Click for homepage
RT-4600 →
Philips RT-3600
Wide-band analog VHF military radio

RT-3600 was an VHF wide-band FM military radio set, developed for the Dutch Army by Philips Telecommunications Industry (PTI) in Hilversum (Netherlands) during the late 1960s and early 1970s. The RT-3600 was an extremely robust radio and, although it was phased-out in the late 1990s, many of them were still in use in 2011. They are also popular with collectors and hams. The radio covers 26-70 MHz with 10 kHz deviation and a channel spacing of 50 kHz. Output power is 2W, but can be inreased to 30W by installing the (optional) AM-3600 power amplifier.

The RT-3600 radio is often used in combination with other units, such as the IC-3620 intercom and the AF-6320 speaker unit. Furthermore, a wide variety of accessories are available for it, such as junction boxes, microphones, speakers, handsets, headsets and voice encryption units.

The image on the right shows a typical setup, consisting of the RT-3600 radio itself (bottom) and the IC-3620 intercom (top). The intercom was suitable for three radios. The second radio would be placed on top of the stack and the third one (if present) was placed aside the stack.

The contacts between PTI and the Dutch Department of Defense (DoD) date back to the early 1960s. In the late 1960s, PTI was asked to develop a tactical VHF radio for the Army, based on a design by the Army's own R&D department Laboratorium Elektronische Ontwikkeling Krijgsmacht (LEOK) [1]. After a series of failures, this resulted in the extremely robust RT-3600 that can be dropped at any angle, from a height of 1.20 meter. It is rumoured that an RT-3600 — dropped by accident from a helicopter in Argentina — was still operational after it had been recovered [1].

In the early 1980s, following a series of reorganizations at Philips, PTI became part of Holland Signaal (HSA) 1 and was renamed Signaal Communications. In 1984, Signaal was commissioned by the DoD to develop the RT-4600 as the successor to the RT-3600. In 1989, just before the company was taken over by Thomson (now: Thales), they developed the SPIDER manpack radio.

  1. After the reorganisation, the company name was officially Hollandse Signaal Apparaten (HSA), but was commonly abbreviated to Holland Signaal or Signaal Huizen.

RT-3600 radio
Front view of the RT-3600
Rear view of the RT-3600
Front view of the IC-6320 intercom
Rear view of the IC-6320 intercom
RT-3600 radio (bottom) and IC-6320 intercom (top)
RT-3600 radio (bottom) and IC-6320 intercom (top)
RT-3600 radio (bottom) and IC-6320 intercom (top)
1 / 8
RT-3600 radio
2 / 8
Front view of the RT-3600
3 / 8
Rear view of the RT-3600
4 / 8
Front view of the IC-6320 intercom
5 / 8
Rear view of the IC-6320 intercom
6 / 8
RT-3600 radio (bottom) and IC-6320 intercom (top)
7 / 8
RT-3600 radio (bottom) and IC-6320 intercom (top)
8 / 8
RT-3600 radio (bottom) and IC-6320 intercom (top)

Voice encryption
During the Cold War, the Eastern Bloc countries constantly monitored the radio frequencies of the Allied FOrces in West-Germany. Nevertheless, speech encryption was hardly ever used at a tactical level. During most, if not all, large NATO exercises in Germany in the 1970s and 1980s, all tactical radio traffic went through the air in clear (i.e. unencrypted). Luckily, the RT-3600 was designed with encryption in mind, and at a higher level the following encryptors were used:

It is little known that in the late 1960s, another Philips subsidary, Philips Usfa NV in Eindhoven (Netherlands), started development of a tactical speech encryption system for the RT-3600. It was called Spendex-10 and was released in 1973, after an intensive period of experiments.

The image on the right shows the final version of the Spendex-10, seated on top of the IC-3620 intercom. The RT-3600 radio is at the bottom. The device is connected between the handset and the RT-3600 radio, by means of a 5-pin cable at the right. It is powered by the IC-3620.

Spendex 10 provided extremely good security, even by todays standards, and matched the design of the RT-3600 radio set. It could even transmit and receive digital data (at 600 baud) and could also be connected directly to the FM-200 line-of-sight radio link (LOS). Despite the good results, only a small quantity was ever built and the device was not taken into large scale production.

When using voice encryption with the RT-3600, the Mode Selector (squelch) should be set to the rightmost position marked 'X' [A]. In the X-mode any filtering in the transmission and reception path is bypassed, in order to support wideband data signals. Furthermore, the squelch is always open and noise cancelling is handled by the encryption device. The Spendex-10 has a built-in automatic analog and digital squelch.

Apart from the Spendex 10, the RT-3600 was also used in combination with the much smaller American KY-57 voice and data encryption unit.

Developed in the mid-1970s and used by the American armed forces and NATO, KY-57 featured the secret SAVILLE encryption algorithm developed by the NSA and GCHQ. KY-57 was succeeded in 1993 by the backwards compatible KY-99, which could also be used with the Philips RT-3600.

Voice encryptors used with RT-3600
Philips Spendex-10, Narrow-band Voice and Data Terminal
Wide-band Voice and Data Encryption Unit
Narrow-band Voice and Data Terminal
Power Amplifier   AM-3600
The RF output power of the RT-3600 is between 1 and 2 W, which should be sufficient for an operational rangen of approx. 3 km. The range can be extended by installing the (optional) AM-3600 into the rear end of the radio. Once installed, the AM-3600 offers the following settings:

  • Low
    8 km
    0.95 - 1.75 W
  • Medium
    15 km
    8 - 15 W
  • High
    30 km
    25 - 45 W
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


Audio socket   U-79/U
There are several ways to connect a microphone or a handset to the RT-3600. In the Dutch Army, the most common way was to connect a handset with a 10-pin U-77/U plug to the IC-3620 intercom unit, or to any of the junction boxes in a vehicle (which were connected to the IC-3620).

  1. SPK
    Speaker output (regulated)
  2. SPK GND
    Speaker return
  3. MIC RAD
    Microphone to radio
  4. AF LINE
    Audio line out (fixed)
  5. MIC GND
    Microphone return
  6. PTT
  7. PTT GND
    Push-to-Talk return
  8. n.c.
  9. MIC IC
    Microphone to intercom
  10. SPK +18V
    +18V power for speaker
Audio socket   U-229
It is also possible to connect a handset directly to the RT-3600 radio. At the front right of the radio are two standard 5-pin U-229 connectors. When using these connectors, please note that the wiring of these connectors is different the common NATO/USA standard. For the RT-3600 the lines for microphone (MIC) and speaker (SPK) are swapped, as shown in the table below [3].

  1. GND
  2. MIC
    Microphone 1
  3. PTT
  4. SPK
    Speaker 1
  5. n.c.
  1. Compared to the US/NATO standard, these lines are swapped.

When using the 5-pin audio connector on the RT-3600, this means that you must either use the standard microphone/handset that was issued with this radio, or modify a standard NATO or USA handset according to the specification above. At some point, a NATO convertor box was issued, allowing NATO handsets to be used with the RT-3600, but all it does is swap lines B and D.

 More about the use of the U-229 connector

  • Device
    VHF/FM transceiver
  • Purpose
    Military communications
  • Year
  • Model
  • Manufactuer
  • Country
  • Successor
  • Frequency
    26.000 - 69.950 MHz
  • Bands
    2: 26-47 MHz,47-70 MHz
  • Encryption
  • Modulation
  • Channels
  • Spacing
    50 kHz
  • Deviation
    10 kHz
  • RF power
    1W/2W (or 8W/30W with AM-3600 amplifier)
  • Range
    8 km (or 30 km with AM-3600 amplifier)
  • Squelch
    CTCSS (150 Hz)
  • Power
    24V DC (or 15V during portable use)
Designator NSN Description
RT-3600 5820-17-708-9880 Transceiver
AF-3620 5820-17-708-9895 Amplifier/Loudspeaker unit
AM-3600 5820-17-708-9885 30W HF amplifier (PA) — internal
IC-3620 5820-17-708-9891 Intercom unit
RF-3620 5985-17-035-4488 Antenna tuning unit (part of antenna assembly)
PP-3620 5820-17-708-9892 Power supply unit
BX-3600 ? Battery box (for portable use)
BX-3601 ? Battery box (for portable use)
H-3600 5965-17-035-8553 Handset with 5-pin U-229 connector 1
H-3610 5965-17-037-5776 Handset 10-pin U-79/U connector
M-3600 5965-17-037-5804 Microphone with 5-pin U-229 connector 1
M-3610 5965-17-037-5805 Microphone with 10-pin U-79/U connector
H-3620 5965-17-037-5777 Headset with microphone (for chest set)
H-3630 5965-17-037-5778 Chest set with 5-pin U-229 connector 1
GSA-6A 5965-00-329-9085 Chest set with 10-pin U-79/U connector
H-4016 5965-17-032-7046 Headset for chest set
T-30 5965-17-032-8786 Throat microphone for chest set
LS-3621 5965-17-708-9898 Loudspeaker with 10-pin U-79/U connector
C-3621 5930-17-708-9887 Switch box for intercom
GRA-6 ? Remote control set
GRA-3686 ? Remote control set
UG-3608 5935-17-034-8426 8-pin connector assembly
UG-3626 5935-17-034-8427 26-pin connector assembly (bridge)
CX-3600 5995-17-034-3959 Power cable 24V
CX-3611 5995-17-034-3963 Intercom cable (1 m) IC-3620 to C-3621
MT-3620 5820-17-708-9896 Mounting base for RT-3600
MT-3621 5975-17-033-3037 Mounting base for intercom switch box
MT-3622 5975-17-033-8240 Mounting base for JB-3620
MT-5120 5975-17-049-7740 Mounting for fitting RT-3610 to RT-3600
MT-4196 5985-17-035-4503 Mounting rack for Nekaf
BG-3600 ? Carrying harness for RT-3600
BG-3601 5820-17-039-3319 Carrying bag for RT-3600 accessories
BG-3610 5820-17-039-3319 Carrying harness for RT-3610
AT-272A ? Short antenna (for portable use)
AT-271A ? Long antenna (for portable use)
CX-3603 ? Cable set (for portable use)
JB-3620 5820-17-032-9109 Junction box for antenna cable
Top 5820-00-437-2353 Antenna tip
Tuitouw 5820-00-908-6416 Antenna tie-down (rope)
AT-1095 5820-00-856-2728 Upper antenna segment
AT-1730 5985-17-055-3230 Lower antenna segment
AB-377 5985-17-039-9943 Antenna storage case (canvas)
AB-5242 5985-17-039-9646 Antenna tuning unit
? 5985-17-039-6927 Antenna base
CG-3601 5995-17-034-3956 Antenna cable (1 m) JB-3620 to RF-3620
CG-3602 5995-17-034-3957 Antenna cable (2 m) JB-3620 to RF-3620
CG-3603 5995-17-034-3958 Antenna cable (3 m) JB-3620 to RF-3620
CG-3604 5995-17-034-3960 Antenna cable (4 m) JB-3620 to RF-3620
CG-3605 5995-17-034-3961 Antenna cable (5 m) JB-3620 to RF-3620
CG-3606 5995-17-048-3247 Antenna cable (6 m) JB-3620 to RF-3620
CG-3610 5995-17-039-0225 Antenna cable (10 m) JB-3620 to RF-3620
GC-3613 5995-17-039-0223 Antenna extension cable (3 m)
GC-3615 5995-17-039-0224 Antenna extension cable (5 m)
  1. Non-standard wiring.  More

  1. Technische Handleiding, RT-3600
    Bediening en 1e echelons onderhoud (Dutch).
    Konklijke Landmacht, 28 October 1974.
  1. Raoul de Zoeten, Historie van de RT-3600 (Dutch)
    Website. RT-3600 history.

  2. Wammes Witkop, RT-3600 Parts
    Website 'Green Radios'. Overview of all RT-3600 parts and accessories.

  3. Richard Lacroix, Audio Connectors U-229/U
    Website. MilSpec Communication Canada.
Further information
Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Created: Saturday 16 July 2011. Last changed: Sunday, 26 May 2024 - 16:51 CET.
Click for homepage