Q-rating

[2DX727]

Two questions:



1. What is "Q" (I have an idea, but would like a specific definition)?



2. And, is it possible to calculate "Q" with a formula using the known physical measurements of an antenna, or is some sort of measuring device required (like finding the SWR)?


RCI-2950/GalaxyDX99V/TS667V/LMR-240/LiveWire Coil</p>

 

[Moleculo]

1. Q factor is a measure to describe the "Quality" of the circuit.



2. There are a couple different ways to measure Q factor. the ARRL Antenna book uses:



Center frequency X change in reactance for a given change in frequency / 2 X Resistance at the Center frequency X the change in frequency.



The other formula I've seen is:



Center Frequency / upper cutoff frequency - lower cutoff frequency. Cutoff Frequency is defined as the frequency at which the circuit output is reduced by -3db.



So I guess the answer is that it does take some precise measurements to determine the antenna Q factor. There are computer modeling programs that can figure it out for you based on physical dimensions.



MOleculo


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