As practicality approaches zero, fun tends to infinity

I found what appears to be an M185 shop on an M35 (deuce and a half) truck. Seems to be in good shape automotively, and the lights and power distribution in the van all work well. Previous use was an operations truck for the Wyoming National Guard based on the stickers and small commercial phone directory I found inside.

Is a 2 1/2 ton truck too much for hauling around amateur radio gear? Yes, but it will be a blast. Once the radio shack is put together, I wont have to lug around batteries and equipment. The shop has ample space to even be a camper of sorts. I am finding that many people convert these shop trucks to be campers, but my goal will be to approximate a military communications shelter.

Looking forward to getting a basic setup and getting out to the field for Parks on the Air.

CISC-RT-000130 – The Cisco router must be configured to restrict traffic destined to itself.

Seeing no discussion on this, and no useable examples from any source, I thought I would share -a- way of doing this. This hasn’t stood scrutiny of inspectors, but it does what the Security Technical Implementation Guides (STIG) states:

“Review the external and internal Access Control List (ACL)s to verify that the router is configured to only allow specific management and control plane traffic from specific sources destined to itself.”

Which I read to mean that for each interface, there will be an ACL, and for traffic destined specifically to that interface, there should be filters. Doing this per interface is fairly unwieldy, so I am taking advantage of the Cisco object groups to make this less of a pain. Instead of a custom ACL per interface, I can make a widely reusable ACL and I only have to create the Object group unique per router.

To start, define the addresses assigned to the router:
#object-group network This_Router
#host x.x.x.x
#host (each address on your router)

This will contain host statements of each address on this particular router, you can use “show ip int br” to get this.

You will also need object groups for management networks, voice networks (if your router has a voice gateway that requires devices to talk directly to this router), scanning networks, and other sources that need to directly talk to the router. You also need an object group for your entire allocation for pass through traffic. From this, you can build a decently manageable ACL:

!
!
ip access-list extended STIG_RT000130
permit tcp object-group Management_Networks eq 179 object-group This_Router (routing)
permit tcp object-group Management_Networks eq 49 object-group This_Router (TACACS)
permit tcp object-group Management_Networks eq 22 object-group This_Router (SSH)
permit tcp object-group Management_Networks eq 1812 object-group This_Router (Radius)
permit tcp object-group Management_Networks eq 1813 object-group This_Router (Radius)
permit udp object-group Management_Networks eq 123 object-group This_Router (NTP)
permit udp object-group Management_Networks eq 161 object-group This_Router (SNMP)
permit tcp object-group Scanning_Servers object-group This_Router
permit udp object-group Scanning_Servers object-group This_Router
deny icmp any object-group This_Router fragments log-input (For STIG CISC-RT-000140)
permit icmp object-group Allocated_Networks any (Permits internal networks to ping gateways)
deny icmp any any log-input
deny ip any object-group This_Router log-input (this is where you deny anything not explicitly permitted fulfilling the STIG RT000130 requirement)
permit ip any object-group Allocated_Networks (permit flow through traffic)
permit ip object-group Allocated_Networks any (permit flow through traffic)
permit udp host 0.0.0.0 eq 68 host 255.255.255.255 eq 67 (permit DHCP requests to pass through)
deny ip any any log-input (STIG requires that all ACL conclude with this)
!
!

To test this you can put a “permit ip any object-group This_Router log-input” right above the “deny ip any object-group This_Router log-input” statement to safely capture what is triggering that rule (using show log or wherever your logs go), evaluate if you need it, and add it to the ACL if so.

A real ACL will be larger than the example and will include rules specific to your environment. You will also have to stuff other STIGs in this (like STIG CISC-RT-000140 in the example) since you can only have one ACL per interface in a given direction (eg ‘in’ which this STIG requires “ip access-group STIG_RT000130 in”)

Don’t forget to remove the ACL from your interface(s) (particularly the one you manage through) before modifying the ACL or you could block yourself since an empty ACL would be deny any any. Best to do these things after hours and start a session with “reload in 60” without writing the configuration so if this does happen, you don’t interrupt people working and the router will go back to what it was before the ACL when the reload happens.

Springtime POTA, logging with typewritter

Remington Rand 5

The M37 isn’t done, but its been awhile since I have gone on a Parks on the Air trip so I loaded my pickup and the M101 and headed to Perry State Park, KS. In keeping with the Korean War era schtick, I brought a Remington typewriter and logged contracts with it. Not really efficient compared with using HAMRS or some logging program, but it worked and it was fun to do. In thinking about how my setup is coming together, it occurred to me that it is similar a RATT Rig (Radio Automatic Tele Type) in purpose, being an HF station at least. I remember the RATT rigs from the 80s/90s as a battalion long range communications setup (Bn <-> BDE), with FM/Wire serving the Bn <-> Battery/Company layer. We didn’t have tactical IP networks back then. I found a website, Rattrig.com, that shows an M37 setup which it pretty neat. I don’t think I will do the shelter part, but I think I can approximate a realistic role for an M37 as an HF station. People do use RTTY (the data transfer mode that RATT Rigs use) on the amateur bands so perhaps I can get a few contacts in that mode in upcoming POTA trips.

TA-312 Telephone set

TA-312 Telephone pair

I used the TA-312 a lot while on active duty, really quite a whole lot. At the time I really didn’t appreciate just how useful and rugged these phones are.

Using a TA-312 in the 90s

The US Army recently removed these from inventory (last decade or so), which I think was a mistake given what they can do. They provide reliable communications for an area and do not give an interceptable signal like radios do. They are compact, can take a beating, and are quite simple to understand. I found a pair of these recently and decided to pick them up. One of them had a ringer that wouldn’t ring, so I did have to do some repair.

Despite using these phones extensively, I don’t believe I have ever seen the inside. I took my time, consulted what info I could find on the internet (including Signal Center | U.S. Army Signal Corps field telephones and switchboards) and identified what I needed to fix the phone with a broken ringer. The ringer is part “Buzzer BZ-23/PT” and is held in place by the 4 external screws and a small pin connecting the ringer assembly to the ringer volume control knob. There are two wires that require solder connections as well and are color coded so it is clear what goes where. This job looked intimidating at first, but was actually quite straightforward with patience, lots of photos, and referencing the SignalCenter website.

I got handset spaghetti cables and other miscellaneous parts from SignalCenter.com and the ringer/buzzer from Fair Radio Sales – Electronic Military and Industrial Surplus.

Replacing the handset spaghetti cable took some patience, but also was fairly straightforward to do. I took lots of photos but the individual cables are color coded so it actually wasn’t hard to do at all. The spaghetti cable has a small hook on either end that prevents the cable from backing out when it is pulled on. Fishing the small cables through the handset and phone body was not as difficult as I expected.

Phone body internals
Some TA-312s have the schematic inside them

I don’t anticipate these phones being incredibly useful for amateur radio events, but they should be a very interesting addition as part of the overall setup I have when people visit the station in the field.

Thank you to Signal Center | U.S. Army Signal Corps field telephones and switchboards for the TA-312 information and parts and Fair Radio Sales – Electronic Military and Industrial Surplus for the “buzzer”.

H45 in M-1950 Hex tent

I rarely saw the H45 on active duty, and when I did it was in the GP Small or medium tents. I have an M1950 Yukon stove same as I used with the hex tent on active duty, but with liquid fuel (diesel/mogas). Burning wood in the Yukon does work, but it takes frequent fire maintenance and it is difficult to manage temperature output with it. I also found coal to be difficult to burn in the Yukon, it just really isn’t set up to do this. Coal would be nice as a compact and long burning fuel.

I have seen the H45 on sale quite often, so I ordered one. The stove itself wasn’t much, but shipping for the large crate was expensive. The solid fuel component I was unable to find for sale anywhere. I had one made and I am happy with it, even if it’s heavier than the original.

Solid fuel basket

My main worry was that the H45 would be too large and put out too much heat, but was pleasantly surprised to find that temperature control is much easier and even with the H45 vs Yukon. It is bigger than the Yukon, but in height and not really length so I don’t lose floorspace using it.

H45 test run

Using coal as a fuel works very well, with very long and even burn times, well beyond overnight without messing with it.

Coal fire

Ill keep the Yukon of course, it is more compact and easier to setup, but the H45 works well in an M1950 Hex tent and I expect ill use the H45 for most of my winter camping.

Adapting the HYF-370 horn to Ordnance Piece 7728341, MX-4003-UT

The original horn in the M37 matched its original electrical system, 24v. If you have a converted M37 there really isn’t a 12v horn that directly replaces a failed horn. On my truck, there is a modern 12v horn concealed that works out, but I wanted to use the original part if possible. The original horn was corroded in the interior, so this ruled out using a 12/24v converter. Vintage Power Wagons sells the 12v HYF-370 horn, which does fit in the MX-4003-UT housing with a bit of fitting.

Metal dowel holds the MX-4003-UT halves together

The screws holes holding the HYF-370 together need drilled out a little to fit, and the HYF-370 came with a gasket between the two halves so I used a small amount of permatex with the gasket to compensate for the slightly larger holes. The original horn housing is held together with a large hand turnable part (below) which the HYF-370 does not have a hole for, but it does have a bolt shaft in the center so a metal dowel works to hold the thing together. Shaping and tapping this was fairly straightforward, I used M8x1.25 and 10NF32 taps, but I am not sure how consistent this would be.

Backside of MX-4003-UT
Finished horn

I put terminals on the wires, soldered the other end to the douglas connector, hooked it up and it works. Sounds appropriately truck like, even if it likely does not sound exactly like an original.

If you have an M37 with 12v, and your horn isn’t working, this is one way to get this working and still look mostly correct.

PRC-9 Finishing Touches

ORG | CH Table painted and ST-120 A/PR harness

Found a manpack harness at Apex Gun Parts Gun Parts & Accessories (apexgunparts.com) who seem to have a wide selection of various parts. The WWII era belt was from Overlooked Surplus in Leavenworth, KS Overlooked Military Surplus (wwiigimilitarysurplus.com). Overlooked Surplus has a very interesting selection, and I will definitely be stopping by there more as the budget allows. They have an old field desk of particular interest to me.

The painting was done with stencils I made on a Cricut machine, which did ok but difficult to work with the tiny lettering needed. I got it, but it took a couple attempts. The ORG | CH table above the dataplate I assume was for operators to jot down frequencies of units they worked with. Small space to write, however, no idea how practical this was in the field. The other marking was “Pointer Adjust” and the nearby dial does move the frequency dial needle. I assume they found a known stable frequency and adjusted the needle to match that. These radios were continuously tuned, as opposed to later PRC-25/77s or modern SINCGARS where turning the tuning dial stepped a set amount of kilohertz.

Pointer Adjust label

Pretty happy with the final result and it is now ready to go in the truck when it gets back from service. I still have to work out the antenna and mount, since the installed antenna wont work well with 2m radio and the flex antenna stuck on the radio isn’t hooked to anything – it also is tuned for MIL frequency range. The flex antenna does look nice though. For the vehicle antenna, which will connect to the BNC Aux antenna connector, I am looking at a Firestick 2m type which should look similar or at least not too out of place. It comes in black and the conductor is spiraled over the fiberglass whip, but hopefully is fine after paint.

Good, Cheap, Fast – Pick One

Normally this is pick two, but for old military vehicles, it seems to be pick one (and probably best to pick ‘good’). I have been fortunate to find people that are familiar with this era of machine and find this project interesting. I don’t think the truck will be ready for Winter Field Day 2023, but it is getting closer.

M37 with rebuilt engine newly installed

I bought the engine hand crank as an accessory, while attempting to start the engine with that is very risky, it is good for turning the engine for timing and such. I am glad I got it for this purpose. The radiator has an access port for this so even with the engine completely assembled for operation, this crank can be used. The crank itself wasn’t very expensive, I think under $100 or so from Vintage Power Wagons.

Looking forward to getting the truck back and on the road.

Habits I had as an S6

The Army Signal basic course is generally designed for a track beginning in signal units. Some new lieutenants may find themselves assigned as an S6 in some other type of unit and there isn’t much opportunity to figure things out before finding themselves having to know things that really weren’t covered in training. Here are the habits I developed to ensure that me, my section, and my unit were prepared to communicate effectively.

  1. Find out what the unit is supposed to have
  2. Find out what the unit actually has
  3. Find out what the maintenance status of this stuff is
  4. Find out how the unit operates by doctrine and how communications are part of this
  5. Find out how the unit actually uses the equipment in operations
  6. Find the TMs, and any locally made documentation for systems
  7. Find out the capabilities of the equipment your unit is assigned
  8. Find out if there is any training time available that you can request for these systems
  9. Find out the training events of the unit and start planning for these 12-24 months out

Finding out what the unit is supposed to have should be fairly straightforward. Your S4 or supply Seargent should have access to print the Modified Table of Equipment (MTOE). The MTOE is the allocation of people and equipment for your unit and will list almost everything. Analyze this and extract communications equipment and to what section it belongs to. I found it useful to make a slide deck of sections and the equipment they have, with photographs of the equipment. Section leads stated they found this reference helpful when doing inventories particularly with little used equipment. This reference will have value for you so that you know exactly where equipment is supposed to go and who is responsible for it.

The unit may have communications equipment that are additional authorized items, or they have issued for some special purpose. Accounting for these and including them in your inventories will give you a complete picture of what the unit has (or should have). Some items are authorized for purchase based on unit priorities, such as power supplies for dismounted radios or special antennas, looking into these and seeing what is available would be a good use of time. One vendor is PTS Inc – Tactical Expeditionary Communications | Huntsville, AL | PTS, Inc. (pts-inc.com) which carries useful accessory items that the unit may want to buy. Your S4 will tell you the feasibility of this. In some cases, you may have equipment that is on your MTOE that has not been issued for a variety of reasons. Knowing what special non-MTOE items you have and what MTOE items you are short gives you the whole picture.

Finding the maintenance status is tougher to get a handle on. Your S4 can get you on the right track, but it will take some doing. Your supply Seargent can help you with the HQ unit, but the companies/batteries will have to provide info on their units. You won’t have tasking authority as the S6, but you can think through what information you need, think through what is realistic for an already busy unit to accomplish, and task units via your S3 (who does have tasking authority) to provide that information. Most communications equipment have periodic maintenance that needs to be deliberately managed, talk with your support facility to find out what needs this and how often. Having your equipment stuck in periodic maintenance when it is needed for training is a very bad situation. Look at your training calendar for 12-24 months out and request deliberate operator maintenance events and identify periodic maintenance opportunities so this is never a surprise to anyone.

Knowing your unit and its doctrine is very important. You cannot provide effective communications plans if you are unfamiliar with what your unit does on the battlefield and the terminology they use in operations. Ask your S3 to point you to the doctrinal publications for your unit – for example (cannon) artillery would be The Field Artillery Cannon Battery ATP 3-09.50 and The Field Artillery Cannon Battalion ATP 3-09.23.

Doctrine and what a unit actually does may be different to varying degrees. Participate in Military Decision Making Process (MDMP) meetings to fully understand operations even if communications does not come up directly. Knowing, in detail, an operation will give you insight how to best support with communications. You will be at a disadvantage if you opt to limit your participation. Ask questions at an appropriate time about items you aren’t following. Details about how the unit historically distributes communications security keys, how they establish communications nets, who is required to participate in what net, and similar items will help you to plan for these critical items, or if possible, improve these processes. Involve your NCOs and your S3 if you wish to modify something.

Finding TMs for equipment you have should be straightforward, if you don’t have them order them though your publications rep, or some are available on Army Publishing Directorate (APD) – https://armypubs.army.mil/. Prioritize your reading based on how important the system is in operations but read these TMs. You will have to understand the capabilities of the equipment if you are to make effective communications plans. The TMs likely will reveal little known capabilities that you can incorporate in your plans after you test them. Some systems are complex and TMs are inadequate to explain startup/shutdown and common tasks. In particular, information systems require this sort of locally made reference set. If they don’t exist, ask for them to be created. I would test these common task procedures by doing the task myself, if I could do the task, the documentation was acceptable. Having one or two soldiers that know everything and consequently are stressed when operations are in progress is undesirable, take note of things that consume their time and are easily made into a procedure document and spread the workload. IT people can sometimes be protective of their systems so you may have to insist, but the payoff will be your experienced soldiers can focus on advanced problems and newer soldiers can work on the routine tasks.

The TMs will introduce you to the capabilities of your equipment, but without testing, it is risky to offer a capability to the staff for an operation. Signal soldiers tend to enjoy testing new features so making a realistic testing plan and criteria for success is usually a fun challenge for them. Once you verify that a feature is reliable in a variety of conditions, you can offer these capabilities to the staff as options for an operation. Shorthand capabilities or ‘Planning Range’ (for radios) is a good way to express things to non-signal soldiers but exercise these things as experiments. For example, conducting a terrain analysis for an area then sending a team to verify a radio set works where you expect it too, and fails where you think it may can be a useful experiment as well as interesting training for soldiers.

Look at your training calendar for opportunities to train the soldiers in your section primarily, and for opportunities to provide systems training to your unit in general. Your soldiers will generally enjoy unique training experiences that aren’t difficult to pull off. One example I was able to do was to send soldiers to a state park and set up an HF station so we could test some PRC-150 capabilities. This kind of thing is difficult to do ad hoc, but much easier if you get it formally scheduled. The HHB/HHC Commander is the starting point for these kinds of things, particularly if you want to involve the Battery/Company as a whole such as for training of loading radios or operator maintenance. Asking your Commo chief to make (or have made) some realistic class outlines and slides for various subjects that your section can present is useful and generally welcome for inclusion on the units training calendar.

Planning 12-24 months out gives you ample time to gather needed items for training events. Executing a good communications plan really takes some extensive groundwork to make work, you have to consider the large number of items from the antenna to the handmike. Comsec, batteries, cables, accessories, Annex H to the OPORD (and all of it’s contents), spares, and much more all have to be considered before an operation. Generally, during an operation is too late to get something, particularly if you go to a distant training area and going to home station is not feasible. I made a checklist for myself and insisted that my Commo chief had one as well of all the tasks and items we needed for an operation. If we found something missing, we added it to our checklists. Knowing what you will be expected to do well in advance gives sufficient time to order shortages, do maintenance on the critical items, and think through your plans in detail.

Knowing what equipment you have, what it can do, what its status is, and having a well thought out plan of how to use it will answer nearly all questions your Commander may have for you. Most non-signal people like straightforward, non technical, answers to questions so anticipate questions that you may be asked and how to answer these questions without diving into deep technical explanations. Having answers to the above items will increase your confidence and increase the confidence your Commander and staff will have in you.

Over the last 20 years the US Army has been fighting a counterinsurgency. Communications requirements for this is quite different than what the US Army may be facing in the future. Having been around since the 80s (Cold War era), I remember communications that favored mobility and rather complex communications security (eg SOIs with changing identifiers, frequently changing frequencies, etc). IT systems are most definitely not mobile, and while you will have to maintain and train with these items, do advocate for training with mobile systems like FM and HF from time to time. Try to anticipate how a unit might fight in a future conflict, and how you can adapt what you have to these environments. Anticipate what your potential enemies might do to disrupt your communications and what you could do in response.

Completed Project – Modern 2m Amateur Radio inside 1950’s AN/PRC-9

Completed Set
From This

The M37 Truck came with a radio antenna, and I thought it would be nice to be able to use that. My overall goal was to make use of the equipment that came with the truck (antenna mount and LS-166 speaker), have a useable method of communication while in the truck, and have the radio appear to be ‘period correct’ (meaning the equipment would look like it would be in use in the 1950’s era). I didn’t want to ruin restorable equipment while doing this.

The actual antenna mount is an AB-15 base on AB-243 mount with antenna elements, but these are tuned for 30-90MHz, not 144-148MHz used by the 2m amateur radio I prefer to use. It is possible to use a working AN/PRC-8/9/10 on amateur radio (on 6m) but there isn’t a lot of activity there that I have found, although solar activity dictates this in cycles of which we are in a bad period. I also could have used CB but having monitored that over the last couple years in my area, I have not found anything interesting on it. That leaves 2m, which in my area is active and interesting to use. I also had an Icom 880H radio that hasn’t seen much use since I sold the car that it was in previously. Having the 880H as the working radio, I just needed the shell, and the AN/PRC-8/9/10 series of radios had it all – it looks great, is of the correct time period, and is large enough to contain the 880H.

Fair Radio SalesFair Radio Sales – Electronic Military and Industrial SurplusProvided the AN/PRC-9 and hand mike
AB5NHM-133 | ab5n-mic-upgrades (7000mic.com)Provided components and assistance
Tiny MicrosIcom HM-98/HM-133 Internals – Wiki (tinymicros.com)Specifics on the HM-133 (Icom) hand mike
N6CCPRC-10 Infantry Radio | N6CCInformation on the PRC-8/9/10 series
K4CHEPRC-10 Info Section 1 (k4che.com)Information on the PRC-8/9/10 series – Details on restoring an original set
PRC68.comH-33 Handset (prc68.com)Details on the H-33 hand mike
Vendor and Resource List
PRC-9
PRC-9
Icom 880H padding and wiring in battery box
Icom HM-133 circuit board, 12v to 3v buck, and photo isolating switch for PTT

Painting may not be needed depending on the condition of the set, but the example I had needed it. The paint must be thin to look correct. Painting of the raised letters worked with a stiff rubber applicator while painting upside down to discourage paint wicking. Paint that flows outside of where it is supposed to go can be gently removed with magnifier, an exacto, and patience after it dries. I used POR-15 as primer since I had some for another project, but it appears to adhere quite tenaciously and should be a good choice, as long as it is applied thinly.

For the electronics, I couldn’t escape using the Icom HM-133 hand mike circuit board since it uses bitstreams to code PTT on and off. The PTT trigger is very sensitive and would key up when connecting any kind of mechanical switch which is why I used a photo isolating switch for it. The HM-133 required de soldering of the PTT switch and the microphone element. I soldered wire leads from those holes to their destinations and there is little room to work with, but it worked. The HM-133 is in a block of foam cut to keep it in place with a plastic cover on it to prevent shorting. Schematics in the previous post.

I was able to preserve the function of the original on/off rotary switch as an on/off switch for the PTT and display LEDs, but the Icom 880H control head still powers the 880H on/off. The volume and squelch of the original I could not find a straightforward method of adapting these, but it might be possible later. The tuning knob and display of the original still works visually but had no effect on the radio operation. It does look nice cleaned up and illuminated, however.

Internal wiring is a balancing act of having enough to disassemble, but not so much as to no longer fit. I oriented it with the 880H fan facing the rear so hot air could leave via a vent hole I cut in the PRC-9 battery box. It would have been more convenient for wiring if it was the other way, but it would have no place to vent. This vent and the hole for external speaker, power, and 880H control head line is concealed by the (very handy) swing out feet on the battery box.

When I get the truck back ill find a way to mount it in there but finding references on installing radios in the M37 are scarce. I find some reference to mounting in the truck bed, but I’ll try to adapt something to the cab.