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Philips RT-4600 →
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.
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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.
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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.
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After the reorganisation, the company name was officially
Hollandse Signaal Apparaten (HSA),
but was commonly abbreviated to Holland Signaal or
Signaal Huizen.
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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:
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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.
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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.
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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.
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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.
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Voice encryptors used with RT-3600
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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:
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Low 8 km 0.95 - 1.75 W Medium 15 km 8 - 15 W High 30 km 25 - 45 W
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Remote control set
KL/GRA-3686
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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
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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).
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SPK Speaker output (regulated) SPK GND Speaker return MIC RAD Microphone to radio AF LINE Audio line out (fixed) MIC GND Microphone return PTT Push-to-Talk PTT GND Push-to-Talk return n.c. unused MIC IC Microphone to intercom SPK +18V +18V power for speaker
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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].
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GND Ground MIC Microphone 1 PTT Push-To-Talk SPK Speaker 1 n.c. Unused
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Compared to the US/NATO standard, these lines are swapped.
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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
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Device VHF/FM transceiver Purpose Military communications Year 1972 Model RT-3600 Manufactuer PTI Country Netherlands Successor RT-4600 Frequency 26.000 - 69.950 MHz Bands 2: 26-47 MHz,47-70 MHz Encryption External Modulation FM Channels 880 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)
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Non-standard wiring.
➤ More
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- Technische Handleiding, RT-3600
Bediening en 1e echelons onderhoud (Dutch).
Konklijke Landmacht, 28 October 1974.
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© Crypto Museum. Created: Saturday 16 July 2011. Last changed: Thursday, 10 October 2024 - 14:12 CET.
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