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Wide-band analog VHF military radio
RT-3600 was an VHF wide-band analog military radio, 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 are still used today.
They are also popular with collectors and radio hams.
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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, etc.
The image on the right shows a typical setup, consisting of an RT-3600
radio (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) next to it.
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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, they were asked to
develop a robust HF radio for the Army, based on a design by the Army's
own R&D department Laboratorium Elektronische Ontwikkeling
Krijsmacht (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, that was dropped by accident
out off a helicopter in Argentina, was still working after it was
recovered.
In the early 1980s, following a series of reorganizations at Philips,
PTI became part of Holland Signaal (HSA) and was renamed Signaal
Communications. They were commissioned by the DoD to
develop the successor: the RT-4600.
In 1989, HSA was sold to Thomson (now: Thales).
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Although it was known that, during the Cold War, the enemy was monitoring
our frequencies, speech encryption was hardly ever used at a tactical level.
During most, if not all, large-scale NATO excercises in Germany, all
tactical conversations went through the air en clair.
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It is little known that in the late 1960s, another Philips subsidary,
Philips Usfa in Eindhoven (Netherlands),
started development of a tactical speech encryption system for the RT-3600.
It was called Spendex-10 and
in 1973, after a long range of experiments, the device was ready.
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 in between the handset and the RT-3600, by means
of a 5-pin cable at the right. It is powered by the IC-3620.
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It 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.
More...
When using a voice encryption with the RT-3600, the Mode Selector
(squelch) should be set to the rightmost position marked 'X' [3]. In this mode,
the radio can use a larger bandwidth than when using normal speech.
Any filtering in the transmission and reception path are bypassed this way.
In this position, the squelch will always be open and any noise supression
will have to be done by the encryption-device.
The Spendex-10
has an automatic analog and digital squelch.
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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
connector to either the IC-3620 intercom unit, or to any of the junction
boxes in a vehicle.
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) need to
be swapped. The table below shows both the RT-3600 wiring and
the more common NATO wiring [4].
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| Pin
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RT-3600
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NATO
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Description
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| A
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GND
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GND
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Ground (common wire)
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| B
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MIC
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SPK
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Microphone (RT-3600) or speaker
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| C
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PTT
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PTT
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Push-to-Talk switch (connects to ground)
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| D
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SPK
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MIC
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Speaker (RT-3600) or microphone
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| E
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n.c.
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n.c.
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Generally not used
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When using the 5-pin audio connector on the RT-3600, this means that you
either need to use the standard microphone/handset that was issued with this
radio, or modify a standard NATO or USA handset according to the table above.
At some point, a NATO convertor box was issued, to allow NATO handsets to
be used with the RT-3600, but all it does is swap lines B and D.
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Thursday, 13 December 2012 - 22:44 CET
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