How Handle Multiple Open Wire Lines?
 

I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to run
the feeline from each about 200 feet from the back pasture to the shack. I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably 150-200
feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough separation?
What other precautions do I need? Need they be twisted if they are not near
anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5"
wrote:

If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough separation?
What other precautions do I need? Need they be twisted if they are not near
anything other than the other feed lines?
Any help is appreciated.

Hi Greg,

Feed lines that are terminated in balanced loads are self isolating.
The balance of the load is with respect to earth and is discussed
under the heading of Common Modality. So your problems are load
defined, not line defined. Naturally there is a continuum of linkage
between lines even in this best of all possible worlds. That
continuum spans from considerable-to-miniscule and it is, as you have
guessed, dependant upon spacing.

What constitutes considerable may be miniscule for another and I will
leave that determination up to you, as you have offered no limits nor
quantitative concerns. If you need a rule of thumb, keep all lines at
least 10 times their own pair-spacing apart. That is, if a twin lead
has 1 inch spacing between the conductors, keep that twin lead 10
inches from a similar feedline.

There are no doubt authoritative reports to offer a justification for
this rule, or any other offered. I would expect this would come from
Laport's work (which several correspondents here have copies of).

73's
Richard Clark, KB7QHC

"greg knapp 5" wrote in message
...
I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to run
the feeline from each about 200 feet from the back pasture to the shack. I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably
150-200 feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough
separation? What other precautions do I need? Need they be twisted if
they are not near anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

Hi Greg:

I have just run a free space NEC 2 model of a pair of horizontally
positioned 6" wide, 600 ohm, transmission lines, vertically separated by
12". The model was run from 29 to 31 MHz. On 30 MHz , with both lines
terminated in 600 ohms the isolation was about 39 dB. With both lines
terminated in 6,000 ohms the isolation improved to 66 dB. The actual range
of impedances will be much higher, and complex, but it does give an idea of
the order of magnitude of the isolation. The calculation is based on the
ratio of the peak currents observed.

Hope this helps,

73,

Frank (VE6CB)

Why not just run one pair. Then split off at the end with the antennas.
The signal will take the path of least resistance, so the most likely
antenna for the job will be chosen automatically. The ones with high Z will
resist. Resistance is not futile.

My 2¢ (that "¢" key was tough to find)

"greg knapp 5" wrote in message
...
I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to run
the feeline from each about 200 feet from the back pasture to the shack. I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably
150-200
feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough
separation?
What other precautions do I need? Need they be twisted if they are not
near
anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

Thanks for the $.02 worth...it would be a good idea for me, but I will have
several antennas (of various types - dipoles, vee beams, etc.) capable of
being used for the same band, but at different angles from each other. I
hate to "share" my antennas and mess up the patterns I want to use. I
thought about switching way out back, but kind of hard to do A-B testing
when I have a 500 foot run to switch the antennas and get back to the shack!
I'm too old for that!
"Hal Rosser" wrote in message
...
Why not just run one pair. Then split off at the end with the antennas.
The signal will take the path of least resistance, so the most likely
antenna for the job will be chosen automatically. The ones with high Z
will
resist. Resistance is not futile.

My 2¢ (that "¢" key was tough to find)

"greg knapp 5" wrote in message
...
I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to
run
the feeline from each about 200 feet from the back pasture to the shack.
I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably
150-200
feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough
separation?
What other precautions do I need? Need they be twisted if they are not
near
anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

Thanks Frank for running the program and for the results. They give me a
good confirmation of what Riachard Clark showed me, I need to get more space
between these feeds than I was planning on. If I had 3 feeds, I guess I
ought to have a cross arm on my wood/PVC poles coming in and spread the
feeds by about two feet to minimize the interaction down to a miniscule
amount. I really do want to feed the antennas separately. Gee, I wonder
what W6AM used to do with his 10 or 12 rhombics fed with open wire all
coming into his home...

73,

Greg, N6GK


"Frank" wrote in message
news:xqNHe.177484$tt5.93925@edtnps90...
"greg knapp 5" wrote in message
...
I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to
run the feeline from each about 200 feet from the back pasture to the
shack. I don't want to walk out 200 feet and throw knife switches to
chose the antenna/feedline I want to feed, so I plan to run separate 600
ohm open feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably
150-200 feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough
separation? What other precautions do I need? Need they be twisted if
they are not near anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

Hi Greg:

I have just run a free space NEC 2 model of a pair of horizontally
positioned 6" wide, 600 ohm, transmission lines, vertically separated by
12". The model was run from 29 to 31 MHz. On 30 MHz , with both lines
terminated in 600 ohms the isolation was about 39 dB. With both lines
terminated in 6,000 ohms the isolation improved to 66 dB. The actual
range of impedances will be much higher, and complex, but it does give an
idea of the order of magnitude of the isolation. The calculation is based
on the ratio of the peak currents observed.

Hope this helps,

73,

Frank (VE6CB)

Wow, then if I had 6" spacing, it would have to be 5 feet from the nearest
other feed line! With the three lines I want to bring in, that is a cross
pole of 10 feet! Wow...I better consider using my old 450 ohm window ladder
line with about 1.x inch spacing so I can get down to a reasonable spread!

This is really opening my eyes up to the logistics of running this type of
feedline...low loss, but definitely more expense, bother, etc. than running
a bunch of coax lines! It almost makes me want to put up resonant antennas
(like parallel dipoles, fed with a balun and coax...so much easier!). I'm
going to have to think this through some more.

Thanks for the input,

Greg, N6GK

"Richard Clark" wrote in message
...
On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5"
wrote:

If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough
separation?
What other precautions do I need? Need they be twisted if they are not
near
anything other than the other feed lines?
Any help is appreciated.

Hi Greg,

Feed lines that are terminated in balanced loads are self isolating.
The balance of the load is with respect to earth and is discussed
under the heading of Common Modality. So your problems are load
defined, not line defined. Naturally there is a continuum of linkage
between lines even in this best of all possible worlds. That
continuum spans from considerable-to-miniscule and it is, as you have
guessed, dependant upon spacing.

What constitutes considerable may be miniscule for another and I will
leave that determination up to you, as you have offered no limits nor
quantitative concerns. If you need a rule of thumb, keep all lines at
least 10 times their own pair-spacing apart. That is, if a twin lead
has 1 inch spacing between the conductors, keep that twin lead 10
inches from a similar feedline.

There are no doubt authoritative reports to offer a justification for
this rule, or any other offered. I would expect this would come from
Laport's work (which several correspondents here have copies of).

73's
Richard Clark, KB7QHC

On Tue, 2 Aug 2005 21:41:42 -0700, "greg knapp 5"
wrote:

Wow, then if I had 6" spacing, it would have to be 5 feet from the nearest
other feed line!

Hi Greg,

Not really, you haven't told us how important the coupling factor is
yet.

73's
Richard Clark, KB7QHC

On Tue, 2 Aug 2005 21:41:42 -0700, "greg knapp 5"
wrote:

Wow, then if I had 6" spacing, it would have to be 5 feet from the nearest
other feed line! With the three lines I want to bring in, that is a cross
pole of 10 feet! Wow...I better consider using my old 450 ohm window ladder
line with about 1.x inch spacing so I can get down to a reasonable spread!

This is really opening my eyes up to the logistics of running this type of
feedline...low loss, but definitely more expense, bother, etc. than running
a bunch of coax lines! It almost makes me want to put up resonant antennas
(like parallel dipoles, fed with a balun and coax...so much easier!). I'm
going to have to think this through some more.


I worked in HF radio stations briefly a long time ago, and the
practice there was, IIRC, two wire lines of 3mm HDC with 200mm spacing
so they were around 600 ohms 'ish. There were also some 4 wire lines
with similar spacing (in a box config). These lines were strung out on
pole routes with separation about double the wire spacing. I can't
remember now if there were periodic polarity reversals. These were at
rx only or tx only facilities, so receiver de-sense was not an issue.
Do you need full duplex?

Clearly, the closer the lines the higher crosstalk (coupling from one
line to another), and presumably, twisted lines will have lower
crosstalk (think about the cat5 etc data cables).

Don't forget, that the antennas at the far end are coupled, and
achieving crosstalk of -100dB might not materially improve the
solution!

A pole route carrying a number of lines is a pretty serious project
(installation and maintenance). I would also look around at remote
switching solutions or multiband antennas to see if you can minimise
the number of lines you need to string.


Owen
--

Greg Knapp wrote:
"I need to feed many different antennas with open wire line and need to
run the feedline from each about 200 feet from the back pasture to the
shack."

This is similar to the problem facing commercial shortwave stations.
They usually have more distance and numbers of antennas and transmitters
to serve several target areas simultaneously.

The preferred solution is a feedline for each antenna. These separate
lines converge on the switching location near the plant. Each
transmitter is equipped with its own feedline too. These converge on the
switching location too.

In the "crossbar" switching arrangement, any transmitter may be
connected to any antenna. Very flexible and it works well.

When separate lines are too extravagant, a single line is switched at
both ends between some transmitters and some antennas. You need at least
as many lines as you have transmitters if all are going to operate at
once and not in parallel.

Most commercial stations have multiband radios but use narrowband
antenna systems. This requires many more antennas than transmitters to
serve many different targets in various bands required on the various
paths around the clock.

If you had only one direction or sense to serve, a single rhombic
connected by a single line to the transmitter might do a compromised
job. The rhombic will take a load at almost any frequency, but its
pattern changes with frequency so its coverage of a target won`t be
ideal at most frequencies.

If you don`t want to walk 200 feet to switch antennas, use relays
controlled from your shack. That`s what professionals do.

Best regards, Richard Harrison, KB5WZI

"greg knapp 5" wrote in message
...
Thanks Frank for running the program and for the results. They give me a
good confirmation of what Riachard Clark showed me, I need to get more
space between these feeds than I was planning on. If I had 3 feeds, I
guess I ought to have a cross arm on my wood/PVC poles coming in and
spread the feeds by about two feet to minimize the interaction down to a
miniscule amount. I really do want to feed the antennas separately. Gee,
I wonder what W6AM used to do with his 10 or 12 rhombics fed with open
wire all coming into his home...

73,

Greg, N6GK

No Problem Greg, glad to help. Just for interest I ran the program at
different spacings: at 6" the isolation is 27 dB, and at 2 ft 48 dB. Both
these measurements with 600 ohm terminations.

Balanced transmission lines radiate very little energy, but worst case
occurs at the higher frequency. For example the maximum radiated RF from a
terminated 600 ohm transmission line, at 30 MHz, is about -28 dBi.

I have seen pictures of W6AM's transmission lines, but can no longer find
them on the web. His antenna farm, as I understand, was purchased from a
commercial HF station. Interesting little article on W6AM in
http://www.mvarc.com/images/mvarcJULY05pp9.PDF

73,

Frank

I really can't answer how important the coupling factor is because I have
never dealt with this factor before.
I assume the only down side of too much coupling is that some small amount
of RF would then be coupled to the wrong antenna and radiated in some
pattern that is not necessarily desirable. So, as I understand it (I sure
could be wrong), if I was running a 1000 watts out, with coupling at -30 db,
1 watt would be coupled to the parallel line which would then be radiated by
the wrong antenna--which, if true, certainly doesn't seem significant. I am
not sure what is a significant level (i.e., significant distortion of net
radiation pattern) in dealing with two simultanteously feed antennas, but I
would think that if it is a ratio of the transmitted power, then 1000 vs 1
watt would seem to cause very minor distortion and would seem to be
acceptable. If my reasoning is OK, then I would think spacing of feedlines
would not need be too great, even if 5-inch spaced 600 ohm was used in place
of 1.x inch spaced 450 ohm line.
Any insight would be appreciated.
73,
Greg, N6GK

"Richard Clark" wrote in message
...
On Tue, 2 Aug 2005 21:41:42 -0700, "greg knapp 5"
wrote:

Wow, then if I had 6" spacing, it would have to be 5 feet from the nearest
other feed line!

Hi Greg,

Not really, you haven't told us how important the coupling factor is
yet.

73's
Richard Clark, KB7QHC

On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5"
wrote:

I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to run
the feeline from each about 200 feet from the back pasture to the shack. I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably 150-200
feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough separation?
What other precautions do I need? Need they be twisted if they are not near
anything other than the other feed lines?


I probably have more questions than answers.

1. Are the antennas to be operated independently? Is this a duplex or
diversity system?

2. Will the unused lines be terminated in the shack?

3. Are these multiband antennas with tuned feeders or could they just
as easily be coax-fed?

4. What do you consider to be detrimental interaction?


As others have suggested, there will be coupling between the antennas,
so feedline-to-feedline isolation will not necessarily be a figure of
merit.

If you consider the impedance change of a single pair of wires
operated over ground as a proxy for interaction, then with separation
by 3 or 4 times the wire spacing, you are probably okay for all but
the most critical situations.

One test would be to excite one line and measure the power in an
adjacent line, remembering that some (a lot?) of the coupling will be
antenna-to-antenna and will also be frequency dependent.

On Wed, 3 Aug 2005 09:18:38 -0700, "greg knapp 5"
wrote:

I really can't answer how important the coupling factor is because I have
never dealt with this factor before.

Hi Greg,

Frank has been carrying a lot of water for you in this regard. I
would point out (and he has stated as much) that his numbers are for a
load of 600 Ohms. Now, any mismatch will not have any impact on the
coupling, but the load's balance to earth will and Frank has done no
study of induced Common Mode currents. Given that there is a world of
possible imbalances possible, it is hard to know where to go from
there.

There is also a world of probable imbalances too. The antennas you
are feeding are far more likely the source of the problem of coupling
between lines than are the lines' proximity. However, proximity only
magnifies the problem. Still and all, even the worst imbalance is
unlikely to pose significant issues. It might be problematic for a
VOA feed of 500KW with leakage of their European service into their
African service, but you are not in that class (and they probably now
how to keep their antennas balanced too).

73's
Richard Clark, KB7QHC

As an alternative to running the feelines of my proposed multiple antennas
(dipoles, vee beam, etc.) in parallel 250 feet from the back pasture, I've
come up with an idea for remotely switching the feedlines. Here's the idea
for handling multiple open wire lines...switch them remotely using only the
center of the coax fittings on a remote coax antenna switch (the type that
switch 4, 6, or 8 coax antennas).
This might be accomplished at least three ways:
1) just hook one side of all the feedlines together and switch the other one
by plugging them (using banana plugs or similar) into the center conductor
of the coax fittings
2) have two coax switches, so that both sides of the feedlines are kept
separate and switched by throwing two coax switches in synchronization.
Which of these would work best, or neither? Would the impedence bump cause
any significant problem? Has someone actually tried this? What about
proximity between the feedlines gathered around the switches...would that
cause significant problems at the legal limit (I notice Cecil's switch
design has them pretty close to each other...but not this close)?
3) give up and go back to parallel lines until they reach the shack and
switch them with banana plugs.
One kind person responded privately with a picture of W6AM's home showing
the independent openwire feed lines going into the house about 8 different
places spaced about 2.5 feet apart, obviously to either dedicated
tuners/rigs or some horrendous switching network that was knife thrown. I
really don't want to do that, if I can avoid it.
This all is getting so complex, to presere my sanity and pocket book I might
just be forced to go back to resonant antennas on all bands so I can use
coax without undo loss! Hi!
73,
Greg, N6GK

On Wed, 3 Aug 2005 16:56:25 -0700, "greg knapp 5"
wrote:
[snip]


This all is getting so complex, to presere my sanity and pocket book I might
just be forced to go back to resonant antennas on all bands so I can use
coax without undo loss! Hi!

There you go. Run a piece of Heliax out there and use one of your
coax relays as it was intended.

Even at SWR = 3:1 @ 28 MHz, 200' of 1/2" Heliax will lose only about a
dB. Use 7/8" line and you could stand 5:1 for less than a dB.

On Wed, 3 Aug 2005 16:56:25 -0700, "greg knapp 5"
wrote:

This may or may not help, but FWIW, MFJ makes an (indoor) antenna
switch that handles six balanced feedlines. May help if you run
several lines to your house...

bob
k5qwg

In answer to your questions below, I would expect to only use one antenna at
a time, switching between them when wanting to use a different antenna or
directivity.

I would expect to use banana plugs to short the unused antennas to ground
just outside the shack, hooking up only the one to be used. I don't like the
idea of having an ungrounded feedline...lightning/static discharge hurts!

The open wire/coax question is a good one. Some of my antennas will be open
wire (vee beam, center fed 80 meter dipole for 80-10 meters), but others,
another dipole for 80 at 90 degrees and 150 foot separation is resonant and
fed with coax, while I have two verticals fed with coax, plan to experiment
with wire LPDAs, etc. So I am trying to think this thing through now,
especially in buying a tuner, as I can't afford both a Balanced tuner (ala
Palstar BT1500BAL) and an Unbalanced L tuner (TenTec 238B).

I feel like I have gotten a college education on balanced feeds and it's
caused me to reevaluate if that is really the easiest way to go. I started
out thinking about using just ONE antenna (80 or 160 dipole center fed with
600 ohm line) up about 75 feet on a 45 foot light weight tower and 30 feet
of mast above that. I liked the gain on the higher (20-10 meter) bands, but
the patterns wouldn't all be in the directions I want given the orientation
I have available for the antenna. So I started thinking about TWO such
antennas, with the second one on a 40 foot pushup mast. The I thought about
adding the Vee Beam I used to have long ago...really worked well on
20-10...definitely a good antenna with the 2 acres I have. And so forth. As
most of these antennas would be for multiband use, a balanced tuner would be
ideal, but then I had the questions of how to route the feedlines to keep
them out of the other antenna fields and away from each other. Having
always used coax, this is starting to seem like a nightmare. I almost think
the best is to do as one gent suggested, just put in an 80 meter or 160
meter loop, feed it with 450 or 600 ohm, and all it a day.

As I am no longer an avid DXer (used to have stacked beams for 10 through
40), but enjoy chatting on all modes on all bands, with reasonably good
signals, I think perhaps at the end of the day maybe the two 80 meter
dipoles at right angles (roughly forming an L from a top view) but about 100
feet apart, with one at 75 feet and the other at 40 feet might be the
solution, fed with 600 ohm to EITHER a balun-coax-L tuner or direct to a
balanced tuner. Good enough is good enough. Of course, I just know I'll
throw back up the 300 foot Vee Beam for 20 through 10 at some point, health
permitting.

Oh, so many choices and dreams! I think I am going to start small, probably
the dipole at 40 feet 350 feet away. That will satisfy until I get the tower
refurbished and up in September. The reason I have had so many questions is
because I am trying to foresee what my needs will be a year from now...I
don't want to say, gee, I should have thought of that!

73,

Greg, N6GK



I probably have more questions than answers.

1. Are the antennas to be operated independently? Is this a duplex or
diversity system?

2. Will the unused lines be terminated in the shack?

3. Are these multiband antennas with tuned feeders or could they just
as easily be coax-fed?

4. What do you consider to be detrimental interaction?


As others have suggested, there will be coupling between the antennas,
so feedline-to-feedline isolation will not necessarily be a figure of
merit.

If you consider the impedance change of a single pair of wires
operated over ground as a proxy for interaction, then with separation
by 3 or 4 times the wire spacing, you are probably okay for all but
the most critical situations.

One test would be to excite one line and measure the power in an
adjacent line, remembering that some (a lot?) of the coupling will be
antenna-to-antenna and will also be frequency dependent.

Here is a commercial implementation of MF / HF transmission lines.
(They are not telephone lines.)

http://members-central.optushome.com...3ase/feed2.jpg

http://members-central.optushome.com.au/vk3ase/feed.jpg

Owen

On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5"
wrote:

I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to run
the feeline from each about 200 feet from the back pasture to the shack. I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably 150-200
feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough separation?
What other precautions do I need? Need they be twisted if they are not near
anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

--