From the Collins Reference Library:
Note from Dave Ross: “The images presented here are from Jim Stitzinger’s “Collins Reference Library” in Valencia, California. Many thanks to Jim for letting me have copies of them.”
As far as radios were concerned, the WWII-era had been the time of CW and AM modulation. These modes of modulation quickly became inadequate to serve the needs of the post-WWII military. Collins engineering capability and penchant for studying effective communication prevailed and the Single Sideband era (SSB) was born.
All photos are courtesy of the Collins Reference Library and were captioned by the late Dave Ross. Thanks go to Brian Bjerkelund, k7ais, for allowing us to present this information.
Here is a 718U-2 (AN/VRC-80) in a different M151 jeep. The 718U-2 is also a 400W HF radio, again built using URG-2 slices. The -2 version uses a separate 671U-1 receiver/exciter, which is shown next to the radio case and in front of the jeep’s rear seat. Note that, with the separate 671U-1 receiver/exciter rather than an internal 671U-4A receiver/exciter, the 718U-2 main radio case is narrower than case on the 718U-2A pictured above. All the 718U-2 variants use the same power amplifier module & power supply module & antenna coupler case.
Another photo of the 718U-2 with a better view of the 671U-1 receiver/exciter. The 671U-1 receiver/exciter is also part of the 718U-1, where it is paired with the 100W 548S-1 PA/coupler. The 718U-1 was sold to the U.S. military as the TRC-169. The TRC-169 came with a rucksack frame for use as a manpack, where it was powered by a BB-451 silver-zinc battery. The TRC-169 also had facilities to mount in and be powered by a vehicle.
Here is a 718U-2A (AN/VRC-81) in an M151 jeep. The 718U-2A is a 400W HF radio, built using URG-2 slices. This -2A version uses a 671U-4A receiver/exciter, which is inside the larger of the two watertight cases. The control head is shown mounted on the transmission hump, and the driver’s seat has been removed so it would be visible from this camera angle. There is also a 718U-2B version of this radio and as far as I can tell the only difference between the -2A and the -2B is the type of frequency selector – either knobs or levers. The M151 jeep itself is apparently owned by Collins and probably makes the rounds to all the trade shows carrying various radios.
The mounting plate is a simple affair and attaches both the radio case and also the antenna coupler case to the jeep. It looks as if the antenna coupler case was specifically designed with a corner missing so that it the radio install would not require removal of the rear seat. It’s a bad idea to have the antenna coupler sticking out further than the jeep’s bumper, especially considering that the radio costs about 10X what the jeep costs…
USMC 329413 is the hood number on this jeep, possibly it was loaned to Collins as “GFE” – Government Furnished Equipment. All the 718U-2 variants use a 548T-1 RF power amplifier and a 636X-2 power supply – the supply operates from +28VDC generated by the jeep’s alternator. In a 718U-2, the PA & PS are inside a 718F-7 case, and in a 718U-2A the PS & PA are in a 718F-8 case along with the 671U-4A receiver/exciter.
The antenna coupler used in these 718U-2 radios is a 490B-4. What’s inside the waterproof case is just a 490T-2, which is nothing more than a 490T-1 with a fan. The whip antenna is an AT-1011/U – a 32’ fibreglas whip – looks like only the bottom 16’ was in use for these photos.
Here’s a photo of the MRC-83 production floor at Alpha near Dallas, Texas. In the foreground is an M38A1 with a TRC-75 1kW HF radio installed, the radio is under a protective wrap. Behind the first jeep is another, the radio is visible but has it’s front watertight cover installed. Third jeep ditto, fourth jeep ditto. Lower left is a jeep that looks to be in the middle of an alternator install. Middle left on the floor appears to be accessories for the MRC-83 in a cardboard box banded together with an AT-1011/U in it’s canvas case. visible at the top of the photo are four TSC-15 “Communications Central” radio shelters, shown with their vent covers open.
Still at the Alpha facility, here’s a teamster type driving the finished product up onto a car transporter. Note that the TRC-75 install really flattens out the rear springs in the M38A1.
Here are three unique manpacks – a 719D-2, a 719D-15, and a PRC-105 in a vehicular mount. The 719D-2 is sometimes called a PRC-515 or an RU-20 – it is a 20W HF transceiver which is powered by a NiCd battery pack. The 719D-15 is the big brother of the 719D-2 and is about the only instance where the suffix of the Collins model number means anything in the real world – the 719D-2 is a 20W radio and the 719D-15 is a 150W radio. Both use the same receiver/exciter & control head, but the -15 version has a much larger PA/coupler unit and is powered by a BB-451 silver-zinc battery. The PRC-105 is a strange beast – it uses a Collins-built power amplifier & antenna coupler unit, but has a Hughes-built RT-1209/URC receiver/exciter. Must have really frosted Art to have to build the PA/coupler and not sell his own receiver/exciter with it. The PRC-105 was intended as a 100W manpack – it too is powered by a silver-zinc battery. The PRC-105 shows up in PRC-104 marketing literature from Hughes but Hughes doesn’t mention the origin of the PA/coupler unit.
Publicity photo of a complete MRC-83 radio set, a TRC-75 installed in an M38A1 jeep. Visible underneath the radio is the power supply box carrying the PP-2352 inverter – the inverter runs off 28VDC and makes 115 VAC 400~ 3 phase power for the radio. On the front of the power supply box are controls for the inverter and also a rudimentary selftest setup for the inverter with lamps to give a go-nogo indication as to the health of each chopper transistor in the inverter. The MRC-83 first saw the light of day around 1960 – in those days it was quite a feat to put a 1kW automatically-tuned HF radio in a vehicle. I saw over 2000 TRC-75 radio sets come up for disposal at DRMO Barstow in the early 1990s, and I guess that most of those radios were installed in M38A1 jeeps just like this one – the 1960s was an excellent time to own stock in the Collins Radio Corporation.
This appears to be some sort of MRC-108 prototype built in an M38A1 rather than an M151. Visible is the 618T-3 box & control head, with a PRC-41 with rucksack frame on top for UHF AM coverage. To the right of the 618T box is a PRC-47 with cover attached, and on top of that is the rear of a PRC-25. There is plenty of room on the M38A1 floor, underneath the 618T box and the PRC-47 and it looks like there are other radios under there, probably another UHF aircraft AM radio and also another VHF vehicular FM radio. The PRC-25 & PRC-41 & PRC-47 are probably meant to be dropped off and operated ‘on the ground’.
Another photo of the same M38A1 with MRC-108 electronics, this one with the canvas top attached and the vehicular UHF AM antenna erected.
This looks to be an early MRC-108 in an M151, there is a 400W HF SSB radio using a 618T-3 with an 850 CPS teletype modem and 115 VAC 400~ inverter in the box on the right sponson. Usually a Kleinschmidt TT-4 sits atop the 618T-3 case – it is not present here. A 180R-6 antenna coupler is in the case on the left sponson. Since there is a UHF antenna on the jeep, I assume there there is more radio gear in the jeep even though it is not visible in this photo.
This is a VC-120 installed in an M151 jeep. The antenna is an AT-1011/U and the base looks like something created by the engineering department just for this photo shoot. The VC-120 is also known as a GRC-220, this one apparently has an early power conditioner, since the more common power conditioner units have the speaker on the left side of the front panel. The antenna post on the radio will accept a 15’ whip antenna (like that used on the PRC-47), and the radio can be powered by a BB-451/U silver-zinc battery (like that used with the PRC-47) – the manpack version of this VC-120 radio is called the MP-150 or the 719D-15. Looks like the antenna post is jumpered to ground but the ANT SEL switch is still in the WHIP position, doubtless a radio silence precaution taken by the Collins Marketing ‘droids.