Other Field Expedients

A collection of field expedient stuff, electronics and otherwise:

Improvise, Adapt, Overcome

(Also see field expedient antennas in the Antennas sections)
Field Expedient Antennas

Field expedient keyer paddle:

To go along with my quickie HF mobile installation I needed to make a simple, lightweight keyer paddle for CW. The station Vibrokeyer paddle is too big, heavy, fragile and expensive for this application. More junk box parts:

Some tapped brackets, a chunk of plexiglass, stick-on rubber feet and a hacksaw blade starts the design. A few terminal lugs, a stereo cable and plug plus some heat shrink tubing and it’s ready to go. I used anti vibration nylon-insert machine screws for the contacts but you could just use simple jam nuts to keep the screws from backing out.  Also, you don’t need “jeweled bearings”, or anything else fancy.  I keep the contacts just a few thousandths spaced;  blade barely moves. Doesn’t slide around and there is room for a hose clamp to attach it to the bottom of the radio in the mobile.. Cost? Again, Zero.


Field Expedient Fuse Repair:

Yep, sometimes necessary.  Especially if your gear does not have an emergency Battle Short Switch to bypass the circuit protection under battle conditions like some of the big Navy transmitters have.  Many pieces of older military comms gear use the large AGU – type fuses in the low voltage primary circuits. Those include the GRC-9 dynamotor supplies, RT-68 PP-112 systems etc. The AGU fuses measure 1.5 X 0.4 inches diameter.  These are typically rated for 32 volt service and have a lower voltage drop than, say, a fuse rated for 125/250 V service.  But those large AGU fuses are getting harder to find at your local auto parts store – particularly just prior to your next field-op.  What to do?

I needed a 4 Amp fuse for my VRC-7/RT-70 mobile system.  It is the fuse in the front panel of the AM-65 amplifier chassis that powers the system.  I reasoned that a standard automotive AGC 3AG 32 volt fuse (1.25 X 0.25 inches) should fit INSIDE the larger fuse if I could drill out one end of the blown fuse.  The glass tube has an inside diameter slightly larger than 1/4 inch.  Using a size F drill bit (0.2570 inches), I carefully drilled a hole in the end of the dead fuse and then used a Q Tip to remove the vaporized metal from the blown fuse wire.  You could use a standard 1/4 inch drill bit but you may have to enlarge the hole slightly for a clearance fit.  Be careful not to break the glass tube.

I then cut a small segment from a junk-box spring and loaded it into the AGU fuse and then inserted a 4 Amp, AGC fuse inside the larger fuse – perfect fit.  The spring serves to improve/define the contact with one end of the fuse and also pushes the AGC fuse out sufficiently so you can grab it with pliers to replace if necessary.  (You DID clear the fault that caused the fuse to blow in the first place, didn’t you?)  The fuse holder cap captures everything and the holder socket spring properly compresses the whole assembly. A small wad of tin foil would make a field expedient spring in a pinch.  (nested field expedients?)

Field expedient fuse repair N6CC

Repaired fuse assembly N6CC

“But Billy-Bob, I usually just use a .22 Long Rifle cartridge; they fit into my truck’s fuse clips just fine”

Works great. Presto!  Back on the air.


Here’s another handy item:  The Check Engine Light

Neon Check Engine Light

This is a simple way to verify that the ignition system is working when off road in the boonies and something stops.  Just zip-tie an NE-51 neon pilot lamp to the HV wire between the coil and distributor cap.  Solder a wire from the lamp tip and attach that to engine ground.

The electric field around that wire when the pulse occurs (points open) is sufficient to ionize the gas in the lamp producing an orange flash – with each ignition pulse.  Simple, effective, works great.  I also used these on dirt bike ignition systems for a quick operation verification.

Then there is a field expedient when you need an “FT-243 crystal” but only have some HC-49 wire-lead jobs:

FT-243 Crystal Holder hack

A little work with a Dremmel tool makes it happen. Not all FT-243 holders have identical internals so some may need more “excavation” than others. In any case, easy enough.

These HC-49 “hacks” usually operate a couple of hundred cps lower than the marked crystal freq since the FT-243 circuit generally provides a 32 pf load capacitance and the HC-49 spec requires an 18 pf load. So it oscillates slightly lower than expected. Usually not a problem in old military rigs on CW or especially AM.

They can be tweaked back to the marked frequency with a small capacitor in series to bring the external load down closer to 18 pf. A small variable cap in the radio works for me. Take a look here for how I implemented that in a crystal controlled AN/TRC-77 transceiver:
AN/TRC-77 modified for HC-49 crystals

HC-49 crystal in an FT-243 holder

Field Expedient Refrigerator: For dire emergencies….

Field Expedient Refrigerator

The great ALICE Pack & related:  Some common sense stuff:

The great ALICE (All purpose Light Individual Carrying Equipment) pack is my go-to bag for Bush Ops or even general purpose travels.  They are hard to beat and this one has served me well for a long time.

Like most USGI gear they don’t really need any significant improvements or modifications, they are tried and proven.  Maybe some very simple additions if you like:

ALICE Pack carrying handle

An obvious improvement for just moving the bag, off-shoulders. Soft vinyl tubing, 550 cord through the LC-2 strap loops. Or another one when just using/moving the frame for carrying radios or other cargo: Simple.

ALICE Pack Frame handle
ALICE Pack Frame handle

Another simple preparation is to water proof the inner side of the top flap compartment. The original rubberized inner coating has since worn off rendering the bag contents vulnerable to rain. Some guys use Flex Seal on the underside of the flap which is a good idea.

ALICE Pack Scotch Gard Water Repellent

Flex Seal works OK but what about the contents of the Map compartment under the lid? I prefer to just hose down the top/outside with Scotch Gard – keeps your stuff dry but also protects the maps in the pouch between the flaps. Better.

Here’s another obvious modification to the cinch straps. The issued straps/buckles work fine but are impossible to open with one hand and you sometimes have to entirely remove the straps from the buckles to load the bag. Here is a better way that still allows one to use the original buckles if necessary.. If you only make one “Mod” to the bag, do this one:

ALICE Quick Disconnect Strap Buckles
ALICE Quick Disconnect Strap Buckles

The above are the type with the removable steel loop-pin. You can attach the female end to the bag without cutting or sewing the fixed web loop. Simple. REI has them.

Simple one-handed unbuckling

One-handed operation to unbuckle. Then the entire strap then clears the top of the bag for loading/unloading. The orange tag is to ID mine among a pile of others on the Tarmac.

Here’s another simple improvement to the USGI Stainless Steel canteen: Removable cap via a fishing snap swivel chain clip.

Fishing Snap Swivel on Canteen Cap

The above allows you to heat the canteen directly in/near a fire without melting the bakelite cap. I prefer these stainless steel canteens to the newer plastic ones: They don’t take on the taste of the last liquid you had in it and you can heat these directly in/near a fire. A little heavier, would be better with a wider mouth (for packing with snow etc.), but Embrace the Suck, they are worth it.

Speaking of chow, here is a good trick going back to WWI to “lock” the handle of the USGI mess kit pan. Keeps it from flopping around on the hinge while cooking something.

As we know, the USGI Mess Kit was not made for cooking per-se. It was made for standing in a field kitchen chow line to receive A or B Rations.  Like everything else USGI, including the essential canteen cup, this gear is versatile.

Mess Kit Pan Handle Stiffener

A really handy helper. Carved, notched stick wedges in tightly between the hinge and the far end of the handle. Makes for a solid handle while heating or pouring stuff – no flopping around and dumping your chow. Perfect while making Battalion Landing Team (BLT) sammitches.

USGI Frying Pan Handle Stiffener

Above:  My kit is a mongrel – the pan is stainless steel, the plate is aluminum.

Improvise, Adapt, Overcome!