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Impedance is the measure of the opposition that a circuit presents to an alternating current when a voltage is applied. This is a force of much interest to the radio amateur especially surrounding the connection to antennas.

1
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to RF ground, that is to say the grounded side of the coax connector. This works fine with no additional RF grounding. This and the well known fact that the impedance of a: 1/4-wave … vertical with good RF ground is ~35 Ohms. 1/2-wave dipole is ~70 Ohms. This matches very well with the GPIO impedance that is believed to be somewhere between 30-60 Ohms. (How to test?) Thus we can expect …
answered Mar 20 '17 by not2qubit
1
vote
2answers
we need impedance matching?) I would like to avoid any amplifiers or extra active hardware. EDIT-1: I'm of course fully aware of the legalities of TX on FM band. Apparently the RPi GPIO … impedance is around 30-60 Ohms. This is an antenna problem, because the question is equally valid for any transmitter. The best options I have seen so far is this FM loop or this quad loop... …
asked Mar 15 '17 by not2qubit
5
votes
2answers
I watched this video of a very nice explanation of a simple dipole and 1/4-wave monopole. In that video they show how you can impedance match the 1/4-wave monopole by bending the 4 (virtual ground … plane) pins downwards at an angle, $\theta$, from the horizontal plane. Doing this we can get any impedance ($Z$) between 25 and 70 $\Omega$. This is also very well explained here. However, on the …
asked Mar 10 '18 by not2qubit