Ammo Box Radio !

UPDATED 3/14/16

Did you ever have a need for a particular piece of Military surplus equipment – only to find the Military never had such a device?  Much less “surplussed” it?  Seems I run into that occasionally so the remedy is to build my own.

Standard US Military ammunition “cans” are great for storing and transporting almost anything that will fit inside.  Strong, watertight and available, they are also great for building “Military Surplus” electronics inside.

In 1969 I wanted to build a portable transmitter that covered the 80 meter CW band utilizing a VFO.  So I designed a 2 tube rig running a 6AU6 oscillator in a Colpitts circuit driving a 6DQ6 TV sweep tube amplifier.  It runs about 450 volts on the plate from a built-in power supply and an OA2 voltage regulator for the oscillator; the whole transmitter is powered by 120 VAC.  It was mostly built from parts scavenged from old TV sets because my neighbors thought I liked to “play” with them.  After looking inside 45 years later, I am surprised it worked, so a little “rebuilding” is in order to clean it up.  Here is a shot of the original transmitter built inside my first Ammo Can.

Sometime later I needed a tactical COMMINT receiver for training purposes. It needed to be simple, sensitive, rugged, water resistant (and cheap). I couldn’t find anything I liked (or could afford) as “Army Surplus” so I took an old Bearcat 210 scanning receiver and rebuilt and repackaged it. I included an S-Meter, a squelch-operated relay to turn on an external cassette tape recorder and a few other improvements. It includes provision for an external antenna via the panel BNC and also a provision for the S-Meter to measure the internal battery voltage. I needed it to work from either 120 VAC power, external 12 VDC or an internal PRC-25/77 battery BA-386 or BA-4386 my Navy Reserve unit used. I made an external connector for a PRC-25 goose neck spring and tape antenna as shown here.

Built inside an ammo can, the result was quite successful and used for many years in the field and at home. The external cassette tape recorder sits still until a carrier appears, then the tape starts and audio is routed to the recorder Mic input. Very useful in collecting “intel” but also in debriefing training exercises with our comms people. I called it the “AN/PRR-1″. This radio has been to some interesting places around the world. See photo below.

Sometime later yet, I got a GRC-9 HF transceiver but not any of the power supplies then available. I wanted to use if as a portable “camping” radio or at home so a 120 VAC supply was in order. So I built one from junk-box parts, principally around a Triad R-50BC power transformer obtained at a swap meet. It provides all voltages for the transmitter and receiver including 500 VDC plate power and regulated 108 VDC, 6.3 VDC and 1.5 VDC for the Receiver HV and all filaments. The Ammo can was the obvious choice for packaging but there was a lot of stuff to go inside and there was little panel space available for the large GRC power connector. So I used a smaller multipin panel and matching cable connector, also swap-meet supplied. The result works well and runs fairly cool with the large perforated metal panel for ventilation. It can bee seen “in action” at other posts on this Blog. Handy field power supply. See below. Some field Ops with this power supply and the GRC-9. GRC-9 in the field

Then I needed a small, tactical SIGINT receiver utilizing a spectrum analyzer to drive an external oscilloscope for display of signal strength versus frequency. So I built up a circuit using a TV tuner front-end module which was electrically tunable from about 20 – 500 mc. The TV tuner front-end idea was loosely based upon a mid-1980’s Ham Radio magazine spectrum analyzer article. I built a fairly linear sawtooth generator to drive the tuner VCO and amplified and detected the “video” with a simple IC amplifier to drive the scope. It displays signal amplitude versus frequency on the scope and it is pretty sensitive when used with an external discone antenna. It includes a squelch circuit and an internal VFO “marker” so I can place that on top of the signal of interest while feeding the VFO to an external frequency counter to nail the poor guy.

It has an internal speaker so I can also listen to selected voice comms and it is quite effective in detecting low-band VHF air search radars from interesting ships in the area. Hmmm, an Ammo box seems like the perfect packaging for this equipment. If anyone keys any kind of radio transmitter in the 20-500 MC band, I can instantly see it and then measure its frequency for “further action”. Pretty handy to use in conjunction with my COMMINT receiver above. I called it the “AN/ULQ-1A”. See below.

Below: set up with the oscilloscope display and frequency counter:

Homebrew SIGINT spectrum Analyser

Homebrew SIGINT spectrum Analyser

Here’s a close up of a typical display set to detect military transmitters in the 30-88 mc band.
DIY SIGINT Receiver display

DIY SIGINT Receiver display

The big cluster of signals on the right is about 30 FM broadcast stations, 88-108 mc. The smaller cluster on the left is the 13 meter shortwave broadcast band transmitters. The large “pip” about 3 cm from the left is the VFO marker signal, adjustable with the front panel knob and measured via the frequency counter. A couple of military or public safety transmitters in between the clusters. Very interesting to see what “pops up out of the noise”.
This receiver receives all signals within its limit settings, simultaneously. Nothing escapes notice inside the “low VHF” military band as scanned here! Fun with an old ammo box from 30 years ago; I built it in 1986.

Then I developed a need for a portable hydrophone amplifier to monitor interesting undersea activity in conjunction with harbor defense operations. This little device turned out to be pretty handy in its spiffy desert camo motiff. It uses a simple high gain IC amplifier and a switch to select any of 6 external hydrophones and then drive either headphones or an internal speaker.  It also powers the hydrophone preamplifiers.  Like the COMMINT receiver above, it is powered by an internal PRC-25/77 battery BA-386/4386 for a LONG time. Hmmm, a small 7.62 mm Ammo box would be perfect for this. With this equipment you can hear the proverbial “Fish Fart in Fiji”. See below.

Then, we come to the more mundane uses for Ammo boxes. Here a large box is utilized as a transport  and storage box for a complete RS-6 Radio Set, complete with antennas, headphones and all accessories. See the other Posts on this Blog regarding the RS-6 Radio Set: RS-6 Radio Set  Photo below.

Yet another Ammo Box radio system. Shown below is an FT-897 HF/VHF/UHF radio installed inside a larger (deeper) 60 mm Mortar ammo can.  Also inside the box are two 12 volt, 7 A-H gel cell batteries, an AC battery charger, a Vibroplex keyer paddle  and an antenna tuner. This setup is shown at at a mountaintop camp in the Sierra Nevada mountains during some cold weather training exercises with the Golden Gate Young Marines. They are a USMC-sponsored youth development group for teens emphasizing leadership development, teamwork and self-discipline . We were up in the Sierras for a 3 day snow camping trip and we were a long way from the nearest cellphone coverage area.

So along comes comms back to home base in case we needed it. The Young Marines also received instruction in radio communications towards a training ribbon and I think they got a good exposure to Ham Radio and field comms in the process.   We used it to contact “home” both on 2 meters FM via repeater and also on 75 meters SSB through our “Comms Support Unit”,  a buddy Ham back home.   Antennas were a 2 meter J-Pole hoisted into the tree on the left  and a quarter wave wire for 75 meters off to the right.  It was set up outside my hootch but I had to keep the batteries warm over night. (cold gel-cells inside a sleeping bag with you are a real treat!)  The 60 mm mortar Ammo Can: Consider the possibilities.

The basic mountain Comm Center.

Snow Camping Comms

Snow Camping Comms

Holding an orientation class with the kids on the Ammo Box Ham Radio system out in the mountains. Where none of your other gadgets actually work! We got radio checks on 75 meters from Hams all over California in the evening. Four or five of these kids went on to get their Ham licenses.