OK, I gotta take issue with the part that says,

" A transmission line, even a very good one, generally has a Q of
someplace around 20-75. The definition of Q I am using is reactance
over ESR. Say you need a reactance of 400 ohms to resonate an antenna.
Linear or stub loading would add a series resistance of 5 to 20 ohms as
loss resistance at that point in the system.
"

I know that transmission line Q varies all over the place: it's much
more reasonable to use it in a resonator at high frequencies than low,
and line construction makes a big difference too. To back this up with
numbers, I just ran some calcs (actually put together a little Scilab
program to run them for me) on four different lines: (a) is RG-8/RG-213
type line with solid poly dielectric, (b) is 75 ohm air insulated coax
in an 0.5" ID copper tube, (c) is balanced two-wire line made with
12AWG (~2mm) wire spaced 2" (~5cm) on centers), and (d) is two 0.625"
OD copper tubes spaced 3" on center.

For a 1/8 wave section of line shorted at the far end, the calculated
impedances and Qs a

line a, 10MHz: 0.622+j50, Q=80
line a, 100MHz: 0.197+j50, Q=254
line a, 1000MHz: 0.0622+j50, Q=800

line b, 10MHz: 0.35+j75, Q=215
100MHz: 0.110+j75, Q=679
1GHz: 0.035+j75, Q=2147

line c, 10MHz: 0.972+j469, Q=482
100MHz: 0.307+j469, Q=1526
1GHz * : 0.097+j469, Q=4826

line d, 10MHz: 0.124+j270, Q=2170
100MHz: 0.039+j270, Q=6864
1GHz * : 0.012+j270, Q=21.7k

* -- the open wire lines will likely not work in practice quite this
well at UHF...

With luck, I got all the calcs right; but in any event, I do expect the
Q to go up for a given stub as the sqrt(f), and the Q of open-wire
lines to be considerably higher than that of coax with similar
conductor diameter, just because the impedance is higher.

The Q of an RG-8-type stub at 10MHz isn't wonderful, but at higher
frequencies and with different construction, stubs can work better than
coils. There is a range of frequencies where it can be a matter of
construction preference: the stub may be easier to integrate into a
design, or the coil may be, depending. At high enough frequencies, the
stub often is easier.

Also, I want to point out that in a collinear -- a half-wave dipole,
center fed, in the center, and an additional half-wave element on
either end, coupled through a two-wire-line stub perpendicular to the
antenna performs distinctly better than the same antenna in which the
stubs are replaced by self-resonant coils, or by a coaxial stub which
is made to be collinear with the antenna. That's because the
perpendicular stub interacts with the antenna field to excite the right
mode on the line to get substantial current in the outboard collinear
half-waves. See King for further explanation.

Cheers,
Tom

wrote:
Dave wrote:
How would you guys who are stuck in an endless thread of loading coils like
to take on 'linear loading'?? are the currents the same at each end of the
loading line?? do they cancel completely along the length of the loading
line? does the loading line replace so many degrees of the length of the
elements or cause some kind of delay???


All of the petty arguing and self-promotion aside, linear loading is
just a very poor form of a loading coil. Like any poorly designed
system, the ill effects of design shortfalls can range from very small
to very large.

As a general rule, linear loading reduces efficiency over a lumped coil
of good design. Again the exact amount and the overall effect varies
with where the loading is placed in the antenna, how it is constructed,
and where and how the loading coil compared to it is constructed and
placed.

A transmission line, even a very good one, generally has a Q of
someplace around 20-75. The definition of Q I am using is reactance
over ESR. Say you need a reactance of 400 ohms to resonate an antenna.
Linear or stub loading would add a series resistance of 5 to 20 ohms as
loss resistance at that point in the system.

It would take a very poor coil to have that Q, but it can be done.

Depending on where in the antenna you insert that loss resistance, the
effects can be large or small. Myself, I avoid linear loading. I'm not
a person who likes to gamble.

We have now all seen first hand how a fascination with destroying
others really just destroys the ability to learn anything ourselves
and to help others learn. This loading coil thing has become a mental
illness, like uncontrolled shoplifting. One fellow wrote a nice book on
transmission lines and a long argument about amplifiers and a long
argument about reflected waves on amplifiers did the same thing.

This stuff is more a demonstration of emotional problems or mental
illness than science and education. It's one step below someone going
postal and just shooting everyone else in the world who is responsible
for his failures and unpopularity!

I hope this post gives insight into how arguing or fixations ruin the
educational process, and also sheds light on linear loading. Something
for everyone.

73 Tom

Chrystos Voskres! Christ has risen!

May he nelighten those confused and enlighten them!

Nice going Tom, W8JI!

73 Yuri, K3BU.us

On 16 Apr 2006 15:44:06 -0700, "K7ITM" wrote:

OK, I gotta take issue with the part that says,

" A transmission line, even a very good one, generally has a Q of
someplace around 20-75. The definition of Q I am using is reactance
over ESR. Say you need a reactance of 400 ohms to resonate an antenna.
Linear or stub loading would add a series resistance of 5 to 20 ohms as
loss resistance at that point in the system.
"

I know that transmission line Q varies all over the place: it's much
more reasonable to use it in a resonator at high frequencies than low,
and line construction makes a big difference too. To back this up with
numbers, I just ran some calcs (actually put together a little Scilab
program to run them for me) on four different lines: (a) is RG-8/RG-213
type line with solid poly dielectric, (b) is 75 ohm air insulated coax
in an 0.5" ID copper tube, (c) is balanced two-wire line made with
12AWG (~2mm) wire spaced 2" (~5cm) on centers), and (d) is two 0.625"
OD copper tubes spaced 3" on center.

For a 1/8 wave section of line shorted at the far end, the calculated
impedances and Qs a

line a, 10MHz: 0.622+j50, Q=80
line a, 100MHz: 0.197+j50, Q=254
line a, 1000MHz: 0.0622+j50, Q=800


I tried these numbers in the line loss calculator at
http://www.vk1od.net/tl/tllce.php using Belden 8267 of 2.475m length
for 0.125 wavelengths and Zload=0.0000000001. The input Z I got was a
little higher at 0.88+j50 (probably slightly different approximation
of Zo used in the calcs), yeilding a Q of 57. The Q is quite dependent
on line length, decreasing as length increases towards a quarter wave.

I suspect this is not a good method of analysing behaviour when the
line elements are field coupled to other radiator elements, the
currents in each leg are not necessarily equal and opposite.

Owen
--

Yes, the Q as determined by simply taking X/R decreases as you approach
1/4 wavelength, but what you really need to do is resonate it with a
capacitance and look at the Z as a function of frequency when you do
that. I mean, it IS a resonator if it's 1/4 wave long: it would look
like Q=0 there if you take X/R, but of course it's not. If you simply
want _inductance_ (i.e. a loading coil), do NOT make the stub close to
1/4 wave long. It's just the same as trying to use a coil for
inductance up near its self-resonance.

Also, a point that was in my mind when I originally posted, but failed
to put well into writing then, is that as frequency increases, the Q of
a solenoid coil will increase about as the square root of
frequency...and the size stays the same. But the stub's Q also
increases as the square root of frequency, while it's size (length) is
directly proportional to 1/freq, and it's shrinking in size.

And thanks for the cross-check on my numbers, Owen. I hacked it pretty
quickly, and may have missed a cog somewhere, though I think the
numbers are reasonably close. I suppose one of Reg's programs will
give you stub impedance, too. -- I think I see why my numbers may be
a bit different than what you got; I'll check on it as I have time,
though the difference isn't enough to worry me--the trends are still
the same.

Cheers,
Tom

Owen Duffy wrote:
On 16 Apr 2006 15:44:06 -0700, "K7ITM" wrote:

OK, I gotta take issue with the part that says,

" A transmission line, even a very good one, generally has a Q of
someplace around 20-75. The definition of Q I am using is reactance
over ESR. Say you need a reactance of 400 ohms to resonate an antenna.
Linear or stub loading would add a series resistance of 5 to 20 ohms as
loss resistance at that point in the system.
"

I know that transmission line Q varies all over the place: it's much
more reasonable to use it in a resonator at high frequencies than low,
and line construction makes a big difference too. To back this up with
numbers, I just ran some calcs (actually put together a little Scilab
program to run them for me) on four different lines: (a) is RG-8/RG-213
type line with solid poly dielectric, (b) is 75 ohm air insulated coax
in an 0.5" ID copper tube, (c) is balanced two-wire line made with
12AWG (~2mm) wire spaced 2" (~5cm) on centers), and (d) is two 0.625"
OD copper tubes spaced 3" on center.

For a 1/8 wave section of line shorted at the far end, the calculated
impedances and Qs a

line a, 10MHz: 0.622+j50, Q=80
line a, 100MHz: 0.197+j50, Q=254
line a, 1000MHz: 0.0622+j50, Q=800


I tried these numbers in the line loss calculator at
http://www.vk1od.net/tl/tllce.php using Belden 8267 of 2.475m length
for 0.125 wavelengths and Zload=0.0000000001. The input Z I got was a
little higher at 0.88+j50 (probably slightly different approximation
of Zo used in the calcs), yeilding a Q of 57. The Q is quite dependent
on line length, decreasing as length increases towards a quarter wave.

I suspect this is not a good method of analysing behaviour when the
line elements are field coupled to other radiator elements, the
currents in each leg are not necessarily equal and opposite.

Owen
--

You dim witts are calculating Q incorrectly.

Q = X / R

where R is the RF resistance of the conductor and X is the reactance
of the conductor's inductance. You first have to calculate
inductance.

You get a high Q at resonance.
----
Reg, G4FGQ

On Mon, 17 Apr 2006 08:41:36 +0100, "Reg Edwards"
wrote:

You dim witts are calculating Q incorrectly.


Reg, that is just so polite!

Q = X / R

where R is the RF resistance of the conductor and X is the reactance
of the conductor's inductance. You first have to calculate
inductance.


So, you state that the ratio X/R is an acceptable way to express the Q
of an inductor, why is it unacceptable to express the Q of a two
terminal device with an equivalent series impedance of 0.88+j50 (where
0.88 is the RF series resistance of the network and 50 is the series
inductive reactance of the element) as 50/0.88 or 57?

Aren't the effiency implications (for that was the context) for a 50
ohm reactance created with a TL stub as described just the same as for
a coil with 50 ohms of inductive reactance and 0.88 ohms of series
(RF) resistance, ie a coil with the same Q factor?

Owen
--

"Owen Duffy" wrote in message
...
On Mon, 17 Apr 2006 08:41:36 +0100, "Reg Edwards"
wrote:

You dim witts are calculating Q incorrectly.


Reg, that is just so polite!

Q = X / R

where R is the RF resistance of the conductor and X is the
reactance
of the conductor's inductance. You first have to calculate
inductance.


So, you state that the ratio X/R is an acceptable way to express the
Q
of an inductor, why is it unacceptable to express the Q of a two
terminal device with an equivalent series impedance of 0.88+j50
(where
0.88 is the RF series resistance of the network and 50 is the series
inductive reactance of the element) as 50/0.88 or 57?

Aren't the effiency implications (for that was the context) for a 50
ohm reactance created with a TL stub as described just the same as
for
a coil with 50 ohms of inductive reactance and 0.88 ohms of series
(RF) resistance, ie a coil with the same Q factor?

Owen
----------------------------------------------------------------------
---
Owen,
Please excuse my mild scold.

There is only ONE way to calculate Q of a coil or a wire and that is
the way I have described.

It is the ratio of inductive reactance to resistance of the wire, in
series with other. They cannot be measured in combination with each
other.

To do so results in something altogether different like measuring the
input impedance of an antenna at or near resonance where the inductive
reactance is tuned out by the capacitance and is therefore NOT
measured.

It is elementary my dear Watson.
----
Reg.

Reg, old sot, you need to either quit drinking so much or go back to
the fundamental definition of Q. The Q of a coil or capacitor is
always an abstraction from the definition. In any event, trying to use
a coil or a stub at or near its self (anti)resonance to get an
inductive reactance is a really bad plan. You can't separate the
self-capacitance from the coil or the stub, so assuming only the
reactance from the wire's inductance does you no good at all in that
case. As a resonator, it's fine. As an inductive loading component
(which is the topic of this thread), it sucks.

Cheers,
Tom

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?)