Build Your Own Packable Field Antenna
If you’re looking for a capable antenna that’s lightweight, portable, and is rated for more than 100W, then this is the blog post for you.
These plans are offered for free to the community, but if you plan to build your own, please consider using the Amazon link here to purchase the components. A small 1% of the sale goes to supporting this site.
Scroll to the bottom of the page for a full parts list with links.
I built the packable field antenna a few months ago to take to the Western States 100 Ultramarathon. I was working with a team of other radio operators to relay information through the Sierra Nevada mountains at different stations as part of race operations. You can see a video of the Radio Go Box and the antenna being used to call in the race times of the ten race leaders on YouTube here.
The antenna I used is a Comet CA-2X4SRNMO (VHF and UHF 140-160 MHz / 435-465 MHz). It was chosen based on its moderate size and reputation for being a strong performer. It has decent gain (3.8db and 6.2db) and parts of the antenna element can be disassembled using an Allen wrench (if you really need to break it down for flying). It comes pretuned, but you can fine tune the antenna by adjusting it with the Allen wrench. In my experiments, the adjustments didn’t make any meaningful difference. The antenna can take up to 150 watts, far more than the 19 or so actual watts coming from the Radio Go Box.
The Aganz Radio Go Box pictured alongside the packable field antenna
The manufacturer claims VSWR of 1.5 : 1 or less, but mine ranged from 1.17 on GMRS frequencies, to 1.27 at 445mhz, and 1.55 at 145mhz. If you have questions about what SWR is and why it’s important, check out the FAQ here. As a rule of thumb, 1.5 is the highest most people like to go, after that you are going to experience some slight signal loss. I did experiment briefly with rolling out a counterpoise to try and ground the radio a little more at 440mhz, but at the end of the day a tripod antenna setup that’s not connected firmly to the frame of a car or attached to the roof of your house is going to have some limitations. I eventually just accepted it was going to be a little high on the 70Cm band.
A Nano VNA analyzer indicating SWR of the antenna along the frequency spectrum.
The MFJ-269 antenna analyzer used to confirm SWR on multiple bands.
The antenna connects to the mounting plate using a CK-3NMO connector (note that this plate is slightly different than the one pictured). NMO is a common mounting option for vehicles. It’s waterproof and very sturdy. It also means the antenna can be easily threaded and unthreaded off the mounting plate if need be. The O-ring in the NMO plug allows you keep the antenna outside of your tent even in the rain (just don’t operate your radio when lightning is present).
The tripod is an AOKA 15.7” Carbon Fiber mini tripod. The tripod was the hardest part to source when designing this antenna setup. I wanted something very strong but extremely minimalist. It had to have a wide enough base to support the 40” antenna, but it had to collapse down to fit into an extremely narrow area in a hiking pack. I removed the ball head, attached the supplied extension in the box, and used the Arca-style mounting plate that came with it to attach the mounting plate to the tripod using quick-detach. You’ll need a 1/4'“-20 nut to attach the mounting plate to the quick-detach plate.
The tripod arrives black with purple accents, so I immediately gave mine a rattle can paint job. I like to paint a lot of my field gear to blend in a little. It just looks cooler. Make sure to use non-metallic spray paint if you ever paint an antenna. Painting gear is easy (see this little tutorial), just take your time. Less is more. Netting and bursts of black make a big difference.
The field antenna collapsed and tucked into the exterior pocket of a Mystery Ranch Pop Up 38 pack.
Here’s the full parts list you’ll need to build your own:
Comet CA-2X4SRNMO Antenna (This is the NMO version, the non-NMO will not mount directly to hookup)
Comet CK-3NMO NMO Hookup with 16.75 ft. RG-188 and a PL-259 connection
One 1/4”-20 Nut
Some spray paint. The Walmart camo stuff is good.
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