Loop Question
 

It looks like I could place a loop around the eaves of my house and it would,
in theory, be resonant around the 40m band. I'm planning on either feeding it
with ladder line or use a 4:1 balun with a very short run into the house.

How can I make the antenna also resonant on 75m? I am planning on using it for
75m-10m.

Randy ka4nma

On 07 Oct 2004 05:39:57 GMT, ospam
(Theplanters95) wrote:

It looks like I could place a loop around the eaves of my house and it would,
in theory, be resonant around the 40m band. I'm planning on either feeding it
with ladder line or use a 4:1 balun with a very short run into the house.

How can I make the antenna also resonant on 75m? I am planning on using it for
75m-10m.

Hi Randy,

It would help to have dimensions. Presumably the perimeter is 40
meters, or thereabouts. As you stand very little chance of one
antenna being resonant on all bands, you may as well anticipate tuning
on the majority of them.

As such, it behooves you to avoid dimensions that are problematic
(presenting a hi-Z impedance). The first likely opportunity will be
with 20M. If you carefully choose your transmission line length to
handle this, you may find you've forced the problem into another band.

As such, some flexibility is in order. One such forethought would be
to have a way to open the loop at the point opposite to the feed (or
perhaps kicks in a tuning cap). This says nothing of the matching
problem that has not already been said (be prepared), but it may be a
simple variation that yields new solutions.

73's
Richard Clark, KB7QHC

Theplanters95 wrote:
It looks like I could place a loop around the eaves of my house and it would,
in theory, be resonant around the 40m band. I'm planning on either feeding it
with ladder line or use a 4:1 balun with a very short run into the house.

How can I make the antenna also resonant on 75m? I am planning on using it for
75m-10m.

Randy ka4nma

Hi Randy,
The best way would be to open the loop on the opposite side from the
feedpoint when you want to work 80m. I would use a relay of some sort
that could be activated from the shack. Also would go with open wire if
possible.

73 Dave

Theplanters95 wrote:

It looks like I could place a loop around the eaves of my house and it would,
in theory, be resonant around the 40m band. I'm planning on either feeding it
with ladder line or use a 4:1 balun with a very short run into the house.

How can I make the antenna also resonant on 75m? I am planning on using it for
75m-10m.

If it is one WL on 40m, it will be 1/2WL on 75m. Install an insulator at the
half-way point. Leave it open for 75m. Jumper across it for the higher bands.
--
73, Cecil, W5DXP

The size of the house is about 25 feet by 40 feet, not including the 2 peaks of
the roof line. This gives a resonant frequency of about 7.7 mhz. The addition
of the two peaks, hopefully will bring it down to the 40m range. I was
thinking of adding a 1/4 wave 75m stub to the antenna.

I am more interested in effeciency and performance than being resonant (yeah, I
know that resonant antennas are more efficient...), but I need a good,
multiband antenna.

Randy

On 07 Oct 2004 18:17:06 GMT, ospam
(Theplanters95) wrote:
(yeah, I know that resonant antennas are more efficient...)

Hi Randy,

Actually, we get many "designs" that are fully resonant and wholly
inefficient. I won't offer the exhaustive list. Suffice it to say
your antenna will be big enough to reduce some inefficiency inherent
in Ohmic losses in the structure, but for the lower bands you will be
in the deadly embrace of nearby lossy ground. You may note this in
the resonance having a broader curve (lower Q) than theory would
provide for the same structure in free space.

73's
Richard Clark, KB7QHC

being tucked under the eves of a house will be neither good nor efficient,
it will be too close to wiring, piping, metal gutters, drip edge, and who
knows what else inside the walls. it will also pick up noise from
everything in the house on receive, and likely get into any poorly shielded
electronic device in the house.

that being said, put up whatever is physically easy to do. leave off the
balun and run to a tuner in the shack and be done with it. it will work
everywhere your tuner will handle it. if the tuner can't handle a
particular band try opening it opposite the feed point or change the length
of the feedline to give the tuner a different impedance to match.

"Theplanters95" wrote in message
...
The size of the house is about 25 feet by 40 feet, not including the 2
peaks of
the roof line. This gives a resonant frequency of about 7.7 mhz. The
addition
of the two peaks, hopefully will bring it down to the 40m range. I was
thinking of adding a 1/4 wave 75m stub to the antenna.

I am more interested in effeciency and performance than being resonant
(yeah, I
know that resonant antennas are more efficient...), but I need a good,
multiband antenna.

Randy

Richard,

On 75m and 40m, I am interested in NVIS. For 20m and above, DX.

The soil is sand - high desert sand. I am also on a hile. On the side with the
feedpoint, we have a small walking space about 20ft from the antenna. After
the walk space, a drop off occurrs of about 40 feet to the next street. The
next side will have one of the eaves and be 15' high then go up the eaves to
about 25' or 30' from the ground, then back down to 15'. The front will be
about 15 feet high. The next side will be like the first one with eaves, and
then back to the backside of the house. I am guessing on the heights.

I am wondering about the 450 ohm feedline. It would pass near (less than a
foot) my pc on the way to the rig and tuner. Would it cause RFI?

I also have an offer of 4 5ft mast. Would it help to use the mast to push the
antenna up a litte more?

On the frount of the house, I am planning on running the wire under a pvc rain
gutter. We have the power feedline coming in from the pole to the service at
the front.

Randy

On 07 Oct 2004 22:47:01 GMT, ospam
(Theplanters95) wrote:

Richard,

On 75m and 40m, I am interested in NVIS. For 20m and above, DX.

The soil is sand - high desert sand. I am also on a hile. On the side with the
feedpoint, we have a small walking space about 20ft from the antenna. After
the walk space, a drop off occurrs of about 40 feet to the next street. The
next side will have one of the eaves and be 15' high then go up the eaves to
about 25' or 30' from the ground, then back down to 15'. The front will be
about 15 feet high. The next side will be like the first one with eaves, and
then back to the backside of the house. I am guessing on the heights.

Hi Randy,

All things considered above tends in your favor - a sort of solution
that when life offers lemons, make lemonade.

I am wondering about the 450 ohm feedline. It would pass near (less than a
foot) my pc on the way to the rig and tuner. Would it cause RFI?

Depends mostly on balance and thus Common Mode issues. Unbalance
arrives by virtue of lack of symmetry somewhere in the system. The
close proximity of the antenna to various structures tends to increase
the likelihood. Anticipate RFI such that you can add a BalUn (if it
makes sense) and cable. The only virtue of 450 Ohm line is in low
loss, but you won't have a long enough run for this to really matter
much.

I also have an offer of 4 5ft mast. Would it help to use the mast to push the
antenna up a litte more?

A 45 foot "mast?" Are you prepared for all the guying? If so, you
could as easily build a top loaded vertical. Don't reduce your
options and walk away from the house-wrapped loop though.

On the frount of the house, I am planning on running the wire under a pvc rain
gutter. We have the power feedline coming in from the pole to the service at
the front.

Well, this speaks to issues of symmetry and balance. This could be
opportunity in disguise (more lemonade) where you put the open into
the loop.

Really, all the compromises you could make (aside from laying it on
the ground) will have negligible effect on performance. Putting it up
higher follows the maxim "more wire - higher" to advantage.

73's
Richard Clark, KB7QHC

Correction! That's 4 masts of f foot length.

Randy

On 08 Oct 2004 06:00:32 GMT, ospam
(Theplanters95) wrote:
Correction! That's 4 masts of f foot length.

Oh! Well, then - nevermind ;-)

I cannot type. I have an offer of 4 pipes of 5ft length. Would placing them
on the eaves help?

Randy

On 08 Oct 2004 21:48:22 GMT, ospam
(Theplanters95) wrote:

I cannot type. I have an offer of 4 pipes of 5ft length. Would placing them
on the eaves help?


Hi Randy,

You mean one at each corner or the house for 5 foot elevation? Or do
you mean all four combined for a one time gain of 20 foot elevation?

I have an Army field grade mast kit with 8 five foot heavy duty pipes
that does a good job (the kit also includes stakes, cording and plates
for 3 tiers of guys, and a 2.5 pound sledge). Works fine, but if I
wanted 20 feet, I would go buy two 10 footers. You have to be careful
these days about your pipe sources. Some in the CIA would claim they
could be used in Uranium Centrifuges and a cruise missile may be
targeting you soon.

If we fall back on the 4 spread among the corners - nah. Too much
work for wholly no observable gain.

73's
Richard Clark, KB7QHC

only if you want the neighbors to think you have an antenna... or some other
weird contraption on the roof!

"Theplanters95" wrote in message
...
I cannot type. I have an offer of 4 pipes of 5ft length. Would placing
them
on the eaves help?

Randy

It would not look good for a preacher to be hit by a cruise missile. :-) Hmmm,
maybe the flaming arrows of spam are from the cia???

Ok, I will scrap the 4 pipes around the house for loop's extra elevation, and
use them for elevation for a 2m J-pole.

With the power company feedline coming in at the front (away from feed point.
would a "U" shape (that is a loop with a gap around the power line) work. I
think that I just realized the answer. It would or could cause an unbalanced
situation which could lead to all sorts of problems like RFI, unable to tune,
etc....

I am also thinking of running the loop along the backside of the house and
then instead of continuing to run along the side of the house, run the wire to
an old unused billboard (about 20 or 30 feet high) and then from the billboard
back along the front of the house, and then instead of along the side, run it
to a tree (the only one on my property) and then back along the side of the
house. The feedpoint would be on the backside about 1/4 or 1/3 from the tree
side.

An idea, if, I use the 2 of the pipes as additional supports placed at the top
of the side eaves , I could run a wire from the tree over the roof to the
billboard, sort of an inverted V or a droopy end dipole with a slight bend on
one side. And if the pipes are placed just right, then I would not be running
a wire under a power feed line, like the loop on the eaves. It would be random
length, and feed about 1/3 or so from the tree end, unless I got more
ladderline. Total length about 60 or 80 feet at about 20 or 30 foot sloping
down to about 10 or 15 feet at the tree. Let's see, a random length dipole in
the clear (by a few feet), should out perform a loop under the eaves? Easier
matching, antenna in the clear, less RFI, better for NVIS and DX. Maybe a
better antenna?

Can an OCF dipole be feed with ladderline?
What is the best way to run ladder line over asphalt shingles?

Randy

On 09 Oct 2004 06:37:43 GMT, ospam
(Theplanters95) wrote:

With the power company feedline coming in at the front (away from feed point.
would a "U" shape (that is a loop with a gap around the power line) work. I
think that I just realized the answer. It would or could cause an unbalanced
situation which could lead to all sorts of problems like RFI, unable to tune,
etc....

Hi Randy,

All of this is actually a long shot - very unlikely. If it DID happen
you have a scapegoat, but RF is not that delicate a flower rent by the
hurricane of speculation. In other words, try it to see if you have
a problem. You will spend far less trying compared to the time
worrying about the possibility.


I am also thinking of running the loop along the backside of the house and
then instead of continuing to run along the side of the house, run the wire to
an old unused billboard (about 20 or 30 feet high) and then from the billboard
back along the front of the house, and then instead of along the side, run it
to a tree (the only one on my property) and then back along the side of the
house. The feedpoint would be on the backside about 1/4 or 1/3 from the tree
side.

Now you are cooking with gas. Imagination is kicking into high gear
and invention is working with real possibilities.

An idea, if, I use the 2 of the pipes as additional supports placed at the top
of the side eaves , I could run a wire from the tree over the roof to the
billboard, sort of an inverted V or a droopy end dipole with a slight bend on
one side. And if the pipes are placed just right, then I would not be running
a wire under a power feed line, like the loop on the eaves. It would be random
length, and feed about 1/3 or so from the tree end, unless I got more
ladderline. Total length about 60 or 80 feet at about 20 or 30 foot sloping
down to about 10 or 15 feet at the tree. Let's see, a random length dipole in
the clear (by a few feet), should out perform a loop under the eaves? Easier
matching, antenna in the clear, less RFI, better for NVIS and DX. Maybe a
better antenna?

Whoops! Backsliding to that familiar nemesis of "a solution in search
of a problem." You are trying too hard to put those tubes to work -
use the abandoned sign. Dare I say it is a "sign?" The metaphor is
certainly not lost on you is it? ;-)

Can an OCF dipole be feed with ladderline?

It typically is and it typically is fed with coax too - howabout that
for political answer - sorry, watching too many debates. We taped the
soap opera when we went out to listen to Mort Sahl here in town. Mort
is getting on in age (wish I could have caught his act at the Hungry I
in Frisco) but he is as sharp as a tack still... and then we got back
for the punch and judy show as a retread. I wanted to throw the
remote at those two monkeys. Politics is a sure argument against
Darwin (evolution caught in a time warp).

OCF guarantees Common Mode for any feed. It is up to you to force a
new balance.

What is the best way to run ladder line over asphalt shingles?

The asphalt isn't a problem, it's the water and crud that comes with
the rain that bridges the wire. Use coax for short runs because you
would need standoffs (like they used to use for TV twin line back in
the old days) but you are back to loss due to water and crud that
comes with the rain that bridges the wire (get the idea?).

Or just simply ignore the loss of the water and crud that bridges the
wire (or ignore the loss of coax) and get on with the fact that no one
can tell the difference with WHAT you use (come what may, rain OR
shine).

One of the supreme ironies is that most folks achieve their greatest
improvements with very little work, and then they have to struggle to
double that performance gain - and then they have to quadruple that
heroic effort to double it again. Ever hear about the problems of
Sisyphus?

73's
Richard Clark, KB7QHC

Ever hear about the problems of
Sisyphus?


No, Can't say that I have heard of that.

The tubes was thinking out loud. I would like the wire to clear the roof, and
I cannot remember if that tree is tall enough. I also cannot remember if the
sign is tall enough -- it is a non standard billboard.

Randy

"Theplanters95" wrote in message
...
Ever hear about the problems of
Sisyphus?


No, Can't say that I have heard of that.

The tubes was thinking out loud. I would like the wire to clear the roof,
and
I cannot remember if that tree is tall enough. I also cannot remember if
the
sign is tall enough -- it is a non standard billboard.

you know what... it doesn't matter. pick one, put up some wire, and put the
rf to it. situations like this are WAY too complicated for even the most
dedicated computer modeler. the best recommendation anyone can make in
cases like this is "Plug it in and try it". if it works, great, if it
doesn't work or causes problems then change something and try again.