MilCom

First of all, "My Bad!" It has been months since I have blogged anything and I must apologize to the readers of this blog. I have three other entries in draft and will get this posted ASAP.

Over the years I have collected, restored, used and sold a lot of old military communications (MilCom) equipment. It started when I was in high school when a family friend gave me a beat up BC-1000, low band FM squad radio circa WWII.

That led to a slew of old ARC-5/Command Sets (mainly receivers) and the occasional piece of test gear. My 20 year career in the USAF allowed me to "play" with a lot of comm gear but due to constantly moving around the world precluded my obtaining any surplus gear. 

The one exception was when I was assigned to the 1936 Comm Squadron in Lajes Field, the Azores. The folks at AFR&M surplussed out a bunch of old Motorola base stations in the low band and high band VHF freqs. I purchased a L43GGV high band radio that I (along with several others) converted over to 2M FM....146.94 simplex and 146.34/94 repeater frequency. 

Once I was transferred to the 3rd Mobile Combat Comm Gp (3rd MOB) at Tinker AFB, OK (right outside Oklahoma City) I became active on the local 34/94 machine with my 20 year old Motorola rig. Thank you Uncle Sam.

Once I retired from the AF in 1987, I found that MilCom gear tended to follow me home from various ham radio flea markets. Prior to moving from PA to GA I had a basement full of military comm gear, most of which I realized that I was never going to restore much less use. Therefore, I sold off about 90% of my MilCom gear. 

A couple of Command receivers, a BC-221 frequency meter, a GRR-5 SW receiver, and my favorite: a PRC-74B HF synthesized SSB/CW transceiver followed  us down to GA. Within a couple of years those were also sold off due to the need to get some liquid funds after our move. 

The PRC-74B (also called a "74 Bravo") was my retirement present to myself. Mark Francis, KI0PF, built this radio up from spares that he had accumulated and installed the LSB mod to allow both USB/LSB operation. Designed and built by Harris Corporation, the 74 Bravo was the first fully synthesized HF radio to see service in military ground forces. Used primarily by the Army Special Forces (Green Berets) in Vietnam, this provided the special ops folks in country with reliable HF communications. I really hated to sell that set as it had special significance for me but hey, when the wolf is at the door.....

Slowly (very slowly, actually) I began obtaining the occasional small piece of MilCom gear. One of my all time favorite low band VHF FM squad radios is the PRC-1088 manufactured by Datron. Originally Rockwell Collins designed and produced this man-pack radio set to enter the completion to replace the venerable PRC-77 from the Vietnam era. Unfortunately the military declined the Collins radio in favor of SINGARS. Rights to produce this radio were sold to Datron which still produces it today. It is a nice FM unit with a digital readout that can frequency hop while offering an optional encryption package for secure voice communications. Mine hops but cannot go secure. The overall package is the same form factor as the PRC-25/77 and uses the same mics, speakers, and headsets. The antenna connector is a BNC type unlike the PRC-25/77 radios. It offers low power output of around 300 mW and a high power output of around 7W. 

During a recent flea market run my wife, Patricia, (KB3MCT) and I found an estate sale that included a large amount of MilCom gear that covered WWII to Vietnam. I was too late to pick up one of the two PRC-74s, but was able to score four Command receivers covering from 100 kc to 9 mc. Three of these receivers were installed in a triple receiver rack and included the remote tuning and audio units and all the proper wiring. Unfortunately no splined tuning shafts but all the receivers had tuning knobs in stalled so it was no biggie. 

One BC-312 WWII HF receiver followed me home along with two PRC-127 hand held low band FM units theoretically used in the first Gulf War. They worked, too!! 

The US Army Special Forces during the Vietnam era needed a portable low power HF set to provide intermediate range comms in the jungle. Sylvania was chosen to design and field such a radio and the AN/TRC-77 was born. This luggable radio set. while it was portable, was not able to be operated in a man-pack configuration and therefore was given the TRC (Transportable Radio Communications) nomenclature as opposed to the PRC (Portable Radio Communications). The 77 was a CW only (on transmit, CW/SSB/AM on receive), six channel crystal controlled package about the same form factor as the PRC-25/77. It was tested over a period during the early 1960s but was not adopted by the Army for use in Vietnam. However, the LRRP (Long Range Recon Patrol) units in Europe utilized this radio for HF comms finding it fitting their needs as long as the operator was a good CW op. Operation is ultra simple, the six channels can be independently selected and a set of "cans" and a key (antenna not withstanding) are all that is needed to get on the air. 

The TRC-77 soon became the 77A with some minor internal and external changes. But in essence it was the same radio, same size and still very easy to operate. Those of us who like to obtain, restore and use MilCom gear find the 77A a great little rig with a price tag that is fairly easy to swallow. Mine cost $200 with no crystals. 

Crystalling up one of these radios is expensive today. With the demise of International Crystal Manufacturing (ICM) there are only a couple of crystal providers and their prices START at $50/each, depending upon the type!  However, there is a work around. Digi-Key carries a series of crystal oscillator ICs that are extremely stable and come in 8 pin DIP through-hole components. Hayseed Hamfest offers a four-IC PC board in kit form that will provide four independent oscillator outputs that can be used in older radios. This board seems a bit large for inclusion inside the 77A but the idea of using these programmable IC oscillators to replace crystals in older radios has merit. Besides, it a whole log cheaper! 

There are also options to rock up the transmit side of the 77A using HC-49 crystals (with leads) obtainable from QRP.ME and
expandedspectrumsystems.com. Prices are very inexpensive and these crystals can be directly soldered to the underside of the transmitter crystal bank and they will work quite well. (See N6CC.com for details on all this crystal stuff.) 

The receive crystals are 455 kc ABOVE the transmit frequency which makes it basically impossible to use QRP HC-49 crystals for the receiver. This is where the programmable IC oscillators will shine. Again, consult N6CC's website for intimate details. Tim has done a lot of the heavy lifting on a number of MilCom restorations and modifications so he speaks from first hand experience. 

I am going to detail the restoration of my 77A in this blog, hopefully spiking some interest in others to quit building "cute" little single band kit CW rigs and move onto some REAL radio!!! 

Vy 73

Rich K7SZ