Hello,

What does "Q" actually stand for as i can't find anyone that can explain
this. I know many people repeat paragraphs of books without understanding
them!
Are you stating "Q" is reactance divided by resistance or "Q" = reactance OR
resistance. You obviously know what you mean but it isn't too clear the way
you're explaining it.

What is "Q" ? So far on this group I have had many answers such as it means
"quality" "goodness" "resitance" etc, but no one can give a similar answer
to anyone else. Does anyone really know or is it a made up term.


"Reg Edwards" wrote in message
...
Knowledge of antenna bandwidth is not of great practical use at HF
because
the Q of the feedline plus tuner has at least the same effect on the
overall
system bandwidth as the antenna.

I'm sorry, you lost me there Reg. How does the Q of a modern
broadband amplifier feeding a nom. 75 ohm feedline contribute more to
system Q than an 80 meter 1/2 wave dipole made from 2mm wire -- or for
that matter even one that's a half-meter diameter cage (though by then
it doesn't much matter for ham use)?

Cheers,
Tom
================================
Tom, who said anything about 75-ohm lines? And there's still a tuner,
with
FIXED settings, to contend with.

In any case an antenna can present a match to a line at only one frequency
in the band. The transmission line transforms the mismatch at the antenna
to something else at the tuner and something yet again at the transmitter.

Lines and tuners have lots of inductive reactance, lots of capacitative
reactance, but not a lot of resistance. Which are just as much a part of
the system as the antenna, if not the greater part. Q =
reactance/resistance. Bandwidth is proportional to 1/Q

What the transmitter sees, even with a precisely known antenna bandwidth,
is
anybody's guess.
----
Reg, G4FGQ

"AM200" wrote in message ...

What does "Q" actually stand for as i can't find anyone that can explain
this.

Q is generally taken to "stand for" quality factor. The definition I
like to go back to when all else fails is "energy stored divided by
energy dissipated per radian." Q really only makes sense when you are
talking about single resonators. This definition of Q applies to LC
tanks, coaxial cavities, hollow cavities, acoustic resonators,
pendulums, or any other singly resonant structure.

High Q resonators "ring" for a long time, a lot of cycles. Low Q
resonators dissipate energy rapidly and the ringing fades quickly.

Cheers,
Tom