Just an afterthought.

Q is dimensionless quantity. Therefore it cannot be measured directly.

It is always obtained as the CALCULATED ratio of TWO independent
measurements or previous calculations.

Its only use is to predict, by further calculation, other properties
of a circuit such as bandwith or voltage magnification. It is just a
convenient intermediary which can frequently be bypassed or done
without.

It can seldom be determined accurately which is a measure of its true
worth. Your guess is as good as mine at high frequencies.

The common or garden Q meter indicates only the resistance of a coil
relative to a standard of some sort. The coil's inductive reactance
is already known, or is related to the capacitor and frequency, or can
otherwise be calculated. Here you still have a pair of independent
measurable quantities.

I'd better stop here. The subject has been over-complicated quite
enough. Here in the Black Country, the weather is beautifully fresh.
Spring is well on its way.
----
Reg.

That (your afterthought) is much more like it. Thanks.

After all, this is NOT a thread about Q, it's a thread about the
effectiveness of different two-terminal devices for use in inductively
loading a linear radiator. In that case, the measured impedance, that
is, the measured X and R, of the two-terminal device is indeed what
matters. Given that we need a particular X, a high ratio of measured X
to measured R is advantageous, since the R term represents
dissipation. Maybe we should invent a new term and define it thus:

Xiddle = X(measured)/R(measured)

where Xiddle is to be pronounced "Ziddle," and rhymes with "piddle."
Or, we could just use the shorthand that W8JI elected to use AND DEFINE
in his posting: Q=X(meas)/R(meas).

Just as you say, Q is only an intermediate on the path to something
more interesting. It works for me if someone wants to offer a slightly
non-standard definition, so long as the definition is clear, as it was
to me from W8JI's post.

Thanks for mentioning the Black Country. It was an education for me to
look it up. Spring is trying to gain a toehold here, but it's a bit
tenuous. Got up to a couple feet of new snow in the hills over the
weekend.

Cheers,
Tom

(PS--where do you find gardens that grow "Q meters"? Or are they the
things that invade the garden to try to eat the qms?)

now that you guys have had fun with Q... how about trying the practical
aspects of the originally stated problem? how would the described element
loading compare with, lets say, a 40-2cd element? bandwidth? coupling
between yagi elements?? losses?

"K7ITM" wrote in message
oups.com...
That (your afterthought) is much more like it. Thanks.

After all, this is NOT a thread about Q, it's a thread about the
effectiveness of different two-terminal devices for use in inductively
loading a linear radiator. In that case, the measured impedance, that
is, the measured X and R, of the two-terminal device is indeed what
matters. Given that we need a particular X, a high ratio of measured X
to measured R is advantageous, since the R term represents
dissipation. Maybe we should invent a new term and define it thus:

Xiddle = X(measured)/R(measured)

where Xiddle is to be pronounced "Ziddle," and rhymes with "piddle."
Or, we could just use the shorthand that W8JI elected to use AND DEFINE
in his posting: Q=X(meas)/R(meas).

Just as you say, Q is only an intermediate on the path to something
more interesting. It works for me if someone wants to offer a slightly
non-standard definition, so long as the definition is clear, as it was
to me from W8JI's post.

Thanks for mentioning the Black Country. It was an education for me to
look it up. Spring is trying to gain a toehold here, but it's a bit
tenuous. Got up to a couple feet of new snow in the hills over the
weekend.

Cheers,
Tom

(PS--where do you find gardens that grow "Q meters"? Or are they the
things that invade the garden to try to eat the qms?)

On Mon, 17 Apr 2006 21:07:41 -0000, "Dave" wrote:

how would the described element loading compare

Hi Dave,

Without some expression of what you might find acceptable, or
unacceptable, comparisons are condemned to vagueness, or extreme
elaboration.

with, lets say, a 40-2cd element?

Approx. the same;

bandwidth?

Approx. the same;

coupling between yagi elements??

Greater, forcing a different geometry.

losses?

Approx. the same.

There is nothing in your question that breaks new ground, and
substituting equivalent components really only shuffles a few design
parameters. Such shuffling may entail considerable tedium in
implementation details, but you say nothing of what passes for good or
bad. We could equally rend the correspondence bandwidth here into the
equivalent tedium of quoting the partial dB differences - that has
been good for more than a thousand posts so far.

One of our infrequent correspondents here would substitute metal
tubing for bamboo wrapped with metalized mylar film. He couldn't
expect any gain in this swap, nor could we point out any considerable
loss; but let's face it, the market is not rushing to build antennas
this way because there is no economic nor technical justification.

Thus, the only advantage is one of marketing. If you cannot quote a
gain advantage, you can at least argue conservation because you are
doing Green DXing with Bamboo elements and recycled weather balloons.

So it comes down to a familiar question: What's your point?

73's
Richard Clark, KB7QHC

Just a second afterthought.

The measured impedance of a 2-terminal device tells you next to
nothing about it. It certainly does not tell you the Q.

To find anything useful about it, it is necessary to shift frequency
and make a SECOND measurement.

So we return, yet again, to a pair of independent measurements or
calculations in order to obtain a ratio.

A ratio has two degrees of freedom. I just love that phrase. I/ve been
waiting for years just to mention it.
----
Reg.

:-)

How nice it is to have modern instruments which cover a wide range of
frequencies in one simple measurement setup, display the results in any
of an array of formats, and even store the measurement results for use
in a variety of analysis programs.

(Sometimes, it's even nicer to just escape from them altogether.)

Cheers,
Tom

K7ITM wrote:
:-)

How nice it is to have modern instruments which cover a wide range of
frequencies in one simple measurement setup, display the results in any
of an array of formats, and even store the measurement results for use
in a variety of analysis programs.

(Sometimes, it's even nicer to just escape from them altogether.)

Cheers,
Tom


It's not quite so nice, though, when you develop a psychotic addiction
to measuring which sends you to the poorhouse for buying expensive
equipment, and to the therapist for treatment of your
obsession.
73,
Tom Donaly, KA6RUH