hi

i was sorta just wondering shooting from the hip (ie not a exact
calculated ans) what happens if you put up a nice inverted v supported
by a center pole of fiberglass vs a metal pole

a) the radation pattern

b) overall swr's and efficiency


big small or no diff?

On Fri, 29 Sep 2006 22:52:09 GMT, ml wrote:

hi

i was sorta just wondering shooting from the hip (ie not a exact
calculated ans) what happens if you put up a nice inverted v supported
by a center pole of fiberglass vs a metal pole
a) the radation pattern

b) overall swr's and efficiency

How did you intend feeding it? Will the feedline look like a vertical
conductor, much like a metal support pole would?

Owen
--

In article ,
Owen Duffy wrote:

On Fri, 29 Sep 2006 22:52:09 GMT, ml wrote:

hi

i was sorta just wondering shooting from the hip (ie not a exact
calculated ans) what happens if you put up a nice inverted v supported
by a center pole of fiberglass vs a metal pole
a) the radation pattern

b) overall swr's and efficiency

How did you intend feeding it? Will the feedline look like a vertical
conductor, much like a metal support pole would?

Owen
--

thanks all, well feedline aside i was only up to the 'mounting' phase
wondering just in theory at that point what it would do (fiberglass vs
metal)

i supposed i would have gotten myself into trouble w/the next question
whats the best way to mount the coax to min it 'interfering' w/the
antenna itself if the ans to the above was fiberglass

my thoughts woulda been to feed it in the center

just really trying to both figure the best performance and trying to
get a mental picture of whats going on the consequence wise

Hello Owen,

You are right, feeding in the middle is good, your feed line is in the
symmetry plane, where you have no E-field component parallel to your
feed line. The line itself will not distort the radiation pattern.

When it is a halve wave mono band antenna I would use a coaxial feeder
with balun (current mode balun with ferrite cores for example).

When the antenna has to work over multiple bands, you get problems with
the impedance when your dipole is a full wave. Matching the coaxial
feeder/balun combination will make almost sure all your power will be
wasted in the form of heat in the balun and or the coaxial feeder. In
that case I would prefer a symmetrical line (can have extremely low
loss) and a symmetrical tuner.

When one end of the dipole is close to ground or a large metal
structure, you may feed the dipole at that end as an alternative. When
your dipole is a multiple of halve a wavelength, the input impedance at
the ends is in the high kOhm range. So you will have a relative low
feed current and therefore also low ground current (so the ground can
be relatively bad).

I hope this and the other replies will help you to make good decision
on what to do.

Wim
PA3DJS.

In article .com,
"Wimpie" wrote:

Hello Owen,

You are right, feeding in the middle is good, your feed line is in the
symmetry plane, where you have no E-field component parallel to your
feed line. The line itself will not distort the radiation pattern.

When it is a halve wave mono band antenna I would use a coaxial feeder
with balun (current mode balun with ferrite cores for example).

When the antenna has to work over multiple bands, you get problems with
the impedance when your dipole is a full wave. Matching the coaxial
feeder/balun combination will make almost sure all your power will be
wasted in the form of heat in the balun and or the coaxial feeder. In
that case I would prefer a symmetrical line (can have extremely low
loss) and a symmetrical tuner.

When one end of the dipole is close to ground or a large metal
structure, you may feed the dipole at that end as an alternative. When
your dipole is a multiple of halve a wavelength, the input impedance at
the ends is in the high kOhm range. So you will have a relative low
feed current and therefore also low ground current (so the ground can
be relatively bad).

I hope this and the other replies will help you to make good decision
on what to do.

Wim
PA3DJS.

yes thank you it will i appreciate everyones help it will allow me to
narrow down my guesses and know a bit better what to expect for sure

wish there was classes on this stuff


i dunno experimenting around with antennas is a lot of fun

ml

I know from various documents written by amateurs that there is a lot
of antenna related expertise within the Amateur Ccommunity (from which
I believe many are professionals). Many times it is difficult to
figure out who is telling "the facts".

Regarding classes, I am sure there are, but mostly are very expensive.
In the Netherlands there are a few companies that offer courses on
antenna design. Sometimes they are cancelled because of lack of
attendees.

With respect to books, many books tell you how to build an antenna from
a drawing (and not the theory behind it), other books tell you the
theory behind it, but require differential vector calculus.

It took me many years to understand antennas at the same level as my
electronic design activities.

Given all this, ¡I still like experimenting with antennas! I just
finished a design for the coming "Jamboree on the Air" to be held
during the weekend of 22 October (Scouting activity).

Best Regards,

Wim
PA3DJS

ml ha escrito:

hi

i was sorta just wondering shooting from the hip (ie not a exact
calculated ans) what happens if you put up a nice inverted v supported
by a center pole of fiberglass vs a metal pole

a) the radation pattern

b) overall swr's and efficiency


big small or no diff?

When you feed your (halve wave) inverted V in the middle (top) via a
balun, there will be no difference.

When you feed it at one end (with respect to ground) there will be
some asymmetry in the antenna causing some net effect in the metal
post. As long as the wire does not touch the post and the post is in
the voltage minimum, the effect on the radiaton pattern and efficiency
is negligible. Maybe you have to adjust the length a little bit.

Wim
PA3DJS

ml wrote:
hi

i was sorta just wondering shooting from the hip (ie not a exact
calculated ans) what happens if you put up a nice inverted v supported
by a center pole of fiberglass vs a metal pole

a) the radation pattern

b) overall swr's and efficiency


big small or no diff?

Very small difference all the way around.
I prefer metal masts because they are better lightning
returns. I'd rather have the metal mast taking the brunt of
the strike to ground rather than the feedline of an antenna.
MK