I want to construct a 80-40-20 meter dipole, but want to trap the 80 meters to
shorten the length. Does anyone know where I can get good quality traps? I am a
beginner as far as antenna theory.

Vinnie S.

for an 80-40-20 dipole you don't need 'traps' to shorten the 80m piece you
need 'loading coils'. 'traps' have a resonance that effectively cuts off
the section of the wire past them making the inner part resonant on the
higher frequency, so you need 'traps' for 20m and 40m. 'loading coils' are
simply an inductance that makes the section appear longer than it physically
is.

"Vinnie S." wrote in message
...
I want to construct a 80-40-20 meter dipole, but want to trap the 80 meters
to
shorten the length. Does anyone know where I can get good quality traps? I
am a
beginner as far as antenna theory.

Vinnie S.

Traps will not shorten your antenna appreciably. To shorten an antenna,
you use loading coils, which are just wires turned into a coil. Traps
consist of a coil and a capacitor in parallel with each other that stop
signal flow through them at a specific frequency.

So, if I understand what you want, is that you want the total antenna
length to be shorter than a normal half-wave dipole on 80M. The best
place to find the info you seek is in the ARRL Antenna Handbook. They
should be available at http://www.arrl.org/

You will first need to determine what length you want the antenna for
80M to be. Then, you will want to look in the chart in the book. You
will want to place the coils as far out from the center of the antenna
as practical. The further out the loading coils are from center, the
larger amount of inductance they need to be to a point where it is
impractical to build them. Usually putting them at the 50% point is
fairly easy but, if you are going to have a 40M trap in the antenna,
these would be right about where the loading coils would go, so, just
move the loading coils outward from center, just a few feet past the 40M
traps. You will most likely have to adjust the wire lengths from the
loading coils out to the ends of the antenna to find resonance.

Scott
N0EDV



Vinnie S. wrote:

I want to construct a 80-40-20 meter dipole, but want to trap the 80 meters to
shorten the length. Does anyone know where I can get good quality traps? I am a
beginner as far as antenna theory.

Vinnie S.

He wants multi band operation. Therefore he needs traps to provide the
necessary isolation for 40 and 20 meters.

Dave wrote:

for an 80-40-20 dipole you don't need 'traps' to shorten the 80m piece you
need 'loading coils'. 'traps' have a resonance that effectively cuts off
the section of the wire past them making the inner part resonant on the
higher frequency, so you need 'traps' for 20m and 40m. 'loading coils' are
simply an inductance that makes the section appear longer than it physically
is.

"Vinnie S." wrote in message
...

I want to construct a 80-40-20 meter dipole, but want to trap the 80 meters
to
shorten the length. Does anyone know where I can get good quality traps? I
am a
beginner as far as antenna theory.

Vinnie S.

that is what i said, but in regards to 'shorten the length' of the 80m part
it is a loading coil he needs.

"Ham op" wrote in message
...
He wants multi band operation. Therefore he needs traps to provide the
necessary isolation for 40 and 20 meters.

Dave wrote:

for an 80-40-20 dipole you don't need 'traps' to shorten the 80m piece
you need 'loading coils'. 'traps' have a resonance that effectively cuts
off the section of the wire past them making the inner part resonant on
the higher frequency, so you need 'traps' for 20m and 40m. 'loading
coils' are simply an inductance that makes the section appear longer than
it physically is.

"Vinnie S." wrote in message
...

I want to construct a 80-40-20 meter dipole, but want to trap the 80
meters to
shorten the length. Does anyone know where I can get good quality traps?
I am a
beginner as far as antenna theory.

Vinnie S.

On Sun, 4 Sep 2005 12:18:40 -0000, "Dave" wrote:

that is what i said, but in regards to 'shorten the length' of the 80m part
it is a loading coil he needs.

The traps -do- shorten the overall length of the antenna. Because the
80-meter part -is- the total length, I would say the traps shorten it.
In other words, below their resonant frequency they are inductive and
function as loading coils.

The usual configuration of an 80-40 trap dipole has 40 Meter traps at
about 33 feet from the center. The remaining wire is less than for a
full half wave on 80 Meters since the 40 Meter trap acts as a loading
coil on 80. Length may be less if you have 20 Meter traps as well.

If you have enough room for a little over 100 feet, you may not need
any additional loading coils. You also might reduce the total length
some by increasing the inductance-to-capacitance ratio of the traps.


I don't think he will have any problem getting that antenna in at under
100 feet with out using extra inductance at the ends. My 75M dipole
trapped at 40M is right around 100 feet, I think. If he adds 20M traps
they will surly shorten it even more.


Ed

On Sat, 03 Sep 2005 23:04:48 -0400, Vinnie S. wrote:

I want to construct a 80-40-20 meter dipole, but want to trap the 80 meters to
shorten the length. Does anyone know where I can get good quality traps? I am a
beginner as far as antenna theory.

Vinnie S.


Thanks for all the responses, but I seem to be more confused because it seemed I
got differing opinions. As I said, I am a beginner at antenna theory. The
frequencies I am trying to make an antenna for, are centered at 3.875, 7.225,
and 14.250. Those are the center for the phone frequencies on the US bands. I
wanted to shorten the 80 meter band antenna. I would have kept the 40 and 20 at
the specified lengths. I guess I will buy the ARRL book. But they also make a
long wire classic book. I might get that instead. .

Vinnie S.

In article , Vinnie S.
wrote:
Thanks for all the responses, but I seem to be more confused because it
seemed I
got differing opinions. As I said, I am a beginner at antenna theory. The
frequencies I am trying to make an antenna for, are centered at 3.875, 7.225,
and 14.250. Those are the center for the phone frequencies on the US bands. I
wanted to shorten the 80 meter band antenna. I would have kept the 40
and 20 at
the specified lengths. I guess I will buy the ARRL book. But they also make a
long wire classic book. I might get that instead. .

Vinnie-

One thing isn't clear. How short do you need the total length to be?

I think everyone is in agreement that a trap dipole is shorter on the
lower band than a simple dipole would be for that band. The trap acts
like an inductor below its resonant frequency, so the part of the antenna
beyond the trap is electrically lengthened on the lower band(s).

Therefore, the 20 Meter traps would be at the proper places, around 16
feet each side of center. However, the 40 Meter traps would be closer to
the center than for a simple dipole, due to the inductive effect of the 20
Meter traps. Similarly, the added wire for 80 Meters is less than for a
simple dipole due to both the 20 and 40 Meter traps' inductance.

You may find that the resulting length of a dipole with both 20 and 40
Meter traps, is short enough for your needs.

73, Fred, K4DII

You are correct and asked the proper question.

HOW SHORT DO YOU WANT THE FINAL ANTENNA TO BE??

Fred McKenzie wrote:
In article , Vinnie S.
wrote:

Thanks for all the responses, but I seem to be more confused because it

seemed I

got differing opinions. As I said, I am a beginner at antenna theory. The
frequencies I am trying to make an antenna for, are centered at 3.875, 7.225,
and 14.250. Those are the center for the phone frequencies on the US bands. I
wanted to shorten the 80 meter band antenna. I would have kept the 40

and 20 at

the specified lengths. I guess I will buy the ARRL book. But they also make a
long wire classic book. I might get that instead. .


Vinnie-

One thing isn't clear. How short do you need the total length to be?

I think everyone is in agreement that a trap dipole is shorter on the
lower band than a simple dipole would be for that band. The trap acts
like an inductor below its resonant frequency, so the part of the antenna
beyond the trap is electrically lengthened on the lower band(s).

Therefore, the 20 Meter traps would be at the proper places, around 16
feet each side of center. However, the 40 Meter traps would be closer to
the center than for a simple dipole, due to the inductive effect of the 20
Meter traps. Similarly, the added wire for 80 Meters is less than for a
simple dipole due to both the 20 and 40 Meter traps' inductance.

You may find that the resulting length of a dipole with both 20 and 40
Meter traps, is short enough for your needs.

73, Fred, K4DII