Past, Present and Future of Tactical Radios – Part 8

Before the Christmas break, I left off the discussion of tactical radios discussing different issues and requirements from the late 1970s and early 1980s.  The main reason I didn’t jump from the Vietnam era radios straight into the first digital radios was to give those issues and requirements their proper air, as they lead directly to the advantages and limitations of that radio system.

The Army started development of the replacement for VRC-12 and PRC-77 radios, now called Combat Net Radios (CNR), in 1974.   The technical requirements, as mentioned in the previous post, included enhanced communications security, support for digital traffic, and improved reliability.  The Army needed highly reliable communications to synchronize lean force structure in combined arms operations.   After a decade and a half of work, around 1988, the Army fielded the SINgle Channel Ground and Airborne Radio System, or SINCGARS for short, to front line units.

U.S. Army photo.
AN/PRC-119 Backpack SINCGARS

SINCGARS consisted of a modular set of radios equipping ground units, paired with compatible aircraft radios.  These were not just “Army” sets, but also used by the Marines, Air Force, and Navy.  The aircraft sets are outside the scope of this study, but the chart below breaks down the major components of the SINCGARS ground variants.

The radio itself evolved through several generations, but the supporting components remained the same generally speaking.  The AS-3900 antenna sensed the radio transmit frequency and automatically adjusted resistance to match, eliminating the “clacking” matching units of the old VRC-12 series.  For command posts, the OE-254 antenna (three up and three down) did not require reconfiguration with frequency changes, as with the older RC-292.  The power amplifier boosted transmit power to allow a planning range of 40 km.  (Many units would report 50 km out in the desert.)  Without the amplifier, SINCGARS ranged about 10 km.

OE-254 Antenna

SINCGARS transmitted on the frequency range of 30 to 88 Mhz.  By reducing the channel separation to 25 Khz, SINCGARS doubled the number of available channels.   Radio operators keyed in the frequency from a numeric pad on the front of the radio.  Gone was the old dial; replaced by an LED digital display.  SINCGARS had space for six pre-set frequencies (and two additional spaces reserved for special functions described below).  The radio operated in single channel (SC) mode or frequency hop (FH) mode.

The backpack versions (PRC-119 or dismounted VRCs) weighed about 20 pounds when dressed out (comparable to a PRC-77 with KY-57).  The BA-5590 (same used on the KY-57 VINSON), gave about six to eight hours of life (if you were lucky).  Field experience lead me to plan for a 6 km range, instead of the 10 km range noted in the technical manuals.

At the heart of SINCGARS was a frequency hopping technology which addressed the long-standing jamming and intercept threat.  Simply put, in frequency hop mode the radio skip 100 times a second through the frequency range.  To work properly, the radio needed five keys, or variables.  First a crypto key for encryption.  Second a TranSec (TSK) that provided the hopping pattern.  Third a HopSet specifying the set of frequencies to use.  Fourth the NetID, a number between 000 and 999, identified the radio network.  And lastly a synchronization time.

The first four variables required the operator to perform a set of about two dozen steps, in sequence.  This was difficult to train, but once an operator got the hang of it, no more complex than setting head-space and timing on a M2 .50 cal.  But the synch time proved a troublesome in practice.  By default the radio reset to 00 seconds of 0 hour of 0 day.  Even when set, radios would drift off time.  New CNR practice revived the concept of a single net control station (NCS) or “master” set to the FH/M mode.  When that station broadcast, all radios on the hopset would re-synch time.

But this failed at several levels.  First, since 1940, the Army had brow-beat operators to reduce transmissions.   SINCGARS had a “time capture” mode that would pick up synchronization, plus or minus five seconds.  But this didn’t help where the day or hour was incorrectly set.  Lastly, doctrine called for the use of queue (CUE) and manual (MAN) frequencies allowing operators to “page” the net master.  But typically the NCS was the command radio which rarely had the time to drop out to respond.  In the field, users often resorted to the old practice of synchronizing wrist watches, then setting the radio’s time.

The first generation SINCGARS, using the RT-1439 radio commonly called non-ICOM (Internal Comsec), lacked the internal crypto circuits.  The only place I encountered these was Korea.  We used a special Y-cable to connect to external KY-57 crypto devices.


The second generation, or ICOM, used the RT-1523 radio and put the crypto circuits in the radio. Note the difference width difference between the ICOM (top) and the non-ICOM the photo below.


The early generation were great radios from the hardware perspective.  SINCGARS saw its combat debut in Desert Storm with 1st Cavalry Division, some Patriot batteries, and some USMC users – all told about 700 sets.  According to often cited statistics, SINCGARS achieved a mean time between failures rate of 7000 hours, compared to 200 to 300 for VRC-12 radios.  My personal experience strengthens this statistic.  In 18 months as a platoon leader in Korea, I never had a radio down for repair.  As a mechanized infantry SIGO, I had maybe ten SINGCARS turned in for repair in about 20 months – total.  (Yet on rotations to Kuwait, we’d have fifteen or more VRC-12 radios in the shop at any one give time.)

For digital data transmissions, SINGCARS supported up to 16,000 bps (bits per second). Sounds pale compared to our high-speed internet today, but in 1989, this was impressive.  But data transmission required clean, strong signals.  On good days, a practical transfer speed was 4800 bps over 20 km.  That would support TACFIRE and other early battlefield digital systems.  But demand would grow significantly by 1995.

The main complaint with these radios was, as alluded to above, the timing variable.  As a SIGO, I often rushed out to a “problem” only to resolve the issue by a time hack.   The problem, I feel, was not the hardware but the complexity of operation, training, and perception.  In 2nd Infantry Division, which received non-ICOM in 1989, from the division down the standard was “frequency hop, green” meaning fully secure.  With training, command emphasis, and real-world operations on the DMZ, the radios worked.  In CONUS, we were lazy, citing the need for compatibility with VRC-12 radios, and radio performance suffered.  However in two contingency deployments to Kuwait, we preferred to carry our own PRC-119s instead of using the PRC-77s issued in theater.

Bottom line – SINCGARS were too complex in operation, certainly not “grunt proof.”  Indeed, even the soldiers in the divisional signal battalion had problems learning the system!

Even in advance of the first generation fielding, the program managers pursued better versions of the SINCGARS.  In addition to addressing the time synch and complexity issues, the Army wanted more data throughput.  Those radios, which began to arrive around 1996, were the System Improvement Program (SIP) SINCGARS.  I will discuss those, and the Advanced SIP (ASIP) radios, in the next post in this series.

7 thoughts on “Past, Present and Future of Tactical Radios – Part 8”

  1. About timing issues…even today a lot of units I have tried to contact “over there” have let their radios drift, or the TOC which is on FH master pulls the whole BDE with it, while mine is constantly updated via the GPS so I would get bits and pieces till we all got on the same time or went single channel. Kind of frustrating when you are trying to respond to a TIC.

    1. That’s the truth… Had a whole brigade LFX come to a screaming halt because we were all on ANCD time and the aviators came in on PLGR time. BDE CDR wanted to get in a C2 bird which wound up landing and half the signal company was swarming around for quite a while to get it all sorted out. Ugly. Never had an issue with time and aviators in theater. I was always impressed when they just jumped in on any net.

  2. I vividly recall the good old days when the VRC-12 freq shift would happen at midnight, and always, always, some idiot would forget or dial in the wrong freq. I can hardly imagine trying to get every station in a mech company to operate 4 or 5 variable keys.

    1. Perhaps I should have ‘plained it a bit better. Although you had 5 variables to deal with (compared to three on the VRC-12 – frequency, call sign, and comsec), in the SINCGARS you didn’t change ANY on a daily basis.

      No frequency or call sign change outs at 0000Z.

      TSEC and HopSet were usually good for a month. Crypto keys once a week.

      NetID was done by SOP, so every time you took to the field you read that off.

      Only thing that changed was the time. Now the irony was I could buy a $25 watch at Wal-Mart that kept time +/- a second a month. Yet a $8000 radio could not keep time that well. That was because the radio was always “seeking” updates from the master and resetting.

  3. With respect to the above, it seems to me I recall we were supposed to change MAN and CUE freqs daily.

    Switching from VRC-12 series to SINCGARS was an abortion. Especially for the old guys. They all wanted to go single-channel plain-text. As a new mortar PL, I personally had to set up all the radios in a vehicle, walk back to my truck, send them an ERF, talk them on, and then go to the next vehicle for 6 guns, two FDCs and two HMMWVs just to get out of the motorpool for the first time. Had a nice long talk with the platoon sergeant, and every man in the platoon did the task multiple times as soon as we hit our assembly area. Not happy. On a good note, using ASIPs radios every day in theater, all of the Soldiers do it like it is old hat.

    1. Esli, you are correct, if you are operating an NCS, MAN and CUE were changed. The regular stations, as Brad was alluding to, didn’t have to.

      Your experience with the ERF and loads matches mine. As I mentioned in the post, 2ID placed a lot of emphasis on the transition. I’ll be bold and say “we” got it right. In CONUS we didn’t have the luxury of a master NCS. Further, NTC rotations required SC operations (so they could collect all that radio traffic for AARs among other things). So the attitude was “oh well, SC is fine.”

      I would agree that all the radio nets I worked with in the “latest unpleasantness” have been remarkably free of the timing issues. Personally I chock it up to improved training and Gen Y knowing how to use electronic thingies. 🙂

Comments are closed.