There's a model of HT antenna for the GMRS band by Nagoya (NA-771G) that's specified as a half wave. How can that be? An end fed half wave antenna needs a 49:1 impedance transformer to match with the transmitter? Is it more like a 5/8 or 3/4 wave in reality?
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2 Answers
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Judging by looks, it's a half-wave element with an autotransformer at the base. Nagoya says the antenna is 15.3 inches in length. Taking measurements from a photo, the bottom 2 inches is in that fat molded section that clearly contains some kind of coil (the autotransformer), and the remainder is a whip that's around 13" long, which is perfect to be a half-wave at ~460 MHz.
This kind of design is seen reasonably often in handheld and mobile antennas.
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3$\begingroup$ I have a half wave telescoping 2m antenna. Big fat coil at the bottom. And a great way to break your SMA off if you're not careful. $\endgroup$ Feb 16 at 23:46
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It is worth noting that a vertical end-fed antenna is often used in conjunction with a ground plane that interacts strongly with the antenna to reduce its effective impedance to a value that the transmitter can drive directly, without any loading coil.
So, for example, the four drooping radials surrounding the vertical 1/4 wave "whip" of a 2-meter base station antenna let it match up well with a 52-ohm transmission line.
