[Antennas] Q loaded versus unloaded

Wed, 1 Oct 2003 18:36:23 -0400

Dear Jim
> For resonance isn't there a formula that goes something like Q =Fr/Fbw Q
is
> equal to the frequency of resonance divided by bandwidth. In other words
> the narrow bandwidth is result of high Q.
>> Now since this applies to tuned circuits, could it also be applied to
> resonant antennas????? If so, then you can easily measure the Q of your
> resonant antenna.

An antenna, as seen at its feedpoint, is essentially a loaded, tuned
circuit. Whether it could be said to be best represented by a parallel tuned
circuit or a series tuned circuit is probably academic. One thing that is
certain is that the Q of the antenna (if it's really all that important)
would be a good indicator, not only of the bandwidth of the antenna, but
also an indicator of its efficiency. Generally speaking, an inordinately low
Q would very likely indicate a dummy load.
On the other hand, having built, tested and used antennas for at least 55
years, I find it odd that I have never, ever had to give any thought to the
Q of an antenna. There are so many other real concerns about antennas, that
I cannot get real excited about Q.
Bob Lay (W9DMK) in Dahlgren, VA
http://www.qsl.net/w9dmk