Summer 2006 Issue


Fun with VHF—MilCom Equipment

By Rich Arland, K7SZ

Sometimes we tend to forget that amateur radio is a hobby, something to have fun with. All too often we collectively take ourselves way too seriously. With this in mind, this column is dedicated to having some fun with VHF. Along with the fun we will hopefully entice some of you to try something a little different in the radio hobby—a road less traveled, if you will, but filled with rewards nonetheless.

If you have been reading this column since the beginning, you will remember that your author (that would be me) has an extensive military background. Having spent 20 years in the U.S. Air Force in (what else) Comm Command, I have had a lot of experience with military communications (MilCom) equipment. Only within the last several years, though, has the bug bitten to start obtaining some of this classic military radio gear and use it on the air.

Now I know what you’re thinking: Military gear smells funny, is a nasty shade of green, is big and heavy, takes funny voltages and weird connectors, and isn’t very easy to work on when things go wrong. Well, the vacuum-tube and solid-state military equipment is basically no different than any other commercial vacuum-tube and solid-state gear as far as voltages are concerned. Of course, how the military power supplies develop those voltages can be somewhat convoluted, depending upon dynamotors (huh?) and vibrator power supplies (say what!)

Well, the good news is that these power supplies are readily available on the used market, and since they are extremely rugged and relatively easy to repair, seldom will you have to do any troubleshooting in order to make things work. As far as connectors are concerned, they are also available from various sources at reasonable cost. Concerning maintenance, a little known fact among non-military folks is that the Technical Manuals (TMs) and Technical Orders (TOs) are written on about a sixth-grade level and are very detailed, including extensive troubleshooting information. OK, the smell: That is an anti-fungal shellac that is sprayed on the older military gear (WW II through Viet Nam era equipment) and many of us “Green Radio Guys” actually love the smell of the gear! Hey, one snort of that stuff and you know you have your hands on a piece of “real” radio equipment! As for big and heavy, yes, some of it is, but that is due to the stringent engineering that is needed to meet military specifications (mil spec) and survive in combat. In short, you can’t really go wrong buying and using MilCom gear if you have the TM/TO for each particular piece of gear you own. There are many sources of TMs and TOs, so finding the right tech info is a no-brainer.

This is the venerable RT-70 transmitter/receiver (middle) coupled to its 24-volt power supply/audio amplifier, the AM-65. The loudspeaker atop the RT-70 is an LS-166, which is common among most MilCom units of this vintage. This set was used from the Korean War well past the Viet Nam era by the U.S. military in jeeps, trucks, command posts, and about anywhere tactical VHF FM voice communications was required. The RT-70 is connected to the AM-65 by spring clips on the sides of the case. Power to the AM-65 is accomplished by a cable in the lower left socket. The voltages necessary to run the RT-70 along with audio transmit and receive are coupled between the two units via a “dog-bone” connector on the right side of the radio/PSU. This unit weighs in at arond 35 pounds.

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