Configurations
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The RT-3600 / RT-3610 family consists of a relatively small number of parts, but there are an overwhelming number of possibilities to put these together into different installations. I'll try to document these on this page.
One thing that does complicate this job is the fact that during the more then twenty years the system was in use, new developments in the way of accessories were made, replacing older ones, while even up to the end of it's life cycle the RT-3600 configurations kept using parts that were originally developed for even older radios, like chest sets, handsets and antenna parts. So, it might just happen that the information presented here was at some stage during the development outdated by newer configurations. If you find such errors, please send me an e-mail.

Man Pack Configurations
Stacking them up...
Vehicular Configurations
Antenna Configurations
Audio Accessories


Man Pack Configurations

Both transceivers, the RT-3600 and the RT-3610, can be used carried on the back using either normal or rechargeable batteries. Manual 1/2 TH 11-170 (October 1 1969) gives the following configurations:

KL/PRC-3600 - NSN: 5820-17-054-6693

RT-3600 transceiver with
BX-3600 or BX-3601 Battery Box.
BG-3600 Carrying Harness
AT-272A/PRC Short Antenna
AT-271A/PRC Long Antenna  (+AB-129)
Handset - no further details given
Headset - no further details given
CX-3606 Cable Assembly - no further details given
KL/PRC-3610 - NSN: 5820-17-054-6695
RT-3610 transceiver with
BX-3610 or BX-3611 Battery Box
BG-3610 Carrying Harness
AT-272A/PRC Short Antenna
Handset - no further details given
Headset - no further details given
CX-3606 Cable Assembly - no further details given
Later documentation, FM-3600 / FM-4600 Nomenclatuur (August 1 1992) gives more details for hand- and headsets:
H-3600 Handset
H-3620 Headset
H-3625 Headphones
H-3630 Chest Set Group
It seems likely that the first portable sets used the old style handset H33/PT and old style headset consisting of the combination of chest set group AN/GSA-6 with headset microphone H-63/U. These were used extensively with the earlier generation of radios, the VRC/GRC/PRC series. The H-36xx accessories could well be a later development. As these older headsets and handsets used the old style 10 pin U-77 connector - and both the RT-3600 and the RT-3610 use a newer 5 pen audio connector - this would then explain what Cable Assembly CX-3606 would have to be: an interconnecting cable between the two audio connectors. In the newer manual this Cable Assembly is not longer mentioned as part of the man pack configurations.

Manual 1/2 TH 11-170 (Oktober 1 1969) mentions the BG-3600 Carrying Harness - in FM-3600 / FM-4600 Nomenclatuur (August 1 1992) this is replaced by the BG-4600, a harness for the newer and in 1992 coexisting RT-4600 radio. Drawings of the BG-3600 in early manuals indicate that this actually was a quite different harness then the later BG-4600, including extra bags for accessories.

The AT-272A/PRC short antenna mentioned for both man packs shows up as the AT--272/PRC in later manuals, whether this is an actual change in model is unknown. The AT-271A/PRC long antenna of course cannot be used without it's flexible base, the AB-129.

There are two variations of the battery box for each of the configurations. BX-3600 and BX-3610 are used with rechargeable batteries, the BX-3601 and BX-3611 are meant to be used with ordinary batteries.


Stacking them up...

All none portable configurations will use at least one extra box, apart from the actual transceiver. Here the somewhat strange concept of the RT-3600 comes into play, where the actual housing holds elements both at the front and at the back. Of course, the battery box at the end of the RT-3600 or RT-3610 will be replaced, but with the RT-3600 there is a choice between the simple JB-3600 Junction Box or the AM-3600 RF Amplifier, to create a thirty kilometre system.
The PP-3620 Power Supply has it's own very similar canister and comes on top of the RT-3600 - but here the front position can be chosen from either the AF-3620 Control- and Loudspeaker Unit or the IC-3620 Control- and Intercom Unit.
Two radios? Not a problem, a third canister with a second RT-3600 goes on top of the Power Supply. Again with the possibility to slip an amplifier in the back.

Three radios? Of course. But as there is a limit of three boxes in on stack, a second stack must be added next to the first one. Again, it must contain a Power Supply, with the same choice between a Control- and Intercom Unit or a Control- and Loudspeaker Unit in the front position. The third RT-3600 can be amplified if one so decides and goes underneath the Power Supply, so that the AF-3620 and/or IC-3620 units line up.

It's even possible to add a RT-3610 to one of the stacks, but the total number of radios is limited to three, as that is the maximum capacity of the switching elements.

Within a stack the interconnections are made on the back, with the UG-3626 Connector Assembly: two 26 pen connectors forming a short dog bone. The PP-3620 can accommodate two of these, so that's why it should be the middle element in a stack of three. Unusual in military radios, connections on the back - but it goes beyond that as the antenna connections on the AM-3600 or JB-3600 are also on the back of these units.

On the front of both the IC-3620 and AF-3620 there are two connectors for the intercom system, one on each side. As the intercom cabling is designed to daisy chain and go back to form a ring, even in a single stack system both will be used in order to close the ring. This makes the system much more secure, as a broken cable will not put the intercom boxes beyond the break out of commission. The system will still function without problems.
In a two stack set-up, this still holds true, as the two adjacent intercom connectors must be hooked up with the UG-3626 dog bone Connector Assembly. Again, the whole intercom cabling is a closed loop. So, the UG-3626 is used both to hook up the stacks vertically and horizontally.

Also on the front of the IC-3620 and the AF-3620 there are the connectors for the battery voltage. The IC-3620 has one, on the right hand side, the AF-3620 has two, one on each side, in order to daisy chain the power line. So, in a configuration with only one stack it does not really matter where the CX-3600 Power Cable goes, but with two stacks the AF-3620 must be on the right with the CX-3600 leading to the right hand connector. A UG-3608 dog bone Connector Assembly must be used to hook up the left hand power connector of the AF-3620 to the only power connector on the IC-3620, that is located on it's right side. And yes, having two IC-3620's in a two stack set is not possible, because the power connectors do not allow it. Apart from that, it would be useless as one IC-3620 will cater for the whole intercom system.


Vehicular Configurations

There are many, many possible vehicular configurations with these sets - and these configurations can be used in a lot of different vehicles. Or sometimes even in other situations, as some configurations were for instance especially put together for the classroom.
In order to limit the logistics problems the problem was split in two: radios sets, that come under a numbering system that starts with KL/VRC and all the extra's to fit these in different vehicles, MX sets. So, for each possible use of the radios there will be a combination of a KL/VRC set and an MX set. As if this is not complicated enough, all these combinations have their own FM-codes where the vehicle types are also coded numerically. At a later time I might add that information to this web site...

The simplest radio configurations given in FM-3600 / FM-4600 Nomenclatuur (August 1 1992) are:

KL/VRC-3620 - NSN: 5820-17-054-6711

RT-3600 transceiver with
AF-3620 Control- and Loudspeaker Unit
JB-3600 Junction Box
MT-3620 Mounting
PP-3620 Power Supply
RF-3620 Antenna Tuner / Mounting
UG-3626 Connector 26 pen
KL/VRC-3610 - NSN: 5820-17-055-0932
RT-3610 transceiver with
AF-3620 Control- and Loudspeaker Unit
JB-3610 Junction Box
MT-3620 Mounting
PP-3620 Power Supply
RF-3610 Antenna Tuner / Mounting (reducing)
UG-3626 Connector 26 pen
These are full radio systems, but they lack all extra material as audio accessories, cabling etceteras. In fact, there are seven different MX sets that can be combined with the KL/VRC-3620 to make different installations. For instance, to make a FM-36/1120 for the Nekaf Jeep:

MX-4253 - NSN: 5820-17-036-0694

Antenna Tip
Antenna Tie Down Rope
AS-1730VRCMD Antenna Element
AT-1095/VRC Antenna Element
AB-377 Antenna Segments Stowage Bag
Antenna Mounting (For RF-3620 Antenna Tuner / Mounting)
Mounting (Antenna?) Tuning Unit
BG-3601 Carrying Bag Extra Parts
H-3600 Handset
H-3620 Headset
H-3630 Chest Set Group
M-3600 Microphone
CX-3600 Power Cable
JB-3620 Junction Box
MT-3622 Mounting (For JB-3620 Junction Box)
MT-4196 Mounting Electrical Material (Base for the MT-3620 that in it's turn is the base for the RT-3600)
CG-3602 Antenna Cable
This is a relatively simple set - just the one standard power radio and no intercom facilities. All audio accessories are the new style five pen connector.
A double radio with intercom would be:

KL/VRC-3622 - NSN: 5820-17-054-6712

RT-3600 (2x) transceivers with
IC-3620 (1x) Control- and Intercom unit
JB-3600 (2x) Junction Box
MT-3620 (1x) Mounting
PP-3620 (1x) Power Supply
RF-3620 (2x) Antenna Tuner / Mounting
UG-3626 (1x) Connector 26 pen
The numbers between brackets indicate the number of each item needed. Now, if this set would be used in the Leopard I tank, a MX-4296 comes into play. This is just one of the seven MX sets that could be used with the KL/VRC-3622.

MX-4296 - NSN: 5820-17-036-0736

Antenna Tip (2x)
Antenna Tie Down Rope (3x)
AS-1730VRCMD (2x) Antenna Element
AT-1095/VRC (2x) Antenna Element
AB-377 Antenna Segments Stowage Bag (2x)
BG-3601 (1x) Carrying Bag Extra Parts
H---33E/PT (1x) Handset
H-5696 (6x) Tank Helmet
JB-3620 (2x) Junction Box
MT-3622 (2x) Mounting (For JB-3620 Junction Box)
C-3621 (4x) Intercom Box
MT-3621 (4x) Mounting (For Intercom Box)
CG-3601 (1x) Antenna Cable
CG-3602 (1x) Antenna Cable
CX-3600 (1x) Power Cable
CX-3611 (3x) Intercom Cable
CX-3612 (1x) Intercom Cable
CX-3613 (1x) Intercom Cable
CX-3614 (2x) Intercom Cable
Lots of cabling this time, as is to be expected when many crew members must be able to communicate through the intercom system. No loudspeakers - as they would not be heard in the noisy interior of that Leopard I. Less special extra mounting hardware, as there will be a standard radio table in the turret - the jeep had none, so it needed an extra mounting. And a older type handset - but because all audio connectors on the Intercom Boxes are the old 10 pen standard, that does not matter.

Antenna Configurations

As both the RT-3600 and the RT-3610 can be used as man pack or as vehicular systems, they use a lot of different antenna configurations. The small RT-3610 in portable use is the simplest: it can only work with the AT-272A/PRC. A man pack RT-3600 also uses the AT-272A/PRC as it's short antenna option, but as the long antenna it uses the AT-271A/PRC. All these antenna's must be hooked up to the front of the sets.

A RT-3610 in a vehicular set-up will firstly need to loose it's BX-3610 or BX-3611 Battery Box. It must be replaced by a JB-3610 Junction Box that connects the system to the stack it is part of, through backside connector 752. It also provides on the backside connector 751 for the antenna cable CG-362x, a simple coaxial cable. On the other end of this cable there must be a RF-3610 Antenna Tuner, that doubles as the antenna base and accommodates antenna sections MS-117A and MS-118A/K. That RF-3610 actually is not a real Antenna Tuner, it only has a coaxial connector for the H.F. signals as well as some internal circuitry in order to weaken the signal strength when desired - read on for further information...

The vehicular RT-3600 also looses the BX-3600 or BX-3610 Battery Box, to be replaced with either the JB-3600 Junction Box or the AM-3600 RF amplifier. Both options provide three connectors on the back. On the JB-3600 701 hooks up to the stack again, as does 601 on the AM-3600. Connector 703 (603 on the AM-3600) is the coaxial antenna connection and 702 (602) provides the control signal for the antenna tuner - needed to actually tune the antenna to the chosen frequency.
Normally Junction Box JB-3620 comes next in the chain. It comes with it's own mounting, the MT-3622 and on the bottom has two permanently attached short cables that connect to 602/702 for the control signals and 603/703 for the hf signals. On the top there is connector 901, where control- and hf signals combine. This connector takes a one meter cable CG-3601 or longer (up to ten meters: CG-3610) that goes to the RF-3620 antenna tuner/base. This automatic tuner will automatically tune the combined antenna elements AS-1730VRCMD and AT-1095/VRC to the used frequency. And if you'd need more length in antenna cable: there are extension cables CG-3611 up to at least CG-3615, with the last digit indicating the length in meters.
If all this seems slightly complicated and overdone, using a JB-3620 Junction Box with it's own MT-3622 mounting, just to combine the signals for the antenna cable - it is. In the later RT-4600 radio this circus was simplified to a single cable, the CG-5826, with the two leads to the RT on one end and a connector for the antenna tuner/base on the other end. And though it is not documented, this cable fits the RT-3600 set-up just as well, cutting out the separate junction box, it's mounting and the antenna cable.

Then the plot thickens. Because the RT-3600 can play three roles: it's an eight kilometre transceiver by it's sweet self, a thirty kilometre apparatus with the added AM-3600 RF amplifier but it can also be put to use as a short range - three kilometre, same as the RT-3610 - system. Of course, when used as a short range three kilometre transceiver the RT-3600 will be fitted with the JB-3600, not with the amplifier. But even then the signal strength is too strong, so the RF-3610 comes into play, as it can be used as a limiter. It's hooked up to the 703 connector of the JB-3600 by means of a cable CG-362x. No further cabling is needed, as this RF-3610 does not need information for tuning and connector 602 or 702 stays unused.. However, if used this way the RF-3610 needs a simple manual internal modification - and whether the RF-3610 is set up for use as a limiter/tuner for the RT-3600 or as a tuner only for the RT-3600 should be indicated by a reversible indication on the outside.

The story so far is what is indicated in the early manuals on these sets. However, in later documentation, all of a sudden the AB-15/GR Antenna Base shows up. This is a much simpler beast then the RF-3610 - it has no built in limiter, it is literally just an antenna base. So, the only radio it could serve is the RT-3610. It would seem likely that at some stage during the life cycle of this radio family someone decided it would be cheaper to use or re-use this older material.
Another development along the same lines would be the appearance of the BX-3610A as a replacement for the JB-3610. Basically this BX-3610A is a rebuilt Battery Box, that no longer can hold batteries but is fitted with a fixed cable that ties in the RT-3610 into the stack it is fitted on. What baffles me however is the fact that this BX-3610A has no HF connector, where the JB-3610 has one. So, how did they hook up the antenna to a RT-3610 equipped with the BX-3610A? Only solution I see is through the original Antenna Connector on the front of the set. And that is specifically made to accept the AT-272A/PRC portable antenna. So a RT-3610 hooked up in this configuration could only be used in an open vehicle.

If the need arises, there is also an Antenna Mast: AB-3600.


Audio Accessories

As to the audio accessories, handsets, microphones, headphones and such, it is rather hard to get a clear picture of what was actually used with the RT-3600 / RT-3610 family. It would seem that during it's lifetime some changes were made in these.

The first problem is of course that the audio connectors in the system are of two very different types. Both transceivers each have two of the new style 5 pen connectors, all other audio connectors throughout the system are old style 10 pen - the U-77/U. To complicate matters there is a adaptor between the two standards, that I never have seen mentioned in the manuals. My conclusion to date is that all vehicular installations used old style connector audio accessories exclusively.

Then, there are a number of basically different approaches to audio accessories when it comes to military radios. To sum up the approaches I have found within the RT-3600/RT-3610 family:

Handsets - the simple handset, quite like found on a ordinary telephone, but with a pressel switch for transmitting and a much slimmer earpiece, as it would have to fit under a helmet. The RT-3600/RT-3610 family uses a lot of these:

  • H-33/F/GY (10 pen) - an older handset, apparently being re-used here.
  • H-33E/PT (10 pen) - an older handset, apparently being re-used here.
  • H-3600 (5 pen)  - used exclusively in man pack configurations.
  • H-3610 (10 pen) - usage vehicular - further details unknown.
  • H-6060 (5 pen) - used exclusively with the KL/GRA-3686 Remote Control Set.
  • H-7188 (no connector, but two clips) - usage unknown. Has no pressel switch. Some documentation seems to indicate this was used as the external Field Telephone (Bos Veld Telefoon), to be connected to the back of the PP-3620 Junction Box.

Headsets - basically a headphone with a boom microphone. Obviously not to ideal when wearing a helmet - and how does one switch on the transmitters? With a chest set!

  • H-3620  (special connector) - used exclusively in man pack configurations, with the H-3630 Chest Set. Leaving the operator without his helmet.

Chest Sets - the solution to switching on transmitters with a headset: the switches are in a small control box strapped to the chest of the person using the headset. Later solutions are not strapped any more, but clipped on to the front of the overall. In both cases there will be a quick release in the cabling, see under tank helmets. I know of two systems used:

  • AN/GSA-6 (10 pen) - only for vehicular use, to be used with the T-30-V Throat Microphone and the H-4016 Headphone. An old Chest Set this, it was used with earlier families of radios extensively - but with other audio gear.
  • H-3630 (5 pen) - used exclusively in man pack configurations, with the H-3620 Headset.

Microphones (Hand) - when stationary, a combination of a loudspeaker and a hand microphone is ideal. The microphone will have the pressel switch to open up the transmitter. When more operators are sharing the same room, or noise levels are high, the loudspeaker can be replaced by a simple headset.

Microphones (Throat) - different approach to the microphone. Very good in high noise environments like armoured vehicles and it leaves both hands free - until you need to find that pressel switch. That is why throat microphones are always part of a chest set configuration.

  • T-30-V (special connector) - used exclusively with the AN/GSA-6 Chest Set.

Headphones

  • H-3625 (5 pen) - used exclusively in man pack configurations.
  • H-4016 (special connector) - used exclusively with the AN/GSA-6 Chest Set.

Tank Helmets - are actually a re-invented chest sets. Earpieces and boom microphone are included in a tight fitting fabric helmet with added protection against bumping heads in vehicles on the move in rough terrain. The switches - on the examples I know - are on one of the earpieces, so transmitting means pressing that switch.
Another thing with tank helmets (and chest sets): there might be a time when you want to get out of that tank very, very quickly. Like when for instance it is on fire. Happens during battle, it seems. But escaping death from burning only to snap your neck when jumping out the turret, because you did not take the time to remove that tank helmet, seems stupid. So, a tank helmet - and all other headset like audio accessories in those environments - will incorporate a quick release in it's cabling, that just snaps open when there is enough force on it.

Loudspeakers - great for stationary work - also often found in jeeps for general listening for signals. The RT-3600/RT-3610 family uses two:

  • LS-166/U (10 pen) - an older era loudspeaker with the U-77/U connector, used exclusively with the KL/GRA-3686 Remote Control Set.
  • LS-3621 (10 pen) - an amplified loudspeaker, still using the old U-77/U connector, is the basic speaker for the family.

Last updated: 12-11-2003 23:21 +0100
Copyright 2001, 2002, 2003, 2004, 2005 A.J.M.O. Witkop. All Rights Reserved.