Electronic – How to calculate telescopic antenna impedance

antennaimpedancetransmitter

enter image description hereI'm designing a 27 MHz transmitter for controling RC toy using TX-2B and RX-2B ICs. Thre is my output stage schematic (see attachment). Output impedance 50 Ohm. I know that antenna length on 27 Mhz should be l (wave length)/4 = 2,77 m (quarter wave antenna) and impedance of that antenna is approximately 36 Ohm. But its too long antenna. I want to use small chineese telescopic antenna (97 cm) . Antenna lenth can be reduced connecting serires inductor. According to this https://m0ukd.com/calculators/loaded-quarter-wave-antenna-inductance-calculator/ in my case loading inductance should be 5.12 uH. Now our antenna reactance is zero: $$Im(Z_{a})=0$$How about antenna resistance $$R = R_{Radiation} + R_{Loss}$$ How i can calculate it?

Best Answer

Radiation resistance versus monopole height: -

enter image description here
(source: strobbe.eu)

Your monopole is about 0.088 of \$\lambda\$ so radiation resistance will be about 3 ohms. Here's the formula: -

enter image description here

Stuff taken from this website.

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