Originally posted by peterhr
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(1) The impedance of half-wavelength dipole is 75 ohms, which gives full signal power transfer from antenna to receiver**.
(2) It's length does not depend on insulation's velocity factor. A fixed length of 69mm (center to tip) each limb for 1090 mhz, irrespective whether it is bare conductor or insulated with any insulation.
(3) It's impedance & gain is relatively insensitive to error in length. Hence if the limbs are not cut precisely to 69 mm, but say 67, or 68 or 70, or 71 mm, there will be no noticeable affect on it's performance.
It's only drawback is its low gain (2.2 dBi), which cannot handle long cable runs (mine is 50 feet). This problem I solved by adding a low cost satellite in line amplifier 950-2050Mhz, 13-20 dB.
Realizing these characteristics of half-wavelength dipole, it was the first antenna I decided to make, and after it's successful trial, posted it in FR24 'best antenna' forum.
My design was indoor type (see peterhr's very first post above, the second photo, one with a hand). This design is not useful for most hobbyists who use outdoor installation. It was very wise and thoughtful of peterhr to develop an outdoor design, which can be used by most hobbyists.
**When a 75 ohms antenna is connected to 75 ohm coax and 75 ohms usb receiver, the SWR = 1 (100% transfer of signal power from antenna to receiver). Even if 75 ohm antenna is used with 50 ohm coax and 50 ohm receiver, the SWR=1.5 (97% transfer of signal power from antenna to receiver), a very decent value
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