Continuing from Part 3 – In the last segment I was perhaps a little brief with the overview of post-Korean War vintage radio sets and explanation of the different working FM format bands. Semi-officially, the 1950s era radio sets were known as the GRC-3 series, after the primary armored vehicle radio set. Rather than another 1000 words, perhaps a diagram for reference:
The diagram references the four (arguably just three with an overlap) bands, the base radios used on each band, and the radio sets issued. Base radio designations for receiver-transmitters (RT) and auxiliary receivers (R). For a more detailed component listing, please refer to Green Radio’s excellent technical breakdown.
Let me stress three points about the different bands. First, the “platoon” band was for the most part an overlap of the “infantry” band. Second, the reason for these separate bands goes back to the technology. The radios of the day still used crystals with limited range. To reduce the operator’s workload (and part inventory), the Signal Corps opted to “build in” crystals with specific frequency ranges. Which leads to the third point, these specific frequency ranges assumed that radio traffic could be segmented by combat branch to some degree.
However, this certainly did not mean that only infantry units operated on 38 to 55 Mhz, or armored units were restricted to 20 to 27.9 Mhz. Instead, the Signal Corps’ intent was to issue equipment based on the need to operate on certain communications networks. For instance, armor units often used the AN/GRC-3 which included an RT-70/GRC radio offering access to the infantry frequencies allocated to platoon and squads. Clearly this required a lot of radios, operated by a lot of radio operators (recall, 9% of the battlegroup strength allocated for communications personnel – wire and radio). And one can imagine a number of scenarios where these different bands on different radio sets might offer an impediment to information flow. While certainly better than the setup used during World War II, the GRC-3 series was still cumbersome in operation (not to mention a nightmare for the property book officer with no less than 24 component lists!).
By the early 1960s the next major leap in radio technology arrived to solve some of these ills – the first solid state semi-conductors. Transistors first became practical in the late 1940s. By 1954 the first transistor based receivers became the “hot” item on the American commercial market (There was no DARPA at that time, remember). Within a few years, the Army began testing transistor-based radios with an aim to replace the GRC-3 series. This project lead to the AN/VRC-12 series and the AN/PRC-25/77 family of radios.
Now we often think of things that go boom when referring to “classic” military equipment. Yes, M-4 Sherman tanks, M-113 APCs, P-51 Mustangs, F-4 Phantoms, and I’ll throw in the Iowa-class battleships as examples of long serving, battle-tested “classics.” Well I’d submit the VRC-12 family (including those PRC radios) are also “classics,” although without the boom. How good were these radios? Well after entering service in the early 1960s, the sets hung around in the inventory until just recently.
An Army training video from the 1960s expresses the virtues of the system rather well:
For those who can’t watch this captivating 27 minute clip :-), I’ll touch on some high points:
- Radio set configurations based upon two types of receiver-transmitters (RT-246 and RT-524) and one receiver (R-442). Outside scope of video were the PRC-25/77 and associated vehicle mountings.
- Frequency range from 30 to 76 Mhz, divided into lower (30 to 52 Mhz) and upper (53 to 76 Mhz). Not discussed in the video, this because of the need for two separate tuners, still a technology limitation, but with miniaturized circuits, easily overcome.
- The VRC-12 series effectively dumped the “armor” band and part of the “artillery” band, but expanded into the cleaner high range frequencies.
- The VRC-12 offered 920 channels, over 350 channels cumulative between the radios of the GRC-3 series.
- Dispensing with the separate bands, if the operating frequency was known – say by browsing the Signal Operating Instructions(SOI)- any radio operator could tune into any net the mission required. In theory from corps commander down to the individual squads.
- Weight of vehicle mounted radios reduced to 100 pounds, with space needed down to 1.2 cubic feet.
- Power out increased to 40 watts maximum, with range now reaching to 30 miles.
- Simplified maintenance due to completely modularized construction. Components supported “go or no-go” testing (a really big advantage). However, note that while the new radios featured 100 transistors, the system still relied upon eight vacuum tubes.
- Support for facsimile transmissions. Yes, very seldom used, but foreshadowing the use of data systems of today.
- Improved noise reduction with new squelch techniques. However support for legacy squelch formats lead to operational issues later.
- Tuning of the VRC-12 was simple – just turn the knob.
- Briefly discussed, the VRC-12 series required “cutting” or matching of the antenna. This required operation of a mechanical switch underneath the antenna matching unit, either automatically via a cable from the radio or manually by the operator, to the corresponding resistance level.
The early prototypes of these radios came out in the late 1950s. Although production started around 1961, few were issued prior to 1964-5. For reference, this chart details the components of the VRC-12 and PRC-25/77 family.
With the introduction of these “solid state” radios, the Army had solved some of the issues facing communications at the tactical level. However some issues remained unaddressed. I’ll go into this in more detail later, but the PRC-25 evolved, with the addition of new features, into the PRC-77, thus the different designations.
- Range extended out to 30 miles (vehicle mounted) or 5 miles (backpack)
- Use of solid state, modular components, with minimal vacuum tubes.
- Backpack radio weight reduced to 14 pounds and vehicle radio to 100 pounds.
- Pack radios continued to use heavy, short duration, batteries.
- Technical aspect of operation reduced to frequency, power, and squelch selections (and a few other options) using front panel knobs.
- Still vulnerable to jamming, but new squelch feature greatly reduced natural interference.
- Interception still a threat, and only mitigated by use of SOI based challenge-authentication and manual encoding.
- Improving voice quality.
- Increased number of channels, along with single frequency band, reduced command net congestion to some degree.
Across the board improvements came with the VRC-12 series. The type saw a long service life in the US Army, from Vietnam to beyond the Gulf War. And the type remains in use around the world. In my next installment, I will look at that service, particularly the backpack radios. Along the way I’ll consider wartime experience and evolving tactical doctrine, and point out what issues prompted the Army to start looking toward digital radios.