"'Doc" wrote in message ...


Dave,
There is a big difference between the current flowing on
the inside of the shield of coax and any current flowing on
the outside of the shield. The current flowing on the inside
of the coax shield is the same current that flows in the
center conductor (not the same polarity/phase). Ideally, there
will be no current flowing on the outside of the coax shield,
but you very seldom ever run across the 'ideal' situation. The
current flowing on the outside of the shield is what makes the
feed line radiate.
'Doc

exactly.

On Mon, 15 Sep 2003 14:15:05 -0500, "Dave VanHorn"
wrote:


So I can feed my Ground plane or quad with a balun, then its a dipole?

no, it's not. be careful, you're making my case.

No, you said:

in order to be a dipole, it has to be fed with two signals, 180
degrees out of phase, and equal ampliude.

Be careful, your hurting your case, so by what you posted any antenna
can be a dipole if it meets the requirement of being fed two 180 out
of phase signals of equal amplitude?


a proper dipole is resonant, given a balanced feed, and therefore does not
put significant signal onto the coax shield. /or it's fed with ladder line,
from a balun in your tuner/



So, we all use improper dipoles, big deal. They are still dipoles,
spend some time building and using them, in real on the air tests, not
in your lab. Balun manufacturers won't make claims of significant
signal gains.

I'll keep building my dipoles without a balun, fed with coax, and be
very happy with how well they work.

Thanks everybody, after I sort out all this info I will have a PHD in Dipole
Antennas


Regards,
br549


"nocents" wrote in message
om...
Sorry if I am redundant, this is the fist time on this group, I am using
Central Florida Road Runner and their NG retention is about 48 hours, so I
can't search the old posts.

I bought a RS TRC-458 Navaho base station at a garage sale this weekend
for
ten dollars and I have a twenty foot mast and I would like to build my own
antenna, to save $$$.

The pattern needs to be at least 180 degrees as I live on the coast of
Florida. I plan to run barefoot (till I can buy some power) so I need some
efficiency.

Thanks,

BR549

In , "Dave VanHorn"
wrote:


So I can feed my Ground plane or quad with a balun, then its a dipole?

no, it's not. be careful, you're making my case.

for a pair of quarter-wavelength wires to act as a dipole, several things
must be true.
physical arraingement, and feed are both important. your broken dipole is
somewhere between a real dipole, and the ground plane. basically, a
monopole, with a counterpoise.

Wrong. The only requirements for a dipole are that it has max current in the
center, and has two ends with max voltage but opposite polarity (hence the
origination of the term 'DI-POLE'). The only way to do this is to locate the
ends in polar opposition, and to use a frequency on which it is resonant (any
multiple of 1/2 wavelength). As I said in another post, a dipole can be nothing
more than a single wire fed at the center with coax and a gamma match. A dipole
is therefore not necessarily a doublet, nor does it necessarily need to be fed
from a balanced line or balun. In fact, a 1/4 wave vertical groundplane antenna
is really a dipole -- the groundplane (or 'counterpoise') functions as one pole
of a two pole (dipole) antenna. It meets all the criteria: the two ends are in
polar opposition, it is resonant on a specific frequency (the length of the 1/4
wave vertical being calculated as half the length of a dipole), has max current
at the center (the base of the vertical), and max voltage on the ends (the top
of the vertical).

And BTW, a 'doublet' only means the antenna has two elements. That's all.

if you significantly bend the wires, or re-arrainge them physically, then it
is no longer a dipole.

if we remove three radials from your ground plane, /i'm assuming it's fed
with unbalanced line directly, as it should be/ and straighten out the
remaining radial relative to the driven element, then we have your broken
dipole again.

there's another class of antenna, called a bicone, that has significantly
different charachteristics, but is conceptually very close to the dipole.

That's probably why it's also called a biconical dipole.

it's got broader bandwidth, and is commonly used in part 15 testing for that
reason. the discone is another very close relation, somewhere between the
bicone, ground plane, and a feedhorn.

The discone is a non-resonant antenna that works nothing like a dipole.

this stuff does matter. when you make changes, they have effects, even if
your particular arrangement is too sloppy to notice them. when you make a
change that should have an effect, and it dosent, this is telling you that
you have other problems.

do you not see the difference between a driven, and a passive element

You think the end thats fed with the shield of the coax is passive?
Come on over and grab the end of my dipole, (fed with coax and no
balun), when I have 1Kw running to it. You will change your mind
about it being passive.

no, i won't. where did you get the idea that passive elements wouldn't have
current flowing in them. and where pray tell, is that current coming from

grab the director on a beam, and see what you get. that's a simple wire
sitting in space, with no connection to the coax at all.. is it a passive
element, absolutely.. has it got rf current flowing in it, you'd better
believe it.

your two wires fed in the middle with coax, are not a dipole.
the best name i can give it, is a monopole with counterpoise.

It's the same thing.

throw it into mininec, and see if you get the same results as a properly
constructed dipole.

By that definition, any dipole that doesn't behave like an ideal dipole can't be
a dipole, including any dipole that doesn't exist in free space. Since there is
no place on earth that is equivalent to free space, it is therefore -impossible-
to build a "properly constructed" dipole!

that's freeware, a little limited, but it can do simple antennas like
dipoles with no problems.

you've also got a lot of rf current on your shield, which is making the
shield an active part of the antenna. you didn't think that this current on
your non-driven element magically stopped at the connector, did you.. why
would it stop there.. there is one possibility, that your feedline is an odd
number of quarter wavelengths long, so that this pont is high impedance. but
that only works at particular frequencies.

That doesn't work at all. The point where the coax shield meets the antenna is a
point of low impedance, and if the coax is an odd number of wavelengths long
with the radio end RF grounded, the result is an detuned mess. And if the radio
end -isn't- RF grounded, that's what puts RF in the shack and burns your lips.
But that doesn't mean the antenna isn't a dipole -- it's just a dipole that has
been poorly implemented.

in this case, it's still not a
dipole, /half the antenna isn't driven/ but it will work better than an
identical antenna with feedline an even number of quarter wavelengths long.

You will notice very little, or more likey no difference between a
dipole fed with or without a Balun.

like i said, errors in one area can obscure results in another area.

almost any damn thing will radiate and be tuneable.
a quick look at the antenna wall in the local truck stop will tell you that.

a proper dipole is resonant, given a balanced feed,

Wrong again. A dipole is resonant with or without the feed line.

and therefore does not
put significant signal onto the coax shield. /or it's fed with ladder line,
from a balun in your tuner/

Hit the books and look up "gamma match". Look up "dipole" while you are at it.





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Dave,
And the idea of 'half' of a dipole as being a 'passive'
element. In which half of a signal's cycle is the shield
side of the dipole passive? The 'positive' or 'negative'
half cycle? And since current is still moving in the
'passive' half of the antenna, it's also still being
radiated. How does that fit in with your 'passive' element
description? If it radiates, it ain't 'passive'.
I can follow your thinking, but your thinking will lead
you into making very confusing statements as you've done.
Why not stick to the 'standard' or common way of describing
what you mean? It'll save a lot of confusion and bandwidth.
'Doc

Have you ever built and used a dipole with a balun, without a balun
and used them on CB or the HF bands?

absolutely.

i haven't done base station cb work since the late 70's but physics hasn't
changed.
these days, i'm up on 40-10, and 6-902.
many dipoles, over the years. both ways.

How does that fit in with your 'passive' element
description? If it radiates, it ain't 'passive'.

the passive elements on a yagi have current flow in them, and they are
indeed passive elements.
passive dosen't mean 'no current flow' in this context, it means not driven
from the feedline.

I can follow your thinking, but your thinking will lead
you into making very confusing statements as you've done.
Why not stick to the 'standard' or common way of describing
what you mean? It'll save a lot of confusion and bandwidth.
'Doc

i didn't coin the term 'passive element'

Be careful, your hurting your case, so by what you posted any antenna
can be a dipole if it meets the requirement of being fed two 180 out
of phase signals of equal amplitude?

no, there are several conditions, balanced feed is only one of them.


So, we all use improper dipoles, big deal. They are still dipoles,
spend some time building and using them, in real on the air tests, not
in your lab. Balun manufacturers won't make claims of significant
signal gains.

a balun isn't a gain device. neither is wire, but combine them, and you get
a gain device, which is a system called an antenna.

I'll keep building my dipoles without a balun, fed with coax, and be
very happy with how well they work.

ok

On Tue, 16 Sep 2003 07:14:30 -0500, "Dave VanHorn"
wrote:

a balun isn't a gain device. neither is wire, but combine them, and you get
a gain device, which is a system called an antenna.

Really? How much gain? If I have a dipole fed without a balun, how
much gain will I get when I add a balun to it?

Does it have to be a gain device to be able to call it an antenna
system?

You have already been given the definition of a dipole by several
people. If you prefer to call it something else, call it what ever
you want . It shouldn't take you more than a couple of weeks to
change all the text books and technical references to your definition
of a dipole.

If I have any questions on the correct way to build a dipole, I'll ask
Frank or Doc. They understand how to build them.

Dave,
----snipped--------
passive dosen't mean 'no current flow' in this context, it means not driven
from the feedline.


And the 'passive' element of a dipole antenna ~isn't~ fed
from the feed line? Confusing'er and confusing'er. I thought
both 'halves' of a dipole were fed by the feed line, certainly
every one that I've made, or seen have been.

----snipped---------

i didn't coin the term 'passive element'

No, I'm aware of that. But are you the one who 'minted' the
"two signal" way of looking at a single signal? Like some other
types of esoteric thinking you have to be very careful where
they
are applied, and how. If you aren't careful, they deteriorate
into nonsense as has happened here. If how you think about a
dipole antenna helps you with what you're doing, then fine, have
at it. That doesn't make it 'correct' or the 'right' way of
doing
things, though, and it is very confusing to someone who isn't
familiar with that particular 'theory' of operation. If you
want to
call a dipole by another name, that's fine too. But it don't
make
it so. Aunt Martha wasn't born with wheels, so she really isn't
a Buick... no matter what she thinks.
'Doc