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