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Question about Full Wave loop



 
 
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  #1  
Old March 19th 04, 05:48 PM
HaveHFWillTravel
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Default Question about Full Wave loop

I am buying a house with 1.25 wooded acres. I want to put a loop
skywire for 160-80 meters. I am hoping to get it up 60 feet in the
trees. Anyways I noticed on the radiation graphic that a major lobe of
the antenna is 90 degrees from horizontal. Question is if I slope the
antenna, will it lower the 90 degree lobe to to something that sends
rf out instead of straight up and should it lower the take-off angle
assuming the soil conductivity is good. KG4CYB
  #2  
Old March 19th 04, 09:49 PM
'Doc
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'CYB',
A major lobe of a horizontal loop is 'straight up', but that
doesn't
mean that all the RF is going that way by any means, and a high
radiation
angle isn't always 'bad'. 'Tilting' a horizontal loop does
change the
direction of the radiation pattern, but because of all the
things that
affect the radiation pattern, where it actually 'goes' is very
hard (if
not impossible) to predict. Best advice? Try it and see what
happens.
I'm using a horizontal 80 meter loop on a city lot. I've had
no more
than the 'usual' problems working a WAS (several times), and all
the DX
I cared to 'mess' with. A loop has several good and bad
characteristics,
just like any other antenna, and what works well 'here' may not
work well
'there' (just like any other antenna). I just wish the thing
was at 60
feet instead of 20 (LOL)! A characteristic that I like is that
when fed
with ladder line through a tuner, (I know Cecil, but I've got
the tuner),
it works almost all bands, sort of a problem loading on 15
meters, but I
don't use 15 anyway.
Good luck...
'Doc
  #3  
Old April 10th 04, 04:43 AM
zeno
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Posts: n/a
Default

I was contemplating putting up a full wave 160m sky wire horizontal
loop. It will be kind of a square (more trapazoid actually). I was
hoping to use it multi-band. I am hoping to get the corners up on
metal masts up at least 50 feet.

1. Is it worth the extra trouble to get ladder line and feed into
the shack (house) (as opposed to coax)? I will have pulleys so I
could try one and then the other.

2. What length should I cut it for? I am new, don't particular know
what frequency I might be on. I had heard that the 160m loop
(approx. 540' or so) could be good as a multi-band. What exact
length should I aim for, or is it even critical? 1005/?

3. If I use ladder line, I would have to use a balun in the shack
to convert to coax a short run to go to my Kenwood Tuner (which has
160m), on other bands I would use a small Johnson Matchbox which
lacks 160m and eliminate this balun. I am envisioning some kind of
old- fashioned DPDT knife switch, I guess.

4. Actually, as a newbie, I have a nothing but more questions, like
how best to override the built in relay in the Johnson Matchbox
etc. I am gradually figuring this stuff out and hope to find some
locals also.

5. If the ladder line proves to be problematic (there are some
nearby tv cables, phone lines maybe 5-6' away at one closest point)
would a coax feed to this 160m loop still be multi-band? I am not
finding a consistent answer to this question anywhere online.

6. Glad to have found this board, since I am lately obsessed with
putting in an antenna farm on the real estate (very big rural back
yard).

7. I welcome any additions and/or corrections to my thinking so far
on this loop project. At this point, I am just scrounging together
the masts and pulleys etc. deciding whether to use rope or wire
guys...

-Bill


'Doc wrote:

'CYB',
A major lobe of a horizontal loop is 'straight up', but that
doesn't
mean that all the RF is going that way by any means, and a high
radiation
angle isn't always 'bad'. 'Tilting' a horizontal loop does
change the
direction of the radiation pattern, but because of all the
things that
affect the radiation pattern, where it actually 'goes' is very
hard (if
not impossible) to predict. Best advice? Try it and see what
happens.
I'm using a horizontal 80 meter loop on a city lot. I've had
no more
than the 'usual' problems working a WAS (several times), and all
the DX
I cared to 'mess' with. A loop has several good and bad
characteristics,
just like any other antenna, and what works well 'here' may not
work well
'there' (just like any other antenna). I just wish the thing
was at 60
feet instead of 20 (LOL)! A characteristic that I like is that
when fed
with ladder line through a tuner, (I know Cecil, but I've got
the tuner),
it works almost all bands, sort of a problem loading on 15
meters, but I
don't use 15 anyway.
Good luck...
'Doc


  #4  
Old April 10th 04, 06:16 AM
Reg Edwards
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Posts: n/a
Default

Zeno, In answer to some of your questions -

For multi-band working, ladder-line or preferably open wire line is almost
essential.

Overall antenna length is very non-critical. When using a tuner you can be
many feet adrift from the theoretical calculation without any degredation in
performance. A change in length affects only the radiation pattern which
for practical purposes can be considered omni-directional anyway.

For multiband operation be prepared to make relatively small changes in
length of feedline as part of tuner operation.

Use a simple choke balun at the transmitter end with a balanced feedline.
Make no attempt with a voltage-ratio balun to match feeder input impedance
to 50 ohms. Leave that entirely to the tuner.

A choke balun for 160 meters consists of a 1.5" to 2" diameter ferrite ring
wound with 8 to 12 turns of 18-gauge flexible speaker cable, or similar.

A coax feedline means lossy operation on other than the fundamental
frequency.

A balanced feedline near to phone or power cables will cause no trouble
unless nearly touching over a long distance.
---
Reg, G4FGQ


  #5  
Old April 10th 04, 01:34 PM
T.E.O
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Posts: n/a
Default

One man's opinion:
Get it as high as you can, use balanced line & the Matchbox.

Coax has much more loss @ SWR 1:1 than balanced line. And you will have
high SWR (on the feedline) on some bands. The plastic "window" 450 ohm
ladder line is OK but acts funny when wet (SWR swings). All that plastic
insulation is the culprit. Moisture on the plastic causes oscillations that
wreak havoc on SWR. Best to make-up your own balanced line with as few
spacers between the wires as possible.

To disable the Matchbox relay, use a small bit of matchbook cover or old
credit card between the relay contacts. That's what I did with mine & it's
worked great for years. Very easy to revert back to the relay if you ever go
to separate transmitter/receiver.

I stay away from baluns when I intend multi-band use. They don't act the
same at all frequencies. The Matchbox has no balun, the transmitter output
is coupled to the transmission line via a link. Also, you can extend the
range of the Matchbox (to cover 160). See a "how to" article in Electic
Radio Magazine -March, 2001 issue# 142, page 10. Back issues are available
for $3.75 he http://www.ermag.com/.







1. Is it worth the extra trouble to get ladder line and feed into
the shack (house) (as opposed to coax)? I will have pulleys so I
could try one and then the other.

2. What length should I cut it for? I am new, don't particular know
what frequency I might be on. I had heard that the 160m loop
(approx. 540' or so) could be good as a multi-band. What exact
length should I aim for, or is it even critical? 1005/?

3. If I use ladder line, I would have to use a balun in the shack
to convert to coax a short run to go to my Kenwood Tuner (which has
160m), on other bands I would use a small Johnson Matchbox which
lacks 160m and eliminate this balun. I am envisioning some kind of
old- fashioned DPDT knife switch, I guess.

4. Actually, as a newbie, I have a nothing but more questions, like
how best to override the built in relay in the Johnson Matchbox
etc. I am gradually figuring this stuff out and hope to find some
locals also.



  #6  
Old April 10th 04, 05:58 PM
zeno
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Posts: n/a
Default

Thanks for response Reg, here are a couple of follow up questions:

Reg Edwards wrote:

Zeno, In answer to some of your questions -

For multi-band working, ladder-line or preferably open wire line is almost
essential.

Overall antenna length is very non-critical. When using a tuner you can be
many feet adrift from the theoretical calculation without any degredation in
performance. A change in length affects only the radiation pattern which
for practical purposes can be considered omni-directional anyway.

For multiband operation be prepared to make relatively small changes in
length of feedline as part of tuner operation.


Are you saying that every time you would switch bands or frequencies, one might
have to change length of feedline? I am trying to picture that, is there some
convenient solution to this process?



Use a simple choke balun at the transmitter end with a balanced feedline.
Make no attempt with a voltage-ratio balun to match feeder input impedance
to 50 ohms. Leave that entirely to the tuner.

A choke balun for 160 meters consists of a 1.5" to 2" diameter ferrite ring
wound with 8 to 12 turns of 18-gauge flexible speaker cable, or similar.


Just to make sure we are on the same page he are you saying to use this
choke balun just for operation on 160m if I want to use my Kenwood tuner? I am
assuming that when using the Johnson Matchbox for the bands it was designed for
I would connect the feed line directly to the Matchbox terminals, and that
feedline would connect directly to the antenna (no baluns, no chokes, or
anything).



A coax feedline means lossy operation on other than the fundamental
frequency.

A balanced feedline near to phone or power cables will cause no trouble
unless nearly touching over a long distance.
---
Reg, G4FGQ


  #7  
Old April 10th 04, 06:07 PM
zeno
Guest
 
Posts: n/a
Default

T.E.O. thanks for the response and good info: here are a couple of follow up
questions:

"T.E.O" wrote:

One man's opinion:
Get it as high as you can, use balanced line & the Matchbox.

Coax has much more loss @ SWR 1:1 than balanced line. And you will have
high SWR (on the feedline) on some bands. The plastic "window" 450 ohm
ladder line is OK but acts funny when wet (SWR swings). All that plastic
insulation is the culprit. Moisture on the plastic causes oscillations that
wreak havoc on SWR. Best to make-up your own balanced line with as few
spacers between the wires as possible.


Do you have any pointers or good recipes for making my own balanced line?
materials, spacing, wire size, insulated vs. bare, etc. never done this before.
Also I will have to go through approx. 1+" of wood at the peak of my house, and
then again about 1" of wood to come down through the old farmhouse ceiling
directly to the station. This balanced line will be travelling about 12 feet or
so through my attic and fortunately there is not metal or wiring in that area
to speak of.


To disable the Matchbox relay, use a small bit of matchbook cover or old
credit card between the relay contacts. That's what I did with mine & it's
worked great for years. Very easy to revert back to the relay if you ever go
to separate transmitter/receiver.


Great solution....why didn't I think of that?


I stay away from baluns when I intend multi-band use. They don't act the
same at all frequencies. The Matchbox has no balun, the transmitter output
is coupled to the transmission line via a link. Also, you can extend the
range of the Matchbox (to cover 160). See a "how to" article in Electic
Radio Magazine -March, 2001 issue# 142, page 10. Back issues are available
for $3.75 he http://www.ermag.com/.


thanks for the link, I will look that up.

Zeno (aka Bill -- middle name, and better cw rhythm.....)




1. Is it worth the extra trouble to get ladder line and feed into
the shack (house) (as opposed to coax)? I will have pulleys so I
could try one and then the other.

2. What length should I cut it for? I am new, don't particular know
what frequency I might be on. I had heard that the 160m loop
(approx. 540' or so) could be good as a multi-band. What exact
length should I aim for, or is it even critical? 1005/?

3. If I use ladder line, I would have to use a balun in the shack
to convert to coax a short run to go to my Kenwood Tuner (which has
160m), on other bands I would use a small Johnson Matchbox which
lacks 160m and eliminate this balun. I am envisioning some kind of
old- fashioned DPDT knife switch, I guess.

4. Actually, as a newbie, I have a nothing but more questions, like
how best to override the built in relay in the Johnson Matchbox
etc. I am gradually figuring this stuff out and hope to find some
locals also.


  #8  
Old April 10th 04, 08:01 PM
Reg Edwards
Guest
 
Posts: n/a
Default

Are you saying that every time you would switch bands or frequencies, one
might
have to change length of feedline? I am trying to picture that, is there

some
convenient solution to this process?

----------------------------------------------------------

No, it is not necessary to change length of feedline for each band. Far from
it.

The tuner will allow you to cover most bands with one length of feedline. If
you are very lucky you may be able to cover all bands with one length of
feedline. No two antennas are alike - and it is just a matter of luck.

You will probably find that, initially, 2 or perhaps 3 bands are difficult
to tune using the tuner. By changing feedline length, up or down, you may be
able to reduce the number of awkward bands to 2 or 1 or perhaps none. As
length is changed some bands will get worse and others will get better.

It is always possible to find a length of feeder which will allow the tuner
to cope with ONE particular awkward band. It is a matter of experimenting
to find a length which maximises the number of bands which can be
accommodated by the tuner.

Hardly anybody is interested in ALL bands. Naturally, you will include your
favourite bands amongst the best. Some tuners are better than others.

---------------------------------------------------

Just to make sure we are on the same page he are you saying to use

this
choke balun just for operation on 160m if I want to use my Kenwood tuner?

I am
assuming that when using the Johnson Matchbox for the bands it was

designed for
I would connect the feed line directly to the Matchbox terminals, and that
feedline would connect directly to the antenna (no baluns, no chokes, or
anything).

--------------------------------------------------------

Leave the 1-to-1 choke balun in circuit all the time, for all bands, and for
whatever tuner you are using.

The sort of problems you will encounter are exactly the same as getting the
G5RV to work on all bands by choosing an optimum length of feedline.
---
Reg, G4FGQ



  #9  
Old April 10th 04, 08:26 PM
Reg Edwards
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Posts: n/a
Default

It should be added, the reason for changing feedline length is to bring its
input impedances on the various bands into ballparks which can be
accommodated by the tuner. Ideally, input impedances should not be VERY
much different from 50 ohms. SWR not much worse than 1.5 or 2-to-1.

The line behaves as a different impedance transformer on every band. It is
a random adjusting process.

In principle, with a perfect tuner, ANY line length would be satisfactory.
----
Reg, G4FGQ


 




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