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.
Performance:
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. [1] 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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