The Humble Field Phone

I am going to step back from the high speed, low drag, radio communications arena to talk about a very basic, simple and low tech form of communications: field telephones. I will also incorporate the SOI from the previous article into the discussion.

Why use field phones? They’re not near as sexy as that new multi-band radio with attached can opener, the new cellphone with multiple app. thingies or the the laptop with the 50 gazillionbit hard drive. The answer is: they’re rugged and secure. Again METT-TC prevails. If you have a retreat area and need semi-permenant, secure, nearly bullet-proof communications that cannot be D.F.’d, and require very little maintenance, then a field phone system is right up your alley.The phone system is somewhat labor intensive both to install and to recover, but it doesn’t take a Rocket Surgeon to design. Basically, you run a strand of two conductor wire from one phone location to the other, connect the phones and talk.

The phones:

Several different phones are available and we’ll start with the TA-1. The TA-1 is a simplex phone, you can either talk or listen but not both at the same time (that would be a duplex system). It needs no batteries since it uses the power from your voice to generate the audio signal through a simple carbon mic. To signal the far end phone, squeeze the built in hand generator on the side of the phone and the receiving phone displays a silent, visual indicator and sounds a buzzer.  The buzzer can be turned off with the volume control dial on the bottom of the handset. This is my preferred phone for use in the Listening Post/Observation Post (LP/OP). The visual indicator won’t give the position away like the ring or clack of other phones,  but it is hard to see at night. With that being said, keep in mind that since the purpose of an LP/OP is early warning, comms usually only go one way, back into the perimeter. If you feel you must talk both ways at night, turn the buzzer as low as possible. To talk, press the push-to-talk lever on the other side from the hand generator. To reset the visual indicator, press the PTT. Range is about 4 miles and the weight is 2.75 lbs. To connect to the phone circuit, strip back 1/2 inch of the insulation on the two line wires and put one under each spring loaded binding post. That’s it, your done.

Things to look for when buying these phone: Rubber insulating boots in good condition over the binding posts at the end of the cord. If you can’t locate any boots, wrap them with electrical tape after installing the wire. If you crank the generator on a wet phone and the exposed terminals are wet, you will most likely get a stout 80 volt shock. (A truly evil mind (John Mosby) can have lots of fun with that). An intact, rubber insulating cap should also cover both the push to signal lever and the push to talk (PTT) lever on the opposite side. The thin diaphragm over both the mouthpiece (transmitter) and earpiece (receiver) should be intact. If you can’t locate suitable diaphragm material, thin plastic (like cheap sandwich bags) will do in a pinch. You should unscrew each plastic cover trim and check that the carbon mic inserts are in place under each diaphragm. If your buying a set, take along a short piece of two lead wire, hook them together and test them out. The phone should come with a metal or plastic container.  A good source of field phones, parts and detailed information is:  http://signalcenter.com/

For tech manuals go to: http://radionerds.com/index.php/Main_Page

The next phone discussed is the TA/312. A very similar, older version of the 312 is the TA/43. Both require 2 D cell batteries (3vdc) to generate audio and utilize a rotary hand crank magneto for the ringdown signal. If you operate the phones with the SSB-22 switch, you don’t need batteries in the phone (local battery), you can use the batteries in the switch (common battery). The audio level in the earphone and the signal are adjustable. The range is 14 miles wet weather and 21 miles dry. The weight is 9 1/2 lbs, so it’s not something you want to tote around in your ruck. The phone wire is stripped and inserted under the spring loaded binding posts at the top of the phone. The 43/312 has a connector for headphones (if you can find a set). The phone should come in a canvas zipper bag. Check for the same carbon mics in the headset. Also check the battery compartment for ruptured batteries. I would use these phones back at my comms center and in more permanent, built up fighting positions. You can also install a dial tone (DTMF) keypad adapter module to the 312 for use on plain old telepone service (POTS) lines.

As an added note, if you don’t have a lineman’s butt set; when we were in the field and could find a telephone pedestal, I have seen these field phone tied into the pedestal using alligator clips on one end of a short pair of field wires. The alligator clips were moved to different pedestal punch down connections until a dial tone was heard in the headset. Then the hook switch on the phone was clicked in the phone number sequence with short pauses between the numbers, to simulate the old rotary phone dialing clicks and a phone call would be placed. I just saw it happen, because …….I would never do that myself. Yeah, that’s how it went……

Used German Army model FF53M field phones are also in common use. They can be picked up at Army Surplus stores and online. Ours use two D cell batteries, but I have heard of models that use five AAs. Again, the batteries supply audio power and a hand cranked magneto is used for signaling. The case is black Bakelite. They weigh 9 1/2 lbs and have a listed range of 16 miles. I have not tested to see if the German phones are compatible with the U. S. phones but I assume they would. I know….anytime you assume it makes an ass out of u and me.

Switchboard:

The SB-22 Switchboard is used to connect up to 12 phones back to one location in a star configuration. I would use this in my central comms room at the BDOC. Then the phones can be patched together by the switch operator. Attach each set of wires to the modules under the back cover of the switch. Label the wires and label the matching tag above the appropriate patch cord. When a call is received, the appropriate lights will appear as well as the audio signal. The operator then picks up the call based on which indicator lights up.  He then places a call to the other party and patches them together. When they hang up the indicators go blank. It uses 4 D cells for audio. The switch has a signaling crank on the front. It requires a special headset with boom mic to operate, but if it is missing, you can substitute a field phone wired into the back with the matching patch cord inserted. With additional modules you can connect military radios and other devices into the system.

 

Field Wire and Spools:

The two basic types of wire are the wd-1 (two twisted, individually insulated wires) or the WD-1A ( two insulated wires bonded together). Each has four copper and three galvanized steel strands twisted into one wire with a tensile strength of 200 lbs.  You can also find 4 pair and 26 pair cable. The wire weighs approximately 62 lbs per mile.

The DR-8 is the smallest and lightest of the military spools. Ir contains 1/4 mile spool of twin lead wire. Notice on the side of the spool two insulated connecting terminals with a small insulated hole beneath each. These are used to connect the free running ends of the wire on the spool to. Then you can later wire your phone directly to the spool with the remaining unused wire left on the spool. This saves cutting your wire into short pieces over time. A hand or chest mounted reel called the RL-39 can be used to play out or reel in the DR-8 spool.

Wire spools and reels come in many larger sizes up to the DR-5 which will hold 2 1/2  miles of 2 conductor wire. It is used with the RL-31 Reel. We used the RL-31 in the back of military and civilian pickups, jeeps and HMMWVs to reel out miles of wire.

Procedures for installing a field phone system.

As listed in the SOI, our retreat has two, two man fighting positions (bunkers) with overhead cover and two LP/OPs (Listening Posts/Observation Posts – the LP/OP’s are not heavily fortified positions, they are instead well camouflaged positions with minimal cover that provide early warning of approaching forces. Listening at night, observation in the day.

The primary comms to our bunkers from the Base Defense Operations Center (BDOC (pronounced bee-doc)) consists of two sets of field phones. One set to each occupied bunker. The same for each occupied LP/OP. The east LP/OP phone is connected directly to the BDOC. The other LP/OP is about 100 meters north of the north bunker and that LP/OP phone is connected directly to another dedicated phone in the north bunker.

So we have a total of 3 phones at the BDOC. One to each of 2 bunkers and one to the east LP/OP. The north bunker has 2 phones, 1 to the BDOC and another to the North LP/OP. For a grand total of 7 phones. You could eliminate 3 phones at the BDOC is you could manage to scrounge up an old SB-22 switch board. You could also wire all the phones together in a “hot loop”. Then if you signaled with your phone using the hand crank, all the phones in the loop would ring at once.

We use one spool of standard army WD-1 wire on a 1/4 mile DR-8 spool for each circuit. When running each circuit, a stake is driven into the ground, near the phone, to loosely tie the wire to. Tying the wire down prevents someone from inadvertently tripping over the wire and pulling all your phones onto the ground. It also provides an anchor point for your reels when you play the wire out. Enough slack is left at the stake to run the free end of the wire to the phone. The wire is then spooled out from each position to the BDOC , where it is again wrapped around a stake. The wire at the spool end is not cut, but the free running end should be running out of the hole at the center of the spool and connected to the terminals on the spool. Then a separate section of wire is also attached to the terminals and the phone, completing the circuit. The spool is left at the BDOC to allow personnel to quickly roll the wire back up toward the far position. Or in an emergency, the wire can be cut at the spool, and the remainder of the wire on the spool is saved.  If the bunker or LP/OP  is not manned, the phones are disconnected and returned to the BDOC while the wire is left in place. When relieving a sentry, I have used the tied down commo wire to find my way to a position at night with no illumination. It’s probably a good idea to call and give the sentries on duty in the position a heads up prior to using that trick at night. Sentries usually physically check the wire once a day for wire taps, cut wire and attached booby traps. This is known as “walking the wire”. Each time a phone is attached to the wire a test call is made to the BDOC. A unique colored plastic wire tag is attached to each set of wires running from the BDOC to the individual positions. While tags can be attached to each end of the wire if you have multiple phones at each position, in our example we will only tag the BDOC room end. The tags are colored as per the SOI in the previous article. Radio procedures do not apply in a field phone circuit, just use common sense. When we picked up the phone for a call, we usually said something to this   effect: BDOC or Mortar Pit, West Tower, Motor Pool, etc.

One last note, if you don’t have access to military field wire, just about any wire will do in a pinch. If it’s TEOTWAWKI, you could use phone line wire. Speaking of phone wire, there is a inexpensive device known as the Ramsey QLRD1 Automatic Telephone Ringdown that will allow phone calls over dead copper phone circuits. Say from your house to your neighbor’s. You will need one device for each end and a 12 volt power source, like a car battery. Plug the phone in and when you pick up the phone it will ring on the other end. It won’t send the signal through a SLIC where the signal is converted from analog to digital. If the power is down, then the SLIC is down. Something else to ponder.

DOL

Dan

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