[Prev][Next][Index][Thread]
Re: Q?
In a message dated 3/8/00 10:48:41 AM Central Standard Time, tesla-at-pupman-dot-com
writes:
<< Original Poster: "Raycroft" <k.raycroft-at-worldnet.att-dot-net>
>>>Hi all
I've heard a lot about "q", but don't really know what it is. Would
someone be kind enough to explain:
1. How to calculate
2. What it measures
3. What it is useful for
Thank you very much for your time,
Jason Raycroft<<<
Hi Jason,
Q is known as the Figure of Merit for an inductance coil. Q = X sub L over R
where
X sub L is the inductive reactance measured in Ohms. X sub L = 6.28 x fL
where f is the frequency in Hz and L is the inductance in Henries. R is the
DC resistance
also measured in Ohms. Therefore, Q is a dimensionless ratio. The efficiency
of
a coil increases with Q because with a low DC resistance the coil is able to
return
increasing amounts of energy to the circuit with the least amount of energy
lost to the DC resistance in the form of heat. A perfect coil has zero R and
infinite Q. As an inductance is tuned thru resonance, a high Q coil will have
a very sharp response
curve at the resonant frequency while a low Q coil will tune broadly.
Generally speaking, a high Q is desirable for a continuous wave coil. But in
the perverse nature of Tesla coils, a high Q is not always desirable for a
disruptive (spark gap) coil.
I would urge you to reference any of the classic radio engineering texts such
as Terman or Henney. There is also Circular 74 and the ARRL Handbook. John
Couture's Tesla Coil Design Manual is very good on how Q relates more
specifically to TC design.
I hope this helps and my explanation rates a reasonably good Figure of Merit.
:-))
Happy day,
Ralph Zekelman