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Author Topic: Indoor antenna  (Read 3032 times)
W5WSS
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Posts: 1744




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« on: December 19, 2012, 04:24:01 AM »

Has anyone linear loaded a rectangular vertically oriented loop that is .75 wavelength perimeter.

I am striving to build an antenna that maximizes manifested power in low enough trajectories to be useful for the longer range dx that which a horizontal version ends up too low to the ground from the indoor ceiling, this is primarily a "too low" to the ground issue for the horizontal family of antennas on 20M about 20ft.

I have been working towards this goal but after many years of experience The prognosis is almost futile.for 20m and reliable longrange performance on 20m at 20ft low.

I have succeeded in a vertical that fits a space and does hear and contacts longrange dx stations on 10m 12m 15m and a little less on 17m but is dead to the same distances by the time i get to 20m.

I must try something and thought I would ask here and see if anyone can suggest something that raises the distance footprint for 20m.

I am convinced I must build and try a second antenna IE that I will need two antennas indoors and live with the mutual coupling of everything about the environment.

If I could get 30degrees of trajectories and omni directional I would call it a victory.

Thanks 73
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N0SA
Member

Posts: 16




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« Reply #1 on: December 19, 2012, 04:35:09 AM »

Have you given any thoughts to a magloop.
A 20M to 10M magloop is a good alternative.
Larry
n0sa
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W5WSS
Member

Posts: 1744




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« Reply #2 on: December 19, 2012, 04:50:34 AM »

yes but I am under the impression that the magnetic lines of force about the antenna switch to electic and the antenna does not really overcome low height.

I am interested to know if the antenna is capable of working longrange dx through a wall and from low height?
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VE3FMC
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Posts: 987


WWW

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« Reply #3 on: December 19, 2012, 07:09:31 AM »

yes but I am under the impression that the magnetic lines of force about the antenna switch to electic and the antenna does not really overcome low height.

I am interested to know if the antenna is capable of working longrange dx through a wall and from low height?

You are asking a lot from an indoor antenna at low heights. If I were you I would be happy with any results let alone DX.

Go read the info on AA5TB's website http://www.aa5tb.com/index.html
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K7KBN
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Posts: 2813




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« Reply #4 on: December 19, 2012, 08:46:36 AM »

Experiment away!  By the time someone on a forum gives you a response you like, you could have built a prototype and tested it.
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73
Pat K7KBN
CWO4 USNR Ret.
WB6BYU
Member

Posts: 13335




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« Reply #5 on: December 19, 2012, 08:59:16 AM »

There are lots of issues with indoor antennas, including coupling to the wiring,
plumbing and ducts, attenuation of building materials, and, of course, a severe
limitation on space.  Some of those things you have control over, some you
don't.

Here is the approach that I would take, which might be similar to the question
you are trying to ask.

1)  determine if there is a preferred direction of radiation.  Don't expect more
than about a 3dB front/side ratio, but if there is a favorite (bidirectional)
target, you may be able to optimize the antenna for it.

2)  Use the standard formula for a full wave loop and cut a wire perhaps 10%
longer than that.  (The more you bend the wire around, the longer it has to
be for resonance.)

3)  Choose two locations for the vertical radiators.  If these are close to each
other (a few feet) the antenna will be omnidirectional (at least as much as
the building environment allows).  If you separate them at opposite sides of
the room, the antenna will have maximum radiation broadside to the two
verticals, but with a fairly wide pattern.  Corners of a room tend to work
well for this.

4)  Put your feedpoint in the middle of one vertical section and run the wire
from floor to ceiling.  Find the opposite point on the loop and make that the
center of the other vertical radiator.  String it up so there are no other wires
running from floor to ceiling:  that is, the floor ends of both vertical wires are
connected together.

5) Arrange the remaining wire on the floor or ceiling as appropriate to use up
the excess.  Running it around the top/bottom of the walls is usually a good
choice where it fits.

For example:  say your room is 8' x 12' and 8' high.  A full wave wire for 20m
will be about 80' (allowing some extra).  The two 8' vertical wires will use up
16' of that, leaving 64' (or 32' each on the ceiling and floor)  If the two wires
are close together, the wires could make an 8' square (running just 8' down
the 12' wall, then cutting across to the other side.)  If the vertical elements
were at opposite ends of the 12' wall then running around the edge of the
ceiling would only use up 8 + 12 + 8 = 28', and you would need to add some
extra bends (down the opposite wall, back towards the center of the ceiling,
etc.) to use up the extra wire.

Check the resonant frequency, and adjust the extra wire as needed to bring
it to resonance in the 20m band.  There may be some advantage in trying to
keep the top and bottom wires mirror images of each other, but it isn't the
end of the world if that doesn't work.

The wire on the floor can be covered by a carpet.  Losses will be higher if
you have a cement floor, or electric heating elements embedded in it.

Basically  you've built a full wave quad loop with some "linear loading"
(even if the wires don't run exactly parallel in most places.)  With any
closed loop the point opposite the feedpoint is always a point of maximum
current (hence maximum radiation).  With a full wave loop the feedpoint is
a second such maximum, which is why these two portions are arranged
vertically and the rest of the wire simply strung around however it fits.
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KK5J
Member

Posts: 81




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« Reply #6 on: December 19, 2012, 09:21:25 AM »

Move into a house. Live happily everafter in ham heaven. The end. Shocked
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W5WSS
Member

Posts: 1744




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« Reply #7 on: December 19, 2012, 09:29:58 AM »

OK thanks Dale, Yeah perhaps some form of half square where the horizontal wire is a transmission line feeding two vertical drops.

Yeah and hope the bidirectional pattern develops afterwhich I purposely aim for perhaps NE-SW.

I already have  a 16ft vertical wire dipole that I can easily tune to load  power and present power to the antenna on 20m band with the wide range tunerand integral 1:1 current balun that is directly at the feed pointand better yet devoid of any antenna feedline but it is absolutely deaf to DX but Very good high angle skywave sensitivity.

Very frustrating....

I am thinking that A loading coil or resonance in my mind would not change the apparent destructive mutual coupling that I think is happening to 20m long range dx skywave.This is a painful issue because I know it is existant and strong enough to be heard but just not into this antenna here.

I suppose if I relocate the thing somehow perhaps I would get lucky dunno.

Any additional thoughts?
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W5WSS
Member

Posts: 1744




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« Reply #8 on: December 19, 2012, 09:31:35 AM »

KK5J Smiley
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W5WSS
Member

Posts: 1744




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« Reply #9 on: December 20, 2012, 08:31:52 AM »

Dale do you have a sketch I am trying to follow along.

 80 ft of wire shaped into two loops positioned directly (BEST) above the other.

 Spacing is between the ceiling and floor.

The vertical portions are both broken open and fed.
The location of the break is in the center or 4ft spot.
The spacing of the two vertical drops are close like a ft.

This is a good idea and I have half of that now I will try it.

The half that I have I press into multiband service and works well on longrange dx skywave on 12M 15M and 18M
but is deaf on 20M relative to long range dx skywave only.while it is very very good for stateside dx skywave maybe designing and building for 20m monobanding one can electrically change some of whatever is destructively killing the manifested power in the low enough angles for 20m dx skywave work.

I will try it interestingly worthy to note I am already on track with half the design anyway.

Thank
My email address is good foralwaysblessed@aol.com

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W5WSS
Member

Posts: 1744




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« Reply #10 on: December 20, 2012, 08:56:10 AM »

I can feed from a desktop wide range tuner and balun.
Completely eliminate any antenna feedline.

Therefore designing for 20M will INCLUDE 20m and simutaneously this design is multibandable.upwards in frequency.

Destructive mutual coupling to be analysed.

I have not checked email after some thought about 2 minutes" i see the antenna and do not need a sketch

Thanks
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WB6BYU
Member

Posts: 13335




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« Reply #11 on: December 20, 2012, 09:21:19 AM »

While such a design works well at the fundamental frequency, at twice that the currents
in the two vertical sections will be out of phase, which will change the radiation pattern.
If you want broadside coverage on all bands then a better approach is to feed both
vertical sections in parallel:  that forces broadside radiation on all frequencies. 

Probably the easiest way to do that is to run equal lengths of ladder line or twinlead from
each feedpoint to the back of the tuner.  Then just arrange the rest of the wire however
it fits on the ceiling and floor.

There is no advantage to avoiding the use of feedline in a properly designed antenna.
Sometimes (as in this case) it is needed for the antenna to work right.
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W5WSS
Member

Posts: 1744




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« Reply #12 on: December 20, 2012, 09:55:25 AM »

Ok thanks. Please send me a sketch as I am not able to visualise your suggestion via the postings here.

I would prefer your design for omni directional ish coverage.
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WB6BYU
Member

Posts: 13335




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« Reply #13 on: December 20, 2012, 01:03:45 PM »

Unless you can get the two vertical parts more than a quarter wave apart, it don't be
very directional - just a little better in the broadside direction.

I can send you a sketch, but let me see if I can explain it more clearly for other readers.

Let's start with a square quad loop, fed in the middle of one vertical side.  Maximum radiation
is from that point and from the opposite point in the loop (also vertical).  This still holds
true if we stretch the loop out and make it longer but not as high.  If we make it about
twice as long as it is high (for roughly the same amount of wire) then the feedpoint
impedance drops close to 50 ohms (in free space, at any rate) and it is a convenient
antenna for a direct coax feed.  This would be roughly 13' x 26' for 20m.  If our
ceiling isn't that tall we can keep stretching it out and making it shorter, while adjusting
the wire length slightly to keep it resonant on 20m.  The feedpoint impedance lowers
even further (you'll probably want a 1 : 1 balun on your tuner rather than a 4 : 1 to
reduce losses) but the same principle applies.  Eventually we stretch it out to about
8' vertically and 30' wide, and it is short enough to fit between ceiling and floor... if
your room is long enough.  What if it isn't?  Then bend the horizontal section around
to make it fit the space available.

For example, if your room is 10' x 10' and you need to use up 30' of horizontal length,
then put the first radiator in one corner, run the wires around 3 of the walls (top wire
at the junction of the walls and ceiling, bottom wire at the junction of the walls and
the floor) and put the second radiator in an adjacent corner.  If the room still isn't
big enough, move the radiators closer together until you use up all the horizontal
wire running around the walls.  Even an 8' square room should be big enough to hold
this antenna if it has an 8' ceiling.

Now, that's the original idea for monoband operation, but the current distributions aren't
optimum on the higher bands: we want to keep the current in phase in both vertical
sections.  The easy way to do that is to feed them in parallel.

So let's go back to the original square quad model.  Rather than feeding it in one
vertical side, we can feed both vertical sides in phase:  the currents are
in phase in the two sides anyway, so the radiation pattern is the same.  Let's do
this using a quarter wave of 300 ohm twinlead from the center of each element,
connected in parallel at the tuner.  (In practice we would use whatever length
of feedline fits our installation, as long as both pieces are the same length.)

Now we can install the antenna the same way we did in the other case, with the
horizontal wire wrapping around 3 or more walls.  Now we don't have to worry
about tuning the loop because we are forcing the currents to be in phase regardless
of the loop size - all we need to do is to adjust the tuner for a good match.

There is still one problem, however:  the current distribution on 10m will have a
current minimum at the feedpoints, with maximum radiation from the horizontal
wires rather than the vertical wires.  We can fix this by shortening the overall
length of wire in the loop by around 1/4 wavelength from both the top and bottom
horizontal sections.  (So perhaps 20' to 22' for the horizontal section rather than
30'.)

The feedlines can be open wire line or twinlead, both pieces the same length.  I'd
just use whatever length I need to go between the two feedpoints.  If that doesn't
give you a convenient spot for the tuner then you can use a longer piece from
each side, or join them and run another convenient length of feedline from there
to the tuner.  You might need to experiment to see whether a 1 : 1 or 4 : 1 balun
on the tuner makes it easier to match.


For a smaller version, build a 10m full wave loop, which will be something like 8' high
and 9 or 10 feet wide, fed in just one of the upright legs.  And, um, that's it:  use
a tuner on 20m through 10m.  It's a half wave loop on 20m, so will have a high
feedpoint impedance and a low radiation resistance, with the far end providing most
of the radiation.  On 10m it radiates from both vertical sections as a standard full
wave loop, with varying ratios on the other bands.
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W5WSS
Member

Posts: 1744




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« Reply #14 on: December 21, 2012, 06:17:08 AM »

Thanks Dale, Yes now I understand. a vertically oriented loop installed on a wall.

The smaller version will fit.
I have 8ft vertical space available Floor to ceiling.
I have 14ft horizontal space available...44ft

I will make a loop to fit a space on the wall an outer wall to the outside.

I will feed it in the middle of one vertical portion at 4ft.

As I recollect the rectangles are a little low for feed point resistance this may be a little higher.

It will be a rectangular shape almost 2:1 squish ratio.
The RR and feed point resistance will be compensated via a wide range T-match tuner that has an integrated 1:1 current balun and should handle the various matching challenges for the multi band excursions. 20m-10m is fine to me.

I can first try coaxial cable and then if needed turn to the family of open wire balanced lines but I suspect a lower impedance line eases the pressure on the tuner in this case,

The goal for lower angle (lower than a horizontal low antenna hopefully) vertical radiation.
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