Two dipoles on one coax
 

What is the best way to use one feed line for more than one dipole?
Or, is it better to use a coax switch in the shack?

Thanks, Ron

"rhymer" wrote
What is the best way to use one feed line for more than one dipole?
Or, is it better to use a coax switch in the shack?

Ron, your subject line "Two dipoles on one coax" implies the typical antenna
selector switch that leaves no question (of course you can do that). But the
message body asks about one feedline for more than one dipole as opposed to
the antenna selector. The two choices are so unequal that a comparison is
not possible.

Someone may explain here that they have connected more than one antenna with
a single feedline, but it flies in the face of proper operating procedure.
Most operators however do use antenna selector switches to provide more than
one antenna choice to a given receiver or transmitter. The individual
antennas always have their own individual feedline in those cases.

Best regards,

Jack Painter
Virginia Beach

"rhymer" wrote in message
...
What is the best way to use one feed line for more than one dipole?
Or, is it better to use a coax switch in the shack?

Thanks, Ron

Ron,

Connecting two *dipoles* to the same feedline works just fine. Just tie them
directly to the same balun. There will be two kinds of interaction: first,
the two are electrically in parallel, and second, the wires themselves could
have mutual coupling. The first seems to not really be a problem, and the
second is minimized if there is separation between the two dipoles. For best
results, put them at right angles to each other; if that is not possible,
have at least 15 - 30 degrees separation, either vertical or horizontal. For
instance, you could have a dipole supported at the ends, with an inverted V
hanging below it.

The most interesting case is for antennas at 75 and 80 meters. You get 2:1
SWR from 3.5 to 4 MHz in a virtually non directional antenna (if the two
dipoles are at 90 degrees).

I presently have a 40 m inverted V hanging below an 17 m dipole. (The trees
are too close to do it the other way). The 40 meter is also out of plane to
miss the trees. Works great.

Since you have to trim the lengths slightly (lowest frequency first), it is
simplest to run EZNEC or some other simulation first.

Tam/WB2TT

Jack Painter wrote:
Someone may explain here that they have connected more than one antenna with
a single feedline, but it flies in the face of proper operating procedure.

Except, of course, for paralleled dipoles where only one of
them is resonant (low feedpoint impedance) on any one frequency.
Perhaps that is what he is talking about.
--
73, Cecil http://www.qsl.net/w5dxp

Ron,
It's mainly a matter of convenience, or maybe you only
have enough feed line for one feed line.
Depending on 'how' you use the connected-together antennas,
only for use on the intended bands they are cut for, or as
multiband antennas, it might be simpler to use seperate feed
lines for each.
As for the 'best' way of connecting two or more antennas
for use on a single feed line, attach them to whatever you're
using for a center insulator, the second antenna just like the
first one. There are a number of 'mechanical' ways of doing
that and the 'best' is which ever is easiest for you (or how
ever you know how to do it). As you'd expect, the connections
should be strong enough, light weight enough, and sort of
'pretty' enough to satisfy the antenna's requirements and any
'significant other' that's around (wife, neighbors, landlord,
etc.).
Using seperate feed lines and an antenna switch makes the
process of tuning the antennas a bit 'easier', probably won't
take as long. Which ~may~ be the only difference depending on
how/where you erect the antennas.
Of course, using antennas that are high, widely seperated,
and
fed seperately is always nice! If you have the room, the
required
feed lines, a switch, the time to do it, and so on (I wish!)...
'Doc

"Cecil Moore" wrote in message
...
Jack Painter wrote:
Someone may explain here that they have connected more than one antenna
with
a single feedline, but it flies in the face of proper operating
procedure.

Except, of course, for paralleled dipoles where only one of
them is resonant (low feedpoint impedance) on any one frequency.
Perhaps that is what he is talking about.

Thanks Cecil. I meant to say "normal" operating procedure. I knew you guys
had examples of why you would do otherwise, LOL.

Best,

Jack Painter
Virginia Beach, Va

On Fri, 21 May 2004 09:21:44 -0400, "Jack Painter"
wrote:

"rhymer" wrote
What is the best way to use one feed line for more than one dipole?
Or, is it better to use a coax switch in the shack?

Ron, your subject line "Two dipoles on one coax" implies the typical antenna
selector switch that leaves no question (of course you can do that). But the
message body asks about one feedline for more than one dipole as opposed to
the antenna selector. The two choices are so unequal that a comparison is
not possible.

I have no idea what you mean by "typical antenna selector switch".

Someone may explain here that they have connected more than one antenna with
a single feedline, but it flies in the face of proper operating procedure.
Most operators however do use antenna selector switches to provide more than
one antenna choice to a given receiver or transmitter. The individual
antennas always have their own individual feedline in those cases.

Yes, I was referring to more than one dipole on a single feed line (in
my case two dipoles 40 and 15).

Thanks, Ron

Best regards,

Jack Painter
Virginia Beach

What u r describing is a "multi dipole".

I have used combo 75 and 160 fed with same RG58 and had no problems.

73 de Jack, K9CUN

On Fri, 21 May 2004 10:22:20 -0400, "Tam/WB2TT"
wrote:


"rhymer" wrote in message
.. .
What is the best way to use one feed line for more than one dipole?
Or, is it better to use a coax switch in the shack?

Thanks, Ron

Ron,

Connecting two *dipoles* to the same feedline works just fine. Just tie them
directly to the same balun. There will be two kinds of interaction: first,
the two are electrically in parallel, and second, the wires themselves could
have mutual coupling. The first seems to not really be a problem, and the
second is minimized if there is separation between the two dipoles. For best
results, put them at right angles to each other; if that is not possible,
have at least 15 - 30 degrees separation, either vertical or horizontal. For
instance, you could have a dipole supported at the ends, with an inverted V
hanging below it.

That's what I wanted to hear, that it can be done without using
anything special. It sure would beat switching them at the xmitter. I
have always used separate feed lines and recently I read where someone
had 4 dipoles on the same feed line.


The most interesting case is for antennas at 75 and 80 meters. You get 2:1
SWR from 3.5 to 4 MHz in a virtually non directional antenna (if the two
dipoles are at 90 degrees).

That sounds really cool.

I presently have a 40 m inverted V hanging below an 17 m dipole. (The trees
are too close to do it the other way). The 40 meter is also out of plane to
miss the trees. Works great.

Is the 40m at a right angle to the 17m, or is the V separation
adequate?

Since you have to trim the lengths slightly (lowest frequency first), it is
simplest to run EZNEC or some other simulation first.

Tam/WB2TT

Thanks muchly for that,

Ron, W1WBV

On Fri, 21 May 2004 10:53:23 -0500, 'Doc wrote:

Ron,
It's mainly a matter of convenience, or maybe you only
have enough feed line for one feed line.
Depending on 'how' you use the connected-together antennas,
only for use on the intended bands they are cut for, or as
multiband antennas, it might be simpler to use seperate feed
lines for each.
As for the 'best' way of connecting two or more antennas
for use on a single feed line, attach them to whatever you're
using for a center insulator, the second antenna just like the
first one. There are a number of 'mechanical' ways of doing
that and the 'best' is which ever is easiest for you (or how
ever you know how to do it). As you'd expect, the connections
should be strong enough, light weight enough, and sort of
'pretty' enough to satisfy the antenna's requirements and any
'significant other' that's around (wife, neighbors, landlord,
etc.).

I own the house, we have a 2 acre minimum and my XYL is a ham . . .
KB1FZM :-)

Using seperate feed lines and an antenna switch makes the
process of tuning the antennas a bit 'easier', probably won't
take as long. Which ~may~ be the only difference depending on
how/where you erect the antennas.
Of course, using antennas that are high, widely seperated,
and
fed seperately is always nice! If you have the room, the
required
feed lines, a switch, the time to do it, and so on (I wish!)...
'Doc

I have the space but my lot is heavily treed. That is the way we like
it, so I would rather not cut any trees. The antennas will cross each
other, so it will benefit me if I can tie them together at the center.
My 40 m antenna didn't survive the winter.

Thank, Ron W1WBV