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Field deplorable linked repeater network built on Allstar



Hello everyone,


I am a new GRMS licensee and this is my first post on this forum. So, it’s good to meet you all.

I have been a computer network engineer for 23 years, worked in video streaming and conferencing, telemedicine, backend systems of all types, and I am now venturing out in the mystical world of RF. I have had very limited experience with the RF side of 2.4 and 5GHz WiFi and 4GLTE systems, and have loved two-way since I was a kid, but now I have the budget to really get into it.

I have been researching how to link GMRS and stumbled onto this site and the grms.network videos.  Then I looked into what the amateur radios folks were doing with Allstar, EchoLink, and the like. I am pretty handy with a soldering iron, know enough to be dangerous with Linux, and understand the IP side of it very well. So, I thought I would try my hand at building a deployable linked repeater system.

What would be the use case, you say? Mostly because I am a geek and I think it would be cool. Beyond that, I can see it would be useful for events like marathons and adventure races, desert rally races, etc where someone was traveling in a linear distance and aid and comfort stations along the route needed to maintain comms. Distance in the desert, the ability to address terrain obstacles in adventure races in the mountains. That kind of thing. You could set up at night points along the route and blanket it with linked coverage. Or, that’s my idea for it anyway.

A lot of it is pretty straight forward, and I have really appreciated the information many have shared about GMRS linking. I have a good handle on the I{P requirements and how to use LTE to provide the private IP control and repeater interconnection network. But a couple of things have really hung me up. 

How to interface the radio hardware to the node computer. There are some great videos online about how to modify a BF-888s to create a hotspot node, and I can extrapolate the connection to radios that have a 14pin, 9DB, or 25DB control connections, But how can you get into other mobile radios at 50W that don’t have a control port in the back? I have bought a KG-1000g to play with and I think it’s built in repeater capability through a control cable to an identical radio would keep the system pretty compact. You would need a duplexer, but not a repeater controller? So, the question is how to wire in to what the URIx (ideally) or modded USB sound card needs? If it can be done on the BF-888s, then I think it’s a question worth asking.

The other thing is the Allstar server backend. Is it in the node package, or is that a separate package?

If I can get these two issues moving, I think I can make something cool.

At any rate, I will be around if anyone can use what I know. I am happy to tell you what I know and tell you if I don’t know.

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Good morning and welcome to GMRS and the MyGMRS group.

The main difference between the ham radio and GMRS linked groups (Aside from using different server groups to prevent unlicensed traffic in either direction) is that Mygmrs isn't quite set up for mobile linked repeaters. Many races currently use active ham radio groups or local emergency service radios for traffic relay. This is because these groups are set up for emergency remote radio operations and many times use VHF simplex to achieve their goals. in my years as an EDS operator, I can only think of one time where we set up a repeater, and that was because of a large forest fire in southern NJ where a NJFS tower was affected. Any other time, whether it be at an evac site, or during a race event, or even when we followed a group across the state for their march to DC, we always used VHF FM simplex for comms.

It could be useful for perhaps camping, where one group may wish to communicate back home to a base repeater, but thats really the only extent I can see a mobile linked GMRS repeater being used. Even then, there are other means of comms that could be used, such as Zello links, since lets face it, if your in a location without cell service, theres little to no chance your node would work either.

Now all that being said (and the boring stuff aside) The build you want is rather simple and the method I'll give is plug and play. You'll need 2 M1225 radios, flat pack duplexer, Rim-lite maxtrac repeater cable (note this is different from the standard rim-lite maxtrac cable as it should have two connectors), Pi and associated cables and parts, USB charger capable of 5+ amps continuous output, Slimjim antenna and coax, container to install everything in, and a really good battery to power everything for at least a couple days without recharge. You'll likely also need a mobile hotspot as well if you plan to be remote.

Start by programming the two M1225's. The TX radio should be set to low power (20W) This does three things, prevents de-sense in the duplexer, reduces the chances of burning out the finals on the radio due to extended transmit times, and extends battery life by reducing power draw. Once completed, attach your jumpers for the duplexer, and install the rim lite modules making sure not to reverse the connections. Attach the rim lite USB cable to the pi. wire in the radios, and the USB charger to the battery. Connect USB charger to the Pi, (This is how the Pi will get power to operate) Connect the RX/TX radio jumpers to the duplexer, attach coax to the duplexer and antenna to the coax.

Its a simple enough build with the only weak point being the battery as they are either overly expensive, or weigh so much that it makes the system much less portable. The battery I use for my portable repeater (Not linked) is meant for trolling motors on boats. It was about $250, and I was able to get about 2 days of use out of it before voltage dropped below 11VDC. The battery weighs about 25lbs.

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First off, thanks for the detailed reply.  The M1225 certainly seems to be the popular radio to use for linking projects. I want to use an in-production part 95 radio for the project if at all possible. My friends and I have KG-1000s mobiles in our trucks and we did that for reasons of commonality and group familiarization. It’s our Boeing 737 if we were an airline. When we are out together, if anyone has anything that breaks, or we need to swap/jump into someone else’s vehicle, we all know the radio and can use the comms just like they were ours. If anything breaks, we only need to carry one spare as a group. They are programmed the same from the same file ahead of the event. Besides, the interesting part to me is how to get the control interfaces working with current radio equipment. The repeater radios would also be identical, other than programming. Again, with the one spare for the group, I could send any of them out with a radio for a swap. So a big part of the appeal to me is figuring out what the control interface needs from the radio and figuring out how to mod the radio to provide it.  I could then, theoretically, apply that to any radio, at least in my head.

This is the no software, no problem support model I use in the enterprise IT world. Standardize on a platform, abstract everything you can, and don’t spend time troubleshooting an individual software problem. Just reimage it and move on. In the radio world, I imagine it as rip and replace the radio with a pre-programmed one and continue ops. Since I plan to make a few of these, standardization is critical to me. Sure, there are a lot of less expensive ways to do it, but my buddies live all over the country and time when we all get together is precious, So the real cost for me would be time spent fiddling with the comms network unnecessarily.

For LTE and WiFi connection, I am using the CradlePoint IBR series of routers.  I can manage then through a central cloud dashboard, update firmware, manage individual or group configurations, restart, or reconfigure them remotely with NetCloud Manager.  I know these systems very well. They are used in a lot of emergency vehicles for mobile data. I spec them for telemedicine units in ambulances. They also allow me to set up point to point directional WiFi links with yagi antennas, so connectivity outside of LTE coverage would not necessary be a problem as long as one of the repeaters was in a coverage area and could reach the others. They have the added benefit, when coupled with a repeater of extending WiFi access nearby the repeater for soft client use, configuration of the router or Pi, etc along the linked repeater path.

For power, I plan on using LiPO4 batteries from Dakota Lithium. Very pricy, but worth every penny in capacity, power to weight ratio, temperature tolerance, shock tolerance, and life cycle count. Coupled with foldable solar, I can keep the load up for quite a while with them. Managing the power, I will be using Victron chargers, shunts, DC-to-DC chargers that will buck boost and provide isolated and clean supply voltage, and report to Victron Remote Management (VRM) servers in the cloud (as long as my private IP network can route to the public internet) to allow remote control and management. I am very comfortable with these systems. I currently travel full time in my RV and have replaced it’s entire 120v and 12v power system with a 600AH Lithium system of my own design.

I really need to do some more digging on the Allstar server backend. My goal is not to link my routers with external nets, due to the temporary nature of field deployments and the mission-oriented support role they will play in our outings. So, I will need to replicate a stand-alone backend with whatever IP services I need to support the server. That is easy to do with virtualization and an infrastructure Pi.

At the end of the event, my buddies could just take home a repeater, plug it into their home networks and we could still talk together on our radios. They could take it to family events and have a reliable repeater there that I could remote manage the backend of, and I would learn a LOT about running a system like this. For all these uses, it’s worth it for me and my buddies.

End the end, I want to document everything and put it out to the community if anyone is interested in any component of it. I doubt many will want or need the whole thing, but parts of it could be very helpful to others, I imagine.

I know that this whole thing would be a lot easier to do as a Ham. I am studying for my ticket as I speak, but I want to build a fully legal, modern, and compliant way to do it for GMRS operators that don’t have a ticket, or are not interested in becoming Hams. Also know it would be MUCH easier to do with part 90 radios, but I really want the project to have legs long into the future, and a big part of that is how to get modern radios into the equation.

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Well, the 1225 is simply plug and play, no radio mods, no having to open the radio to soldier into different caps and pads to get the thing working. as I said, plug and play, and there are enough of them out there to make several repeaters and still have 5 or 6 radios as "spares"

The radios themselves will not be changed as often as your vehicle based radios or portables. Repeaters are restricted to 8 channel pairs, and once sent, typically can only use 1 pair without re-tuning the duplexer. For an event, (unless your doing something very long distance, like 30+ miles) 1 well placed repeater, either on a rooftop or on a portable 30' mast at the crest of a hill should get you at least 5-15 miles in each direction. Running multiple repeaters that close range would very quickly take up those 8 channels, and that doesn't include the risk of interfering with already existing equipment.


Not wanting interference from outside groups or persons added to all of that, well, it sounds like you would be better getting a national part 90 license which would allow you and any other people you wish to add to talk on a private channel. You could run digital or analog, encryption if thats your choice, even RAS to prevent unauthorized traffic from entering the system. Other users wouldn't need a GMRS or ham license, just give em a radio and go.

Another way to go would be network radio which only requires wifi or cell reception. This allows you to RoIP and you could in theory talk anywhere to anyone you set into your talkgroup. It would work just like the part 90 system, but without a license. Network radio is growing in popularity and will allow users to use both UHF and RoIP to talk long distances. The downside is I dont know that there are any current 90/95E compliant network radios.

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I didn’t mean private, as in restricted. I meant private as in the Allstar linking would only connect the deployed nodes and not to mygrms.com or grms.network. Not that i would have a problem with them linking to my repeaters, I just don’t think they would want to do to the temporary nature of their use case. Anyone in range could tune in and listen/chat about the event.  But, like I said, the most important aspect of it is that I think it would be cool to try out and establish the documentation for interfacing with new radios for future projects yet unknown. The old stock radios will run out eventually, ask anyone who collects surplus firearms. One day you can buy a crate of them for a c-note, but in a couple of years you’ll be hard pressed to find a serviceable example at several times the price. When demand eventually exceeds supply, you pay what you have to pay and are glad to get what you can get.

But, this isn’t an economics class and no defense of the expense of using new equipment could be taken seriously anyway. You are right, the plug and play way using type 90 radios is proven, cost-effective, and has already been done. As such,  it is a exercise in utility, not advancement of the base of knowledge. It is the “right” way to do it if you are doing it for utility, no argument here. It just doesn’t interest me in the same way as building something no one has ever seen before so that someone else can run with it from that point.

I really have to take my hat off to the grms.network gentleman for the innovation of using a modified BF-888s and a Pi as a simplex Allstar RF node. That is ingenuity.If I misattributing the accomplishment to him it is only out of ignorance on my part (and there is a lot to go where that came from ;).

At any rate, I appreciate you trying to talk me into my senses. I did learn a thing or two from your guidance and I appreciate the conversation.

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