Thanks to Juliet-59 who sent this in after noticing this article, originally posted at The Survivalist Blog. What a GREAT partisan radio antenna project. If any of you come across useful comms articles like this, let us know! -JJS
photo credit: survivalistblog
This is a fun, almost novice-level construction project for anyone who has a 2-meter ham radio walkie talkie (e.g., the $26 BaoFeng UV5R) and would like more effective range without having to buy an amplifier. If you are currently using a short rubber-duckie antenna, this high-gain yagi antenna may well make your radio appear to have 6-10 times its power on 2 meters, doubling or tripling your range in relatively open areas, for a total cost about $21. [Dense high-rise central business city centers may not see as great an improvement, nor areas with impenetrable hills.] That may just make it possible for you to reach useful repeaters or friends from inside your house.
Using thick multi-ply packing/shipping corrugated cardboard to simplify construction (see the accompanying photo of the completed antenna), this antenna is for indoor or very protected outdoor usage only; it has to stay dry. This antenna can be “hung” like a large painting on any wall that “points” it in the right direction, as long as there isn’t a lot of metal in the wall, and the house doesn’t have metal siding (or buried rebars).
It can even be covered up with a large poster or a world map, and no one will even know it is there! This project can help teach newer users quite a bit about radio antennas. I came up with the idea after building several simple outdoor 2m/70cm yagi-style beam antennas (using a 1″x2″ wooden boom for support) and realized it could be adapted for indoor use. While my discussion is for the common vertical polarization (elements are aligned vertically) on 2 meters, it could also be set horizontally if your counterparty is using horizontal polarization.
It will also work on the 70cm band, but my results there are less satisfying.
This antenna was designed for center frequency of 146 MHz and 440 MHz. On 2 meters, this antenna will give you roughly 6dB gain over a full size dipole (6 “dBd”) , and probably 12 dB over the stubby “rubber duckie” antenna that probably accompanied your handheld transceiver. This is because electrically “very-short-for-wavelength” rubberduckie antennas have low “radiation resistance” and squander most of your transmitter’s power on 2 meters.  Building an antenna like this one is like multiplying your power by 4-10 times! If you have a favorite repeater, or a trusted ally you need to be able to reach, and a wall that “points” roughly in the correct direction (or even within 30 degrees of the correct direction) you’re in business.
2meter actual test results: Mathematical patterns based on theory are great, but real-world results are what count. I actually tested this antenna over a 1/4 mile range (>200 wavelengths, an excellent far field test). Using uncalibrated signal strength markings on a scanner radio set to the correct frequency (this is the best field strength equipment I currently own), and the same Baofeng transmitter on the same frequency on 2 meters, I sequentially tested: (1) the supplied rubber-duckie antenna, (2) a top-rated 15” whip antenna (Nagoya NA-771 15.6” dual band) , and (3) this homemade antenna, the results were 0 (zero) signal strength units for both rubber-duckie & Nagoya whip antenna, and 8 signal units with the antenna pointed frontwards, and 6 signal units turned 180 degrees (“backwards”). This suggests moderate front-to-back ratio and wonderful forward gain over a whip style antenna–a successful 2 meter high gain antenna..
70cm actual test results: Unfortunately my current results on 70 cm are not impressive. While the antenna also works on 70 cm, I can’t promise any significant gain there; it had the same signal strength as the whip & rubber duckie. On the 70 cm band, the whip/rubber duckie are a more significant fraction of a wavelength, and therefore perform better. Reception of a local repeater was somewhat better with the yagi than the other antennas, but again the difference was not impressive.. (Improvement may be tedious, but if I ever get it done, I’ll publish how to adjust for better 70cm performance.)
Preparation for Construction …
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