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Philips RT-4600
Wide-band analog VHF military radio

RT-4600 was a modular VHF-L FM military radio set developed by Philips Telecommunications Industry (PTI) in Hilversum (Netherlands) as the successor to the successful RT-3600. The radio set was built especially for use by the Dutch Army and was first introduced in 1984. It was also successfully exported to other countries. The RT-4600 was succeeded in 2000 by the FM-9000.

Externally, the RT-4600 strongly resembles its predecessor, the RT-3600. It is housed in the same robust enclosure and fits the same vehicle mount. Most of the accessories are similar to those of the RT-3600. The frequency range has changed slightly and now covers 30 to 75.975 MHz in 25 kHz 1 steps rather than 50 kHz steps.

Internally, the radio is completely different how­ever. It has clearly been designed to save on cost and is far less robust than its predecessor. The internal wiring has been replaced by a large PCB that acts as a backplane, which makes the radio far more vulnerable to vibrations and shocks.

Much of the filtering, that gave the RT-3600 its excellent selectivity and large signal behaviour, has been left out, and is now located inside the additional FB-4620 filter unit. The image on the right shows a complete radio station, consisting of an RT-4600 transceiver, AF-4620 audio unit, FB-4620 filter unit and standard vehicle mount.
RT-4600 radio set, consisting of transceiver, intercom and filter unit

The RT-4600 was developed by Philips PTI (later renamed to Signaal) in the early 1980s as the successor to the RT-3600 that had become too expensive to manufacture, mainly because of its extremely robust mechanical structure. Much of the mechanics were replaced by electronics, which made the RT-4600 far more sensitive to vibrations, especially when mounted in a tank.

It never gained much popularity in the Dutch Army, not least because the RT-3600 wasn't phased out when the RT-4600 was introduced. That said, it was successfully sold to other countries. The RT-3600 and the RT-4600 remained in use until 2000 when they were replaced by the FM-9000.

  1. Versions with a black front panel have a 50 kHz channel spacing.

RT-4600 radio set, consisting of transceiver, intercom and filter unit
Front view
RT-4600 transceiver
AF-4620 audio unit
FB-4620 Filter Box
Connections at the rear
Antenna base
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RT-4600 radio set, consisting of transceiver, intercom and filter unit
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Front view
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RT-4600 transceiver
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AF-4620 audio unit
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FB-4620 Filter Box
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Connections at the rear
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Antenna base
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Voice and data encryption
The RT-4600 was suitable for the connection of an external encryption/decryption device that could be inserted between the handset and the U-229 audio socket of the transceiver. Like on the RT-3600, the MODE-selector has a so-called X-position, which bypasses the audio filtering.

When set to the X-position, both the transmitter and the receiver are suitable for digital audio signals, allowing a wide variety of digital voice and data encryption devices to be used, such as the American KY-57, the more versatile KY-99 or the little known Philips Spendex 10. The image on the right shows a typical KY-57 unit.

When used with a digital encryption device, other users of the radio channel (without access to encryption) will only hear white noise, as if the squelch has been released. Only users with the same encryption key can hear each other.
KY-57 voice encryption unit

Philips even developed a small high-end encryption device especially for the RT-4600, but it was never taken into production. The device was known as ORTHROS and was fully integrated with the handset. Although Philips even won an award for its design, it was not taken into production, probably because better priced alternatives had meanwhile become available from other sources. Examples are the American KY-189 and the KY-57 shown above, that was also used with NATO.

Encryption devices used with the RT-4600
Spendex-10 tactical speech encryptor with Delta Modulation
KY-57 (VINSON) Wide-band Voice and Data Encryption Unit
Narrow-band Voice and Data Terminal
Mobile secure radio voice system
Voice scrambler handset
The RT-4600 is a modular system that allows the radio set to be adapted for many applications. The standard radio set is suitable for mounting inside a vehicle, but can easily be converted into a manpack radio by replacing the PP-4621 power supply unit at the rear end by a battery pack.

Two variants of the RT-4600 are known: one with a 25 kHz channel spacing and one with 50 kHz channel spacing. The 50 kHz variant can be recognised by a black front panel. The one featured on this page is the 25 kHz variant.

  • 25 kHz
    Green front panel
  • 50 kHz
    Black front panel
Remote control set   KL/GRA-3686
Up to two RT-3600 radios can be controlled remotely via a 2-wire field line of up to 3 km long, by means of the KL/GRA-3686 Remote Control Set shown in the image on the right.

The set consists of two boxes that should be installed at both ends of the 2-wire field line. The leftmost is connected to the radio(s). A H-5050 handset can be connected to either box, allowing the radios to be used in simplex as well as half-duplex (split frequency) mode.

 More information


  • Frequency
    30.000 - 75.975 MHz
  • Modulation
  • Channels
  • Spacing
    25 kHz or 50 kHz 1
  • RF power
    2, 10 or 30 Watt
  • Sensitivity
    0.2µV / 20dB
  • Power
    12V (RT-4600) or 24V (VRC-4622)
  1. Only on units with a black front panel.

  • RT-4600
    Transceiver (Transmitter/Receiver), powered by 12V
  • AF-4620
    Amplifier/Loudspeaker unit, powered by 24V
  • FB-4620
    Filter Box
  • AM-4600
    Power Amplifier for 30 Watt output (30 km)
  • PP-4621
    Internal PSU
  • VRC-4622
    Radioset, consisting of RT-4600 and AF-4620
  • KL/GRA-3686
    Remote control set
  1. Raoul de Zoeten, Historie van de RT-3600 (Dutch)
    Website. RT-3600 history.
Further information
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Crypto Museum. Created: Friday 22 July 2016. Last changed: Sunday, 22 November 2020 - 17:30 CET.
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