Yuri Blanarovich wrote:
"Richard Clark" wrote

How much better? This sounds like a fractal sales pitch.


Your HOW MUCH is getting a bit TOO MUCH!
Comparing this to fractal sales pitch??? That is TOO MUCH!

He's right, Richard. That was an awfully low blow.

On 20 Apr 2006 06:57:31 -0700, "Bill" wrote:

Yuri Blanarovich wrote:
"Richard Clark" wrote

How much better? This sounds like a fractal sales pitch.


Your HOW MUCH is getting a bit TOO MUCH!
Comparing this to fractal sales pitch??? That is TOO MUCH!

He's right, Richard. That was an awfully low blow.

Yeah, I suppose I should apologize to the fractal crowd.

Tom Ring wrote:
Tom Donaly wrote:

I would prefer a radiator made from half inch PVC filled with a
dilute sodium chloride solution. If you put a valve at the bottom,
it's a snap to adjust resonance.

tom
K0TAR


Have you tried beer?
73,
Tom Donaly, KA6RUH

What!!?? That would be a waste of beer. Well, unless it was Budweiser.

Is there a beer called Budweiser now? Hopefully one to replace that old
PeeWaa that was sold under the same name! ;^)




darn stuff could give me a headache and make me queasy after one
can..... ick.


- 73 de Mike KB3EIA -

wrote in message
oups.com...

Dave wrote:
finally someone said something that makes sense in this thread... but no
one
has addressed my original question directly... but i guess that is par
for
the course in here when this group gets wound up, everyone goes off on
their
own little tangent and starts attacking each other.

I tried to, but I see it did no good at all.

I have a Force 12 80 and 40 meter linear loaded Yagi.

The Q of the loading sections are terrible. They are thin aluminum wire
of some sort of alloy that makes them hard.

For the typical reactances produced by that loading system Q (reactance
over ESR) is well in the sub-100 range.

That's why you can take even a fairly poor loading coil, replace the
linear loading, and have the same perfromance. Or you can make a good
coil, like airdux or BW stock with number 12-14 wire, and make the
antenna work better (IF you can keep it from falling apart in the
wind).

The results of linear loading depends on where the linear loading is
installed and how it is constructed, but the general rule is if you
take the very same size and material conductors and wind a coil it will
work better.

Now I suppose we can talk about UHF antennas, 1/2 inch copper tubing
stubs, Cecil's imaginary reflected waves, quote Harrison's book
collection.....but that's how the Force 12 linear loaded 80 and 40
meter antennas I have work.

That's why they are laying in a pile with waddled out holes near the
rivets and all that lossy linear loading wire wrapped up in a ball,
waiting the be rebuilt into good antennas.

73 Tom

so why would a company like m2 go with linear loading over the much simpler
to build coil? and how in the world do you measure the Q of the loading
section when it is a large percentage of the size of the element? Does Q
even really mean anything in a system that is radiating? Since some of the
energy is being radiated along the length of the loading segment i would
expect it to look very lossy compared to a small coil.

On Thu, 20 Apr 2006 21:38:13 -0000, "Dave" wrote:
so why would a company like m2 go with linear loading over the much simpler
to build coil?

There's no point in explaining market positioning in technical terms,
because they often contradict each other. In other words, the profit
motive does not have to make sense.

and how in the world do you measure the Q of the loading
section when it is a large percentage of the size of the element?

Why would that be difficult?

Does Q
even really mean anything in a system that is radiating?

It does if you want to use it in a trap.

Since some of the
energy is being radiated along the length of the loading segment i would
expect it to look very lossy compared to a small coil.

Good point. The only real issue at hand is I² · Ohmic Loss

73's
Richard Clark, KB7QHC

So Dave, have you built a NEC model of the antenna? Do you know that
the loading stub really has unequal currents on its two legs? Since
that current is fairly close to the element itself, is the net current
(the antenna current) on the stub in phase with or out of phase with
the element current? What about the efficiency reported by NEC--if you
use zero loss conductors versus the loss of the actual aluminum used in
the antenna?

From your description and the picture I found on the m2 website, it
seems to me they are using the stub to make the antenna more
mechanically robust than they could with no support. Whether it causes
poor performance over what could be done with loading coils at the same
positions as the stubs attach or not, I don't know, but a NEC
simulation should shine some light on that question. You could start
with a simple loaded dipole simulation, though that wouldn't tell the
whole story.

I do know that it's unfair to completely discount all stubs because
people misuse them. Even if people regularly misuse them, it's no
reason to discount them: it's reason to learn when they are
appropriate and avoid misusing them. Though I don't know about the
performance of your particular antenna, I do know that stubs can be
very useful in providing reactances and resonators in a variety of
applications, and I do know how to analyze situations in which I use
them.

Cheers,
Tom

Dave wrote:

so why would a company like m2 go with linear loading over the much simpler
to build coil? and how in the world do you measure the Q of the loading
section when it is a large percentage of the size of the element? Does Q
even really mean anything in a system that is radiating? Since some of the
energy is being radiated along the length of the loading segment i would
expect it to look very lossy compared to a small coil.

One of the many very handy things about superposition is that it allows
us to separate the radiating and transmission line properties of a
linear loading section, analyze them separately, and add the results(*).
So the Q of the linear loading section can be determined from its
transmission line properties without radiation being involved. This can
then be directly compared to the Q of a non-radiating inductor. As Tom
W8JI has pointed out, the comparison is often not very favorable to the
linear loaded antenna.

You'd have to ask M2 why they do what they do. I suspect it's because a
lot of amateurs don't understand the loss mechanisms involved, so are
under the mistaken impression that linear loading is less lossy than a
good inductor. And very few amateurs are capable of making even crudely
accurate gain measurements or even comparisons so the vast majority
would never know which is better. Smart companies give the customers
what they want.

(*) This is done by separating the currents on the two conductors into
two sets of currents, common mode -- which radiate -- and differential,
which don't.

Roy Lewallen, W7EL

"Richard Clark" wrote in message
...
On Thu, 20 Apr 2006 21:38:13 -0000, "Dave" wrote:
so why would a company like m2 go with linear loading over the much
simpler
to build coil?

There's no point in explaining market positioning in technical terms,
because they often contradict each other. In other words, the profit
motive does not have to make sense.

reducing cost is a big part of business also, why produce a more complex and
more expensive antenna if you could sell the same performance with a simpler
design? after all, hams are generally cheap.


and how in the world do you measure the Q of the loading
section when it is a large percentage of the size of the element?

Why would that be difficult?

where do you connect your probes? and what are you actually measuring?
since some of the energy is being radiated in between any two points where
you could connect probes or measure currents the thing you are measuring
would exhibit a more resistive (read VERY lossy) characteristic than a small
coil you would put in the 3" gap that the linear loading segment spans where
it connects to the middle of the element. and since the linear loading rods
are not that far from the element itself they will couple strongly to the
inner part of the element.


Does Q
even really mean anything in a system that is radiating?

It does if you want to use it in a trap.

its not a 'trap' its a loading section, meant to make a slightly shorter
than 1/2 wave element resonant. high Q for a trap makes sense, not for a
loading section like this. i think if you base the efficacy of the loading
capability on some notion of Q it will likely be misleading. a better
measure would likely be a field strength comparison.


Since some of the
energy is being radiated along the length of the loading segment i would
expect it to look very lossy compared to a small coil.

Good point. The only real issue at hand is I² · Ohmic Loss

and using relatively large diameter aluminum rod likely has less loss than a
wound coil.


73's
Richard Clark, KB7QHC

On Thu, 20 Apr 2006 23:11:53 -0000, "Dave" wrote:


"Richard Clark" wrote in message
.. .
On Thu, 20 Apr 2006 21:38:13 -0000, "Dave" wrote:
so why would a company like m2 go with linear loading over the much
simpler
to build coil?

There's no point in explaining market positioning in technical terms,
because they often contradict each other. In other words, the profit
motive does not have to make sense.

reducing cost is a big part of business also, why produce a more complex and
more expensive antenna if you could sell the same performance with a simpler
design? after all, hams are generally cheap.

You are confusing a direct correlation between cost and price.
Marketing and demand that rises from marketing determines price, not
cost. Hams pay price which is in excess of cost. This is proven
everyday when they pay for a pre-fab dipole made of two pieces of wire
and three insulators. You don't think they are paying cost for that
alone do you? If so, they would buy two pieces of wire and three
insulators instead.

The profit motive does not have to make sense.

and how in the world do you measure the Q of the loading
section when it is a large percentage of the size of the element?

Why would that be difficult?

where do you connect your probes?

At the source where loss counts. There is no way you are going to
measure unloaded Q if that is your goal - it doesn't matter that much
anyway unless it is for a trap.

I haven't come across any distributed load traps unless someone wants
to stretch meaning to include resonant lines. Even then, the same
answer applies.

and what are you actually measuring?

Q, what else?

since some of the energy is being radiated in between any two points where
you could connect probes or measure currents the thing you are measuring
would exhibit a more resistive (read VERY lossy) characteristic than a small
coil you would put in the 3" gap that the linear loading segment spans where
it connects to the middle of the element. and since the linear loading rods
are not that far from the element itself they will couple strongly to the
inner part of the element.

Ummm, is this a problem? If you want to measure Q and put it in a
bottle, perhaps it is.

Does Q
even really mean anything in a system that is radiating?

It does if you want to use it in a trap.

its not a 'trap' its a loading section, meant to make a slightly shorter
than 1/2 wave element resonant. high Q for a trap makes sense, not for a
loading section like this. i think if you base the efficacy of the loading
capability on some notion of Q it will likely be misleading. a better
measure would likely be a field strength comparison.

Aside from the difficult language, you are not going to find a
scintilla's worth of difference in what you propose to do with an FSM.
It serves the purpose, easily.

As for Q, you need to distinguish between loaded and unloaded Q. Next,
you need to put a metric on what you mean by "high" Q. This is
because you are probably not going to measure anything higher than 8
to 12 for a "slightly shorter than 1/2 wave" antenna. I would find it
remarkable if the unloaded Q of any load would give you something as
bad as a Q in the 20s or 30s.

and using relatively large diameter aluminum rod likely has less loss than a
wound coil.

To say the least, but again, anyone can conspire to fail
magnificently.

73's
Richard Clark, KB7QHC

Dave wrote:
so why would a company like m2 go with linear loading over the much simpler
to build coil?

Marketing, marketing, and marketing.

Manufacturers have done an excellent job making everyone think traps
are lossy and coils are bad. Some companies sell things significantly
worse than what they say is "bad".

One company uses a length of small coaxial line to provide a reactance
loading their antenna to 80 meters, even though a piece of doorbell
wire on a toilet paper tube would have less series resistance for the
same reactance.

Another one markets an antenna they say uses "resonators" instead of
"lossy traps", but when you analyze the resonator it is actually just a
self-resonant coil used as a trap, and that makes ESR terrible compared
to some of the poorest L/C traps we could build.

Linear loading is just another ploy. It lets them say "no lossy coils"
when in effect what you have done is stretch a coil into an elongated
single turn. When you do that you lose the advantage of mutual coupling
aiding in reactance, so you have to increase conductor length to get
the same reactance. A longer current path means more resistance. Worse
yet, the stub places strong electric fields between two conductors
(increases capaciatnce shunting the inductance), and that increases
circulating currents that do nothing but heat the stub while decreasing
bandwidth.

Linear loading is exactly like doing everything we don't want to do to
an inductor...but with one exception. The sole exception is a slight
imbalance in currents allows the stub to radiate a little bit, and that
radiation has the overall effect of allowing the linear loading to move
the effective position of the load insertion to a DIFFERENT location
than the place where the element is insulated.

Say we have a 50 foot long element insulated 12.5 feet from the boom on
each side. If we added linear loading with the stub extended OUTWARDS
from that insulator it would look like we really inserted the loading a
bit further out on the element than the point where the element is
actually broken with an insulator. That can be an advantage because
EFFECTIVE current distribution, the vector sum of current that actually
causes radiation from the stub and element combination, would be more
uniform over distance. We would effectively have more ampere-feet, and
slightly higher radiation resistance.

On the other hand it is just as easy, when we don't understand how the
antenna works, to screw up and fold the loading stub inwards from the
element insulator and move the effective point where the loading is
added closer to the boom.

That's why I say it is a soup of things going on, and the results can
be not as bad as other cases. The general rule is, however, anything we
can do with a linear loading system we can do better with a coil.
Sometimes a little better, sometimes a lot better.

and how in the world do you measure the Q of the loading
section when it is a large percentage of the size of the element?

Substitution and measurement of changes in feedpoint and radiation
charcteristics, formulas to cross check, and dorect measurements of how
the stub itself behaves when balanced.

Does Q
even really mean anything in a system that is radiating?

That's why I defined Q as reactance over ESR, and not the less useful
measurement of bandwidth. When the series resistance increases for a
given reactance, you might as well use the loading system with less
series resistance for the same reactance. That would be an inductor of
proper form factor.

Since some of the
energy is being radiated along the length of the loading segment i would
expect it to look very lossy compared to a small coil.

.....but that radiation does nothing useful, except modify the effective
location where the equivalent lumped load is placed. It doesn't
magically give you something that would otherwise turn to nothing.

I think the picture in your mind is remotely like the seriously flawed
but somewhat popular idea that a folded element has increased
efficiency from increased radiation resistance. 100 feet of wire in a
50 foot linear spatial area is still just a 50 foot antenna. All you
can do is shuffle the effective current distribution around a bit, you
can't make it behave like it is longer than 50 feet, and a coil will do
the same thing for shuffling current as a linear loading system.

All of this aside, the only thing that matters is how happy the antenna
makes people. Doesn't matter that my dipole beats a linear loaded two
element 80 meter Yagi. The yagi impresses people more. My own personal
choice is to use a dipole on the air, but to show people visiting that
I have a 2 element (linear loaded) Yagi.

73 Tom