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Author Topic: Try an indoor 2 meter delta loop  (Read 25516 times)
K2ZS
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« on: February 06, 2011, 03:59:08 PM »

I have seen a few posts regarding indoor 2 meter antennas. I live in an apartment and am not allowed any outdoor antennas. I have tried a few different options for local vhf work and found that a wire delta loop on 2 meters far out performed anything else that I have tried. My first antenna was a Cushcraft AR-270 mounted on a swinging wall mounted monitor support. I could swing it into the window opening when I wanted to get on FM and when not in use it folded back into the corner of the room. This worked well but I always had trouble working a friend on FM simplex. I tried a commercially made twin lead J-Pole that I picked up at a ham fest but that was about the same and only gave me one band. Since I already work with indoor loop antennas for HF use I thought I would give it a try. The received signals are now better and my friend reports my signal has gone up almost 3 S units. I put a new page on my web site at http://www.k2zs.com if your interested in seeing how I made it.

73's
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KE4DRN
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« Reply #1 on: February 07, 2011, 05:23:27 PM »

hi Scott,

Nice construction, I will build one for travel use,
I can always use another antenna!

I am a big fan of the Moxon design.

73 james
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K2ZS
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« Reply #2 on: February 08, 2011, 03:31:19 AM »

Thanks for the reply James. I had never heard of a Moxon antenna until I read your post, that looks very interesting and I think I will try one for my next project. I'm wondering how you change polarization with a Moxon? Do you hang it vertically and have the feed point on the side?
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WB6BYU
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« Reply #3 on: February 08, 2011, 06:05:55 AM »

Yes, a Moxon is basically a 2-element yagi with the ends bent towards each other. 

I've used indoor loops and similar antennas several times.  My favorite approach is to
attach it to a glass window using suction cups - they sell ones with hooks attached
for hanging Christmas lights.  (My current UHF antenna is a 2-wire ground plane hanging
on the window over my desk.)  If you tape the wire to the window glass it will shift
the tuning due to the different dielectric constants, but hanging half an inch away
doesn't seem to make much difference.

If you make the loop rectangular and about twice as wide as it is tall, fed in the center
of a short (vertical) side, it will have an impedance close to 50 ohms and you can feed
it directly instead of using the quarter wavelength of 75 ohm coax.  It isn't as easy to
switch between vertical and horizontal polarization, however, unless you build it on a
frame of some sort.  Otherwise you can use a square loop or triangular loop with the
matching section.

For true vertical polarization the delta loop is fed a bit up from the bottom corner, just
1/4 wavelength down from the top corner.  This probably doesn't make a lot of difference
in your application.  If you use a continuous length of wire for the loop that passes through
holes in the insulators, you can slide the wire around and shift it between horizontal and
vertical polarization without having to untie anything.  In fact, if you installed the loop
with  the top horizontal, you could slide the feedpoint up and down one sloping side
to get both horizontal (at the bottom) and vertical (1/4 wave up from the bottom).

Hmmm...  with your current loop, if you set it up for horizontal polarization (fed at the
bottom point, top horizontal) then you could leave one of the top corners connected
and just swap the other two for vertical polarization - that would still have the top
wire horizontal and the point down, but fed in an upper corner, which gives the same
polarization as when it is inverted.  That might make it faster to change polarization.

A 2-element quad pointing out the window is another step up - I build them using PVC
pipe and #14 wire because that is what I have lots of around the farm, but there are
lots of other methods that can be improvised.
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KE4DRN
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« Reply #4 on: February 08, 2011, 03:38:05 PM »

Hi,

Yes, the Moxon has results similar to a 2 elelent Yagi
but takes up less space and is direct fed 50 ohm coax,
easy to put on a small antenna rotor if needed.

here is another antenna I like to use, the half square on 2m

http://www.qsl.net/kc2jpo/Antenna1.htm

73 james
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KI4SDY
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« Reply #5 on: February 08, 2011, 06:22:23 PM »

This looks like a wonderful inexpensive VHF window antenna. I can't wait to try it. My congratulations on your successful experimentation and thanks for sharing the results with all of us. Cheap too, just the way I like it!  Grin 
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K2ZS
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« Reply #6 on: February 09, 2011, 04:06:39 AM »

Hi James,

Now I'm really interested in the Moxon antenna and am wondering, there is no mention of the distance for the gap at the feed point, is that in anyway critical? Is there a minimum or maximum distance? I looked at one design where someone actually use parts from a commercially made TV Yagi to make his Moxon. The gap at the feed point seems quite wide. Also what about the aluminum mast supporting it? Most other designs use non-conductive material.

Anyway, I'm looking forward to playing with it and thanks for the advice.

Scott
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WB6BYU
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« Reply #7 on: February 09, 2011, 06:21:37 AM »

I've built a couple of Moxons for 2m.  The feedpoint gap isn't critical - the connecting
wires from the coax fill the space.  I use 1/2" x 1/8" flat aluminum stock for the elements,
but they can be made using wire as well.  For vertical polarization you want to keep the
coax and metal mast out of the pattern, most conveniently by rear mounting.  (I use PVC
pipe for my boom with no mast, as the radio mounts on the back end of the boom and
it is intended for hand-held use.)  The spacing between the ends IS important for best
F/B ratio.
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KE4DRN
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« Reply #8 on: February 09, 2011, 03:47:23 PM »

hi Scott,

I built my 2m and 6m Moxon with 3/8" T6061
aluminum tubing, 1/2" pvc pipe and used pex pipe
for spacers on the tails.  For the feedpoint, 1/4" is fine.

I learned about the Moxon deisgn on www.cebik.com

http://www.moxonantennaproject.com/design.htm

73 james

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K2ZS
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« Reply #9 on: February 16, 2011, 04:49:27 AM »

Wow,

The Moxon I built for 70cm worked great! I have the parts for a 2m version and hope to get the time this weekend to build it. Our local VHF group has a net every week. I checked in for the first time this week with my Delta Loop so now I have something to compare the Moxon to.
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K9JCS
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« Reply #10 on: February 28, 2011, 05:42:57 PM »

K2ZS::

Nice project. Thanks for sharing it with us. I tried it and it worked as advertised.

Jim
K9JCS
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KA4NMA
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Posts: 597




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« Reply #11 on: April 28, 2019, 11:39:50 PM »

I am disabled and low income. I can't build any more. Can some

one build it for or me?
Randy ka4nma
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