Excuse me for my ignorance of antenna modelling and EZNEC models.
I've been following this lumped coils stuff and bugcatcher loading
coils, as many others, just to learn on the theory.

So far, I've learned on computer models and on Kraus theories.

Please light my candle:

Something I am missing: I'm thinking about how a trap antenna works:
The trap is resonant isn't it? On the frequency of interest: Say 75m.

On a trap dipole, there is a reduction of current flowing on the other
side of the trap ? Because it is a resonnant circuit made of L and C.

If someone would put current meters on each side of the trap, what
would he measure ? A reduction of the current ?

On a Bugcatcher coil, isn't this is what is happening? The coil is
usually tuned after the antenna is installed ? The Bugcatcher coil is
acting ilke a trap ?

The capacitance of the trap is between the car body and the coil,
isn't it?

So would a properly adjusted Bugcatcher coil show a reduction of the
current. Isn't that what we would like to achieve ?

Stef

The difference between the trap and loading coil is this:

Loading coil "shortens" the radiator physical length by replacing the portion
of the radiator with inductance. Current on the ends of the coil is more-less
as it would be if there was a wire that coil replaces.

Trap typically resonates (by self resonance or with aid of parallel capacitor)
on the operating frequency of the portion of radiator between the feedpoint and
the the trap. It presents high impedance and practically isolates rest of the
radiator beyond the trap. On other frequencies (lower) it becomes loading coil
"connecting" the rest of the radiator and at the same time shortening its
physical length.

So the coil is a coil. In DC circuits behaves as flat earth believers want it
to behave in AC circuits. In RF curcuits, the current distribution depends on
the frequency and position of the coil along the radiator.

Check my web page for the start of the argument and some explanations
www.K3BU.us

Yuri, K3BU

Stef wrote:
On a Bugcatcher coil, isn't this is what is happening? The coil is
usually tuned after the antenna is installed ? The Bugcatcher coil is
acting ilke a trap ?

A trap is operated at its resonant frequency. A bugcatcher
coil is supposed to be operated far below its self-resonant
frequency. So the bugcatcher is a lower impedance than a
trap and doesn't impede the current as much as a trap.

A trap operated at 1/2 its resonant frequency is primarily
inductive, like a bugcatcher coil.
--
73, Cecil, W5DXP

Traps are "resonant" loading coils are not.

The theory of a trap is as follows. Take an antenna for one band, say a
half wave dipole on 40M. To add another band lower in freq, say 80M you
need more length, right? If you add it, then the first band is off, but if
you can add the length and remove it every time you are on the higher band
you are ok again.
A parallel resonant circuit is a high impedance at its resonant
frequency...so put a parallel L & C, resonant at 40M on the end of the 40M
dipole and add the length on the other side. Since the L/C is resonant =
high Z, it is like an open circuit.
On 80M the L/C is not resonant, so it is a "low" impedance and the added
wire is now connected.
Side note: since the Z of the antenna is pretty high at the ends, this L/C
better have a really good Q (low loss & therefore a really high Z) so it
effectively looks like an open (or nearly so) circuit and the extra wire has
minimal effect on the 40M behavior.

Since the trap is an L/C it has does have some Z on 80M (though we really
didn't want this) and it will be the combination of the L&C which will be
inductive. SO you have a coil at this point on your 80M antenna and will
have to adjust the wire length appropriately.
BTW, at this point, (even though this is not what we wanted) this coil
happens to have a loading coil effect on the 80M band...see next.

Theory of a loading coil.
When we can't make an antenna long enough to get to the full resonant length
(1/2 or 1/4 depending on the style) we have found that putting a
coil/inductor (which looks inductive) into the antenna, we can find an
inductance which gets the thing resonant and sometimes help the feed point
resistance get closer to the desired 50 ohms.

That's the basic difference
--
Steve N, K,9;d, c. i My email has no u's..



"Stef" wrote in message
...
Excuse me for my ignorance of antenna modelling and EZNEC models.
I've been following this lumped coils stuff and bugcatcher loading
coils, as many others, just to learn on the theory.

So far, I've learned on computer models and on Kraus theories.

Please light my candle:

Something I am missing: I'm thinking about how a trap antenna works:
The trap is resonant isn't it? On the frequency of interest: Say 75m.

On a trap dipole, there is a reduction of current flowing on the other
side of the trap ? Because it is a resonnant circuit made of L and C.

If someone would put current meters on each side of the trap, what
would he measure ? A reduction of the current ?

On a Bugcatcher coil, isn't this is what is happening? The coil is
usually tuned after the antenna is installed ? The Bugcatcher coil is
acting ilke a trap ?

The capacitance of the trap is between the car body and the coil,
isn't it?

So would a properly adjusted Bugcatcher coil show a reduction of the
current. Isn't that what we would like to achieve ?

Stef

On Fri, 06 Feb 2004 12:05:09 -0500, Stef
wrote:
If someone would put current meters on each side of the trap, what
would he measure ? A reduction of the current ?

On a Bugcatcher coil, isn't this is what is happening? The coil is
usually tuned after the antenna is installed ? The Bugcatcher coil is
acting ilke a trap ?

Hi Stef,

Your confusion arises from trying to learn via the internet where ALL
answers are available (especially here). To avoid confusion, you need
to establish a reference point, something you can trust. With
modelers, you can start simple and progress to issues of more
complexity. This instruction is inductive, which means (employing our
EE term instead of the common English usage of the term) it can boost
your understanding, or it can impede it. Thus it pays to find a good
traditional source to enlarge the deductive side of understanding
(usually a good book or correspondence/conversation).

Philosophy aside, coils as parts of a radiating structure come in two
flavors - you have already noted and described them above (if
incompletely): traps and loads (which may also be traps).

The controversy over coils that is currently raging (all puns
intended) focus on the coil acting as a replacement length to a short
antenna. These loads are not traps. Such loads, or loading coils,
attempt to create a higher flow of current through them to achieve
resonance.

Traps imply through language an element that stops. Traps are
parallel resonant elements that are high-Z in series to the adjacent
sections of the antenna. They trap (stall, stop, impede) currents
from proceeding through them to the other section on the farther side.
Hence they are used with antennas that are larger than necessary.
This makes them frequency selective, open switches that disconnect
excess length from the resonant shorter sections.

So there you have the duality of short-antenna/load and
long-antenna/trap.

Then we progress to where the trap may become a load (in the sense of
lengthening a too short antenna). In this function, the coil/cap
combination is no longer resonant alone, but within the parasitics of
the larger structure (which also exhibits capacitance) it becomes
resonant. In this sense, the trap becomes part of a series resonance
and is no longer impeding flow.

Hence there is another duality to consider: series-resonance/short and
parallel-resonance/long.

The use of an element (coil/capacitor) as trap (parallel resonant) AND
load (series resonant) gives you opportunistic designs that allow one
tuned element (still speaking of the coil/capacitor) to offer more
than two band operation. Traditionally, the trap splits the radiating
structure into two band operation; additionally, the sections that are
thus physically split may also resonate (with the now incorrectly
named trap) in series in a third band. This opportunistic arrangement
may also reveal dual band operation of quarterwave sections driving
halfwave sections (or other combinations) for single band, gain
antennas.

When you get into this kind of sophistication, it often turns on
juggling many variables to achieve this legerdemain. You can either
approach it cookbook style or through a modeler.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Fri, 06 Feb 2004 12:05:09 -0500, Stef
wrote:
If someone would put current meters on each side of the trap, what
would he measure ? A reduction of the current ?

On a Bugcatcher coil, isn't this is what is happening? The coil is
usually tuned after the antenna is installed ? The Bugcatcher coil is
acting ilke a trap ?

Hi Stef,

Your confusion arises from trying to learn via the internet where ALL
answers are available (especially here). To avoid confusion, you need
to establish a reference point, something you can trust. With
modelers, you can start simple and progress to issues of more
complexity. This instruction is inductive, which means (employing our
EE term instead of the common English usage of the term) it can boost
your understanding, or it can impede it. Thus it pays to find a good
traditional source to enlarge the deductive side of understanding
(usually a good book or correspondence/conversation).

Philosophy aside, coils as parts of a radiating structure come in two
flavors - you have already noted and described them above (if
incompletely): traps and loads (which may also be traps).

The controversy over coils that is currently raging (all puns
intended) focus on the coil acting as a replacement length to a short
antenna. These loads are not traps. Such loads, or loading coils,
attempt to create a higher flow of current through them to achieve
resonance.

Traps imply through language an element that stops. Traps are
parallel resonant elements that are high-Z in series to the adjacent
sections of the antenna. They trap (stall, stop, impede) currents
from proceeding through them to the other section on the farther side.
Hence they are used with antennas that are larger than necessary.
This makes them frequency selective, open switches that disconnect
excess length from the resonant shorter sections.

So there you have the duality of short-antenna/load and
long-antenna/trap.

Then we progress to where the trap may become a load (in the sense of
lengthening a too short antenna). In this function, the coil/cap
combination is no longer resonant alone, but within the parasitics of
the larger structure (which also exhibits capacitance) it becomes
resonant. In this sense, the trap becomes part of a series resonance
and is no longer impeding flow.

Hence there is another duality to consider: series-resonance/short and
parallel-resonance/long.

The use of an element (coil/capacitor) as trap (parallel resonant) AND
load (series resonant) gives you opportunistic designs that allow one
tuned element (still speaking of the coil/capacitor) to offer more
than two band operation. Traditionally, the trap splits the radiating
structure into two band operation; additionally, the sections that are
thus physically split may also resonate (with the now incorrectly
named trap) in series in a third band. This opportunistic arrangement
may also reveal dual band operation of quarterwave sections driving
halfwave sections (or other combinations) for single band, gain
antennas.

When you get into this kind of sophistication, it often turns on
juggling many variables to achieve this legerdemain. You can either
approach it cookbook style or through a modeler.

73's
Richard Clark, KB7QHC

Hello Richard

"Your confusion arises from trying to learn via the internet where ALL
answers are available (especially here)."

ROTFLMAO

And to Stef and the Assembled Multitudes:

"You can either approach it cookbook style or through a modeler."

I would add that you can derive a lifetime ......
(I'm near 50 years since my first crystal set.)
.......of entertainment by building antennas and comparing them to one
another.

73
H.
NQ5H

I would add that you can derive a lifetime ......
(I'm near 50 years since my first crystal set.)
......of entertainment by building antennas and comparing them to one
another.

That's my situation !

Thanks to all .

Now I understand the loading coils on a bugcatcher are not resonnant,
they're just loading coils.

I've built traps before for an 80m / 40m dipole. I don't have the
space for it here, but I'll try my hand on an 80m / 40m vertical with
top hat soon.

I've learned from books first, then by following the internet,
discussions about the subjects, I find other ways of looking into
things. It sure is fun to read what others are saying.

On Sat, 07 Feb 2004 09:53:43 -0500, Stef
wrote:
Now I understand the loading coils on a bugcatcher are not resonnant,
they're just loading coils.

Hi Steff,

They ARE resonant, otherwise what's the point in using one?

A short antenna exhibits a principally capacitive reactance that with
the addition of a loading coil resonates the structure leaving only
the radiation resistance behind.

73's
Richard Clark, KB7QHC

Now I understand the loading coils on a bugcatcher are not resonnant,
they're just loading coils.



They ARE resonant, otherwise what's the point in using one?

A short antenna exhibits a principally capacitive reactance that with
the addition of a loading coil resonates the structure leaving only
the radiation resistance behind.

73's
Richard Clark, KB7QHC



They are NOT resonant at the frequencies of interest - making antenna resonate
on that frequency. If they were, they would act as a trap and "disconnect" rest
of the whip beyond the coil. And that's the truth, fact, reality. Uh, huh?

Yuri, K3BU.us

On 07 Feb 2004 18:43:31 GMT, oUsama (Yuri Blanarovich)
wrote:

They are NOT resonant at the frequencies of interest
That is like saying the coil in a tank is not resonant by looking at
the coil alone.

What a myopic way of looking at antenna design.

Loading coils are SERIES RESONANT, traps are PARALLEL RESONANT.

The only difference is where the capacitor is. For a loading coil,
the capacitor is made up of the reactance of a too short antenna. For
a trap, there is a literal capacitor, AND the reactance of the
antenna.

If the antenna had no reactance, there would be no need for the
loading coil (unless it is your next patent-applied for snow removal
device).

73's
Richard Clark, KB7QHC