Several months ago, I set out to build a radio system with a few requirements, and quickly ended up falling head first down the radio nerd rabbit hole. A seemingly simple task turned into scope creep, but ended up with a very flexible and capable manpack radio system.
To start with, what I wanted was:
A highly portable 'base station' in a backpack. I wasn't after a super lightweight system I would be humping for miles through the woods. I was willing to absorb some weight intending this to be primarily truck deployed. But, above all, I wanted base station power untethered to a vehicle or a home.
I wanted flexibility in power options, and in deployment. If I had the time to set up a big boy antenna/mast system, I wanted to have that available. If I didn't I wanted to be able to stab a short antenna into the radio and get to work. I wanted battery power, in addition to the ability to harvest power from multiple other sources. I did not want to be stuck with 15 pounds of junk because plan A and B both failed.
I wanted a system that could act in either simplex (radio to radio), could contact repeaters, and even act as a repeater in a pinch to extend the range of any handhelds in the area.
Yes, I like a challenge, and I wanted to be able to pull all of this off for a complexity level and price tag normal(ish) people can stomach.
The Base Radio
Having already committed to GMRS as my radio band of choice, and wanting the capability to throw the maximum allowed power of 50 watts into the air if needed, my choices for a radio to base this system around were limited. BTech had released their GMRS50-V2 recently, Midland had the MXT500, and Wouxun had just updated their KG-1000G to the plus version. The difference in price was not inconsequential, but in the end the Wouxun won me over. Build quality and features seemed to justify the additional price, and the radio being a superheterodyne design ended up being a VERY important consideration for all of my goals.
To add some protection and configure this radio as would be required for backpacking it, I grabbed a set of packframes from Armoloq made for this radio. The Armoloq frames are burly, reasonably priced, and include relocation mounts to move the antenna connection towards the faceplate (they also offer audio jack relocation, which I have purchased but have yet to install.) Powering this contraption is a Nermak 20ah battery from Amazon, a decision that ended up giving me some heartburn when it came time for testing. Battery charging is handled with an Ultrapower LiFePO4 battery charger, able to charge at 4 ah and making relatively quick work of recharging the battery. I also purchased or made leads to direct connect to a battery, or grab power from a cigarette lighter port in a vehicle (with the understanding that transmitting power level must be lowered in those cases). All of these wiring connections between battery/charger/radio/etc. all rely on Anderson connectors for the sake of universality, and all connections are fused as close to the battery positive as humanly possible. I'll clock some bonus points for having spare fuses on board the pack, just in case.
The Antenna
Courtesy of the Armoloq shopping trip, my formerly SO239 antenna connection on the back of the radio was now relocated and converted to BNC. For those quick, short range, stand up in a hurry type of movements I grabbed a pair of HYS GMRS 15" antennas from Amazon. These have proven sufficient for short range comms, maybe out to a couple miles, but will not hold a candle to a taller antenna with more gain. To that end, I grabbed a GMRS Slim Jim antenna from N9TAX. Being a roll up slim jim type antenna, it easily stows in my pack and comes with sixteen feet of coax ready to run if I decide to toss a rope into a tree and hoist it up. If no tree presents itself, the Spiderbeam 12m fiberglass mast has demonstrated itself easily capable of supporting this lightweight antenna at heights sufficient to easily clear houses and small trees. With the latter antenna option, I have been able to reach repeaters close to 30 miles away, demonstrating a sizeable range advantage over the shorter whip antenna and pushing the capabilities of some home base stations. All of this available from a 15 pound backpack and a four foot tube of fiberglass, running off battery power.
Making It A Repeater
Having accomplished much of what I set out to, a truly capable yet still portable base station in a backpack, I decided to tackle the last challenge: making all of this radio dork gear into a field deployable repeater. This was where the complications started stacking up, as typical duplex repeaters involve a second radio, a duplexer (which kills some output power), and would essentially double the weight and size of the entire setup I had already built, something that would move it well out of the realm of field deployable. What I was left with was the much derided and little loved world of Simplex Repeaters, in which a controller is hooked to a single radio which receives a transmission, stores it, keys up the same radio, and rebroadcasts it. This differs greatly from duplex repeaters which typically receive and broadcast on separate frequencies simultaneously. What the Duplex receiver grants is a freer flowing conversation and more ease of use than the simplex receiver, in which users must talk, listen to their own broadcast, then wait for the other party to talk, and rebroadcast. In practice, this makes every transmission take twice as long, and limits the ability of multiple people to use the repeater without tying it up. In my situation though, it was the only decision to make.
I looked at Argent Data Systems SR-1 Simplex Repeater, and haven't regretted my decision a bit since. A patron of the show (knowing rednecks in Texas with electronics experience comes in handy) gave me some major assistance building the required patch cable to connect the SR-1 to the microphone port on the KG-1000G, and within a couple minutes the radio was singing back and forth to one of my handhelds. As a simplex repeater, is showed itself easily capable of parroting back and forth, as long as users understood we were tying up a simplex channel (1-7) and we were limited to 5 watts of power. Moving up to channels 15-22 would allow the manpack to operate at the full 50 watts of transmitting power, but still only in simplex. The downside is, anyone within listening distance of the originator of a message would hear that transmission, and the transmission coming back out of the repeater. I wanted a little more elegant solution.
The Wouxun KG-1000g being a superheterodyne radio paid off at exactly this time. Since it is in essence two radios in a single chassis, I did the following.
1. Activate "Dual Watch" mode, so the radio can listen to two separate frequencies at the same time. This also allowed it to listen on one frequency, but transmit on another.
2. Set Side B in frequency mode, set to 467.550 mhz. Turn the volume on this side (the Wouxun has separate volume knobs for each side) to about 25.
3. Set Side A in Channel Mode to GMRS-15 (462.550 mhz), and turn the volume to 0. Select Side A as the active side of the radio.
The net result of this is the radio now listens ONLY to 467.550 mhz (the repeater input frequency corresponding to Repeater 15 for GMRS), but transmits only on 462.550 mhz (repeater output frequency for the same.) This is the inverse of how a handheld or mobile GMRS station would operate Repeater channel 15, where they would broadcast on 467 and receive on 462. Now, with a bunch of scattered users, the originator of a transmission WILL still hear his transmission parroted back to him, but every other user will only hear the transmission one time. Any user in the area can jump on this repeater without use of CTSS or DCS tones, or without any specific knowledge other than the repeater frequency (which one could surmise just by scanning and listening). In the event of an emergency, or as I intend to operate this at Prepper Camp this year as a quick-deploy field repeater, it would be quick and easy to disseminate the repeater frequency to a wide group, and to dramatically expand the range of portable GMRS radios which are typically limited to about 3 miles. Just the rough LoS (line of sight) math says a forty foot antenna mast should be good for about an 8 mile operating radius, so a 16 MILE diameter reach.
I'm still doing some testing on this rig, putting it through its paces and working on small issues. The Nermak battery has proven tempermental about powering the radio at full 50 watts transmitting power, sometimes causing the BMS/battery management system to shut the battery down when we should be well within the rated amperage of the BMS. It has no such trouble at medium power, so up to 20 watts transmitting power isn't a problem. I would like to do some real world testing of this as a field repeater, see in practice how many people it really can support before people are stepping on each other so badly it's unusable. I also have a long term project to datalog the power usage of this radio, again in real world use, and see just how much time this 20ah battery has bought me. I may add some solar regeneration capabilities to the pack at a later time, though right now if I needed it I would simply plug in my Jackery and let it rip.
But at the end of the day I built what I set out to build. I wanted a base station in a bag, able to be deployed quickly from a bag or a truck. I wanted home base station power in a portable package. I wanted to be able to stand it up as a quick and dirty repeater to have local comms in the event of an extreme weather event. And I accomplished all of this for a small enough sum of cash I don't think my wife will smash my head with cast iron when she reads this. (Prices do not include tax or shipping, but were accurate as of publishing of this article)
Price List:
Wouxun KG-1000G $400
Nermak Battery $60
Ultrapower Battery Charger $30
HYS 15" whip antenna $20 for a pair
Spiderbeam 40' Mast $140
N9TAX antenna $35
Argent Data SR-1 $105 with upgraded memory
Miscellaneous wiring $120
Bag $Nothing (it was my daughter's diaper bag when she was little.)
Total $910
Phil Rabalais
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