can be selected. There is a rotary switch under the attached cover, which is used to select the channel group. More details in this regard are explained below.


Turn the rotary switch to select one of the 16 channels groups that includes the desire channels. Since there is no selective call, all you need to do is to select the same channel of the person you want to speak to.

Battery storage
The chamber to store batteries is in the bottom of the radio and is accessed by opening a cover. There is no seal ring to keep its airtightness, which was not my expectation. It may be designed to keep water out from getting inside the radio, but the batteries certainly are soaked once the radio is submerged.


The battery chamber has no sealing to protect from water intrusion. The cover is also poorly made.

The other thing is, covers usually used for this kind of purpose are attached with a metal shaft, but PRR has only two pieces of protrusions on the resin made lid to connect to the radio body. This structure can easily cause difficulty in closing the cover if these protrusions get bent. In such case, taping it up for urgent use may be necessary. On the other hand, the battery terminals are built-in on the battery lid, so there is nothing that can be done if the cover is lost.

Standard supplied accessories

There is an antenna, a headset, a pouch, a wireless PTT button and a mic adaptor for a gas mask as supplied accessories with the PRR radio, as well an operator’s guide.

Operator’s guide
The name of each part and how to connect it are briefly printed on a piece of coated paper.


Simplified operator’s guide

Dedicated pouch
To store PRR radio device in the suppled pouch for the supposedly best convenient usage during battle. The pouch does not look particularly durable, judging by the cutting and stitching. The radio must be taken out of the pouch to replace the batteries, a design that does not provide satisfactory practicality.


Standard supplied pouch.

In fact, there is another properly made pouch for the device that I got from another source that is surplus from the army. With this pouch, the radio does not need to be taken out from the pouch to replace the batteries.


A more adequate pouch that I got from other source. Easier to replace the batteries.

Headset
Since there is no built-in microphone or speaker, a specific headset is supplied. The headset is set close to the left ear, then fixed in place with a band around the head.


The headset in place

There is a dynamic microphone on the tip of the boom to receive voice audio. Both the front and the back sides of the microphone can pick up noise. The so-called dynamic microphone is constructed with a function so that when the front and back receive the same noise, noise cancellation occurs. The cancellation will not happen when only audio is input to one side (the side close to the mouth). This is the theory that only voice audio will be picked up while in a noisy environment, because noise will be cancelled when simultaneously received into the front and the back of the microphone.


The dynamic microphone that attached on the tip of boom. The boom is not robustly made.

The speaker is padded to cover left ear entirely. However, it is not completely soundproof, and there is small crevice that enables external sound to enter.


The pad that is used to cover the ear. A water-resistant speaker is used.

To prevent too much heat around the head by wearing the headset, the band is made of a mesh fabric material. However, the sewn stitches do not look durable.


The mesh fabric and rubber band are not anything special, only average materials.

The length of the headset cable is nearly 45cm. This enables you to lift the radio higher so the antenna to be at the highest position possible.


The radio in the dedicated pouch and attached to the left chest strap of the battle vest.
※ The vest in the photo is not a British army item.

Adaptor for a gasmask
The adaptor is supplied in case the radio is used with a gas mask. Voice audio becomes muffled across the gasmask, so the adaptor is used to clear up the sound.


Adaptor when using a gasmask. The round part connects to the mask. The square recess part (right) is to insert the microphone.

Wireless PTT button
This is the most outstanding feature of the PRR radio; to transmit by pushing the supplied wireless PTT switch instead of the usual built-in PTT button on radio. The usable range is limited to about 2 meters from the radio. The switch can also be mounted on a gun or the steering wheel of a car.


Wireless PTT button. The supplied rubber band can be used to mount the PTT button on a gun handguard or car steering wheel.


Mounting the PTT button on a rifle handguard. You can transmit while holding the rifle.
※ The rifle in the photo is not a British army item.

The wireless PTT button needs to be paired with the radio the same as a Bluetooth connection, however, connecting and disconnecting are differed from the Bluetooth specification. The button has its own methods, as explained below, which is also written in the operator’s guide.

Connecting:
1. Turn OFF the radio power and place the wireless PTT switch right next to the radio.
2. Turn ON the radio power An audio sound from the radio gradually becomes louder.
3. Push the wireless PTT button before the same sound restarts.
4. Release the PTT button.
5. If the sound volume gradually decreases, which indicates pairing has failed, restart the pairing from the beginning.

Disconnecting:
1. Turn OFF the radio power and place the wireless PTT switch right next to the radio.
2. Turn ON the power, and then push and release the wireless PTT button 5 times in 5 seconds.
3. If the electronic sound gradually disappears, the disconnect is successful.

The wireless PTT switch is attached with an adhesive, and it is impossible to open it to change the battery. It seems that once the battery runs out, buying a new switch is the only option. (Or I wonder if it could be possible to recharge through electromagnetic induction from the main device during the connection?)
Since the wireless PTT can only be operate within 2 meters from the radio, it may use low power radio waves. From what I have found on the internet, the unit seems to be using 433MHz in the ISM band, but I have not able to conduct a test to confirm it.

Operating Demonstration

I conducted a transmit test by attaching a dummy load to the PRR radio. With low output of 50mW, two PRR radios must be placed close to each other to communicate properly.

Optional supplied components

The part that connects the PTT switch and headset connector can be removed and replaced with several optional components that used for more functions. For example, a unit to connect a battle strategic communication system that is called “Bowman”, or connecting with a device that acts as a repeater in order to extent communication distance.


(Left) using flat-blade screwdriver to remove the cover because the slit of the screw is too thin for a British coin to insert and rotate to open.

Example of supplied components: Dual PTT switch
You can connect a unit with 2 PTT switches, so the PRR headset can be shared with external radios.


Optional components to connect headset with high power radios.

In addition to the PRR used for personal communication in the military, soldiers may also carry other radios for distant communications. The 2 optional components are used for connecting to the PTT switches, so both PRR and another radio can be used.


There are also optional units to connect with Harris, Motorola and ICOM radios. (Reference from the Leonardo S.p.A website)

Official model name
So called “PRR” is considered as a general name for the radio. This radio has an official model name of H-4855.

Summary

Even with the rather limited usage of the PRR transceiver radios, the optional components provide functions that extend the ability of operating through repeaters and connecting with other radios, which makes it a very interesting communication device.

What bothers me still is the lack of protection for water, drip or dust intrusion that is not mentioned on the product related website. Although I understand an average portable amateur radio with a MIL-SPEC is worth a point to emphasize, but at least the radio should be constructed with some sort of protection for the battery chamber from water and dust intrusion. An excuse that the battlefield in the Middle East does not rain much seems to be too far from the point. However, it makes sense if a low cost for each radio is required so that all soldiers can have one radio, so the cost must be the main consideration over durability or maintenance sustainability. Consequently, it could be that the military has a policy of “replace a new one if a malfunction occurs.”

Also, since it is not a radio with MIL-SPECs, there is not actually an official website of the radio for updated information. In addition to the British military, part of the American Navy has also been using this radio.

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