Metal mast for inverted V antenna support--will it work?
 

What is the result of using a metal mast as the center support of an inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR

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Metal mast for inverted V antenna support--will it work?
 

wrote:

What is the result of using a metal mast as the center support of an inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR
There must be a million hams using their towers as the center support for
their vees. In theory the tower is at the electrical center and has little
or no effect. At least this is my theory!!! There are a few pundits who might
want to argue the point.

Irv VE6BP

Metal mast for inverted V antenna support--will it work?
 

wrote in message ...
What is the result of using a metal mast as the center support of an
inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR

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No problem at all. I use a steel telescopic pylon, 20 m long.

It supports two inverted V's: one for 40 m and one for 80 m. The wires are
kept 20 cm apart by 5/8" plastic tubing. The two inverted V's are fed in
parallel through a 1/4 balun at the end of a 50 ohms cable.

VSWR is almost 1/1 for 40 m. On 80 m the VSWR varies from 1/1 to 1,8/1.

At least 200 kHz of the 80 m band can be within 1,5/1. Of course, the length
of the elements determines witch part of the band that is.

Metal mast for inverted V antenna support--will it work?
 

"Philo" wrote in message
...
No problem at all. I use a steel telescopic pylon, 20 m long.

It supports two inverted V's: one for 40 m and one for 80 m. The wires are
kept 20 cm apart by 5/8" plastic tubing. The two inverted V's are fed in
parallel through a 1/4 balun at the end of a 50 ohms cable.

VSWR is almost 1/1 for 40 m. On 80 m the VSWR varies from 1/1 to 1,8/1.

At least 200 kHz of the 80 m band can be within 1,5/1. Of course, the
length of the elements determines witch part of the band that is.

That should have been "...which part of the band that is".
Sorry, my English stinks...

Metal mast for inverted V antenna support--will it work?
 

In article , somebody wrote:

What is the result of using a metal mast as the center support of an inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

If the metal mast is isolated from the inverted V feedpoint (e.g. you
use a center insulator) then there will be no direct current
conduction onto the mast. And, if the inverted V is symmetrical with
respect to the mast, there won't be much opportunity for current to be
induced onto the mast... it'll be exposed to equal-and-opposite RF
fields from the two sides of the inverted dipole and the fields will
cancel.

Since there will be little or no RF current flowing on the mast, there
will be little or no effect on the antenna's feedpoint impedance and
radiation pattern.

If you use a coax feedline, you could very easily have more RF flowing
on the outside of the coax than on the mast... due to direct
conduction at the feedpoint (if you don't use a balun) and due to
induction (if the feedline is not positioned symmetrically with
respect to the inverted V).

An inverted-V on a metal mast is perfectly capable of having a low
SWR, even without a tuner. I have a three-wire inverted-V "fan
dipole" (wires cut for 40/20/10-meter operation) mounted from the top
of a 25' metal mast, and the SWR is under 2:1 throughout the width of
all of these bands. The SWR depends far more on the angle of the V,
and the antenna's height above ground, than it does on the presence or
absence of the metal mast. Ditto for the antenna's pattern.

So, the answer is "Yes, it will work". As long as you don't connect
the V itself, or the coax feedline braid, to the top of the mast,
you're unlikely to be able to tell the difference between using a
metal mast and a completely nonconductive mast.

You should, of course, apply all relevant safety precautions with
respect to lightning, power lines, and so forth.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Metal mast for inverted V antenna support--will it work?
 

wrote in message ...
What is the result of using a metal mast as the center support of an
inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR

I had an inverted V for 80m supported from the top of my Rohn 25 tower

It was not directly supported by the tower but ratherit was suspended from
the end of a wooden yardarm.

Jimmie

Metal mast for inverted V antenna support--will it work?
 

"Philo" wrote in message
...
"Philo" wrote in message
...
No problem at all. I use a steel telescopic pylon, 20 m long.

It supports two inverted V's: one for 40 m and one for 80 m. The wires
are kept 20 cm apart by 5/8" plastic tubing. The two inverted V's are fed
in parallel through a 1/4 balun at the end of a 50 ohms cable.

VSWR is almost 1/1 for 40 m. On 80 m the VSWR varies from 1/1 to 1,8/1.

At least 200 kHz of the 80 m band can be within 1,5/1. Of course, the
length of the elements determines witch part of the band that is.

That should have been "...which part of the band that is".
Sorry, my English stinks...

Sorry, one more correction: the balun is a 1/1 type.

Metal mast for inverted V antenna support--will it work?
 

Sounds like mine (but it is only for SWLing)

On Jun 1, 2:08 pm, Irv Finkleman wrote:
wrote:
What is the result of using a metal mast as the center support of an inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR

There must be a million hams using their towers as the center support for
their vees. In theory the tower is at the electrical center and has little
or no effect. At least this is my theory!!! There are a few pundits who might
want to argue the point.

Irv VE6BP

Metal mast for inverted V antenna support--will it work?
 

On Jun 1, 2:43 pm, wrote:
What is the result of using a metal mast as the center support of an inverted V
antenna. Will it work and if so can resonable low SWR be obtained using a
tuner? Any advice appreciated.

TIR

I actually prefer a metal mast. In case of a lightning strike, the
mast
takes the bulk of the energy to ground, instead of my coax doing all
the
dirty work. A vertical on top of the mast can act as a lightning rod,
so all bets are off on those. But with my coax supported a foot or so
below the tip of the mast, feeding dipoles, I've taken strikes with no
coax
damage so far. There is some energy that runs the feedlines, but it's
fairly
small compared to the mast itself. It's enough to make an audible arc
sound
at my coax/bulkhead ground connection though. Thats with the
connectors
screwed in too.. I've never noticed any real RF coupling problems with
a
metal mast. You will see that with metal that parallels the antenna
legs
themselves. One of the worst coupling problems I ever saw as far as
tuning, was with a set of dipoles used next to a large mobile home.
All that metal surface gave us a fit. I had to try quite a few leg
locations/wire
lengths before I could get it tuned halfway decent. That was one of
the
rare cases I've seen where even the lowest band had problems.
MK

Metal mast for inverted V antenna support--will it work?
 

Metal mast for inverted V antenna support--will it work?
 

On Jun 3, 9:45 pm, John Smith I wrote:
wrote:

... screwed in too.. I've never noticed any real RF coupling problems with
a
metal mast. You will see that with metal that parallels the antenna
legs

...

Amazing we have not heard from the "EZNEC Experts" with plots of a metal
vs. non-metal support ...

JS


If the wires of the dipole are exactly perpendicular to the feedline,
and
no common mode currents, the plots should be the same.
The more sloping, the more coupling I would think, but even then,
it's rarely a problem.
MK

Metal mast for inverted V antenna support--will it work?
 

Metal mast for inverted V antenna support--will it work?
 

Owen Duffy wrote:
wrote in
oups.com:

On Jun 3, 9:45 pm, John Smith I wrote:
wrote:

... screwed in too.. I've never noticed any real RF coupling
problems with
a
metal mast. You will see that with metal that parallels the antenna
legs
...

Amazing we have not heard from the "EZNEC Experts" with plots of a
metal vs. non-metal support ...

JS

"John Smith" doesn't hear from this "EZNEC Expert" because I plonked him
a long time ago.

If the wires of the dipole are exactly perpendicular to the feedline,
and
no common mode currents, the plots should be the same.
The more sloping, the more coupling I would think, but even then,
it's rarely a problem.

Modelling the Inverted V without its support conductive mast is a little
like modelling it without a real model of its feedline, both ignore real
things that impact the antenna to some extent.

Owen

If you model the antenna as being perfectly symmetrical, then it makes
no difference whether you include the mast in the model or not -- the
result will be the same (assuming that the mast isn't in electrical
contact with the antenna). It might be interesting to purposefully make
the antenna model a bit non-symmetrical to see what effect the mast
would then have.

If you're not using an effective balun, adding a feedline to the model
will have an impact on the result (as it will on a real antenna) even if
the antenna is symmetrical, provided that you include the common mode
current path in the feedline model. This means modeling the feedline as
two wires, or by using the transmission line object plus a wire to
represent the outside of a coaxial cable. To be truly realistic, you
need to include the entire path to the Earth. This is seldom known, so
about the best you can do is to fiddle the length and orientation of
your feedline model to find the worst case and assume the real antenna
will have less common mode current than that.

Roy Lewallen, W7EL

Metal mast for inverted V antenna support--will it work?
 

Roy Lewallen wrote:

...
"John Smith" doesn't hear from this "EZNEC Expert" because I plonked him
a long time ago.
...
Roy Lewallen, W7EL

Roy:

You dropped out of being on the cutting edge long before I ever came along.

Don't even attempt to blame me for you devote religious beliefs in
established practices which are cloaked in "place-holder equations" ...
you only become ancient and unimportant when you quit adapting to change.

JS