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Author Topic: 3 Half-Wave Dipole  (Read 3698 times)
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Ed WA4NJY
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« on: July 18, 2022, 05:02:40 PM »


   I would like to have a dedicated bi-directional antenna for 15 meters.  A little gain would help.

   Is the 3/2 wave dipole have any real advantage over a regular half-wave at same height?

   Either one is an easy install.   Any input will be muchly appreciated.

   Thanks,

        Ed WA4NJY
        Bradenton, Fl
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M0VRF
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« Reply #1 on: July 19, 2022, 12:03:15 PM »

Works on 40 as well with conventional pattern however 3/2 has deep nulls, close to gnd or inv V prob omni anyway..
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WU2D
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CW is just a narrower version of AM


« Reply #2 on: August 14, 2022, 09:19:27 AM »

Just another proven solution: A vertical loop only requires two supports and two lower guys- it is basically two dipoles in phase and is bidirectional. When square it is easily matched with a 2:1 Balun. When Rectangular you can easily hit 50 Ohms. Here is a nice article showing a 15M and nested 10M loop setup.

https://va3stl.wordpress.com/2010/08/11/dual-band-rectangular-loop-antenna-for-15m-and-10m/
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These are the good old days of AM
K9MB
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« Reply #3 on: August 14, 2022, 10:06:12 AM »

Maybe you would like an extended double zepp.
It gives you two half waves in phase and some gain over a dipole plus a clean bi-directional pattern.
I built an array using this antenna for 20 meters that included passive reflectors and directors so that it became two 3 element yagis mounted side by side.
It can also be built as an inverted vee.

https://www.google.com/search?q=extended+double+zepp+inverted+v&rlz=1C9BKJA_enUS931US931&oq=extended+double+zepp&aqs=chrome.2.69i57j0i512l2j0i22i30l3.16612j1j7&hl=en-US&sourceid=chrome-mobile&ie=UTF-8


I agree that the delta or quad 1 wavelength loop is an excellent antenna.
73, Mike
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WA4WAX
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« Reply #4 on: August 14, 2022, 06:34:49 PM »

An 8JK would be made to order for your situation. 
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Ed WA4NJY
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« Reply #5 on: August 15, 2022, 06:17:01 PM »


   Many thanks to all who replied to my question.  I am leaning toward a rectangle loop for 15.  The project will have to wait until weather cools later this year.

               73,
                    Ed  WA4NJY
                    Bradenton, Fl
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R. Fry SWL
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Broadcast Systems Engineer (retired)


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« Reply #6 on: August 16, 2022, 07:01:27 AM »


   I would like to have a dedicated bi-directional antenna for 15 meters.  A little gain would help.

   Is the 3/2 wave dipole have any real advantage over a regular half-wave at same height?

The study below may be one solution.  This configuration smooths out the deep nulls in the pattern of a linear 1.5WL antenna, and has a fair amount of gain over a linear, 0.5WL horizontal dipole.

RF (W9XMT)

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WA4WAX
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« Reply #7 on: August 16, 2022, 12:05:26 PM »

Try this simulation:

15 meter 8JK 25 feet up and 18 feet up.

Dimensions:

Wires 18 feet long.  5.5 feet separation.  End fed with 3/4 wave Zepp feeder.

My money says it beats the loop.
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K2WW
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« Reply #8 on: August 17, 2022, 07:17:52 AM »

Lookup
"half-square" bi-directional and low to ground/low angle radiation

73
Dean
K2WW
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K9MB
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« Reply #9 on: August 17, 2022, 09:42:05 AM »

Lookup
"half-square" bi-directional and low to ground/low angle radiation

73
Dean
K2WW

Very interesting antenna. I had not considered one because My towers were only 60 feet, but Rudy Severns N6LF published this article in ARRL Antenna Compendium 5 and he also has it on his site. Great idea. MB

https://rudys.typepad.com/ant/files/antenna_halfsquare_array.pdf
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N4DJ
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« Reply #10 on: January 21, 2023, 06:52:10 PM »

I use both a Half wave dipole cut for 15 meters and a Dipole cut for the CW end of 40 meters for 15 meters.
The dipole gives about 7 or 8 dBi gain broadside. Its about 40 feet high. The 40 meter dipole gives maybe a bit more gain but in four narrow directions. If I did not need an antenna for 40 meters I would just as soon have two 15 meter dipoles at right angles. I did something similar for 10 meters this year. I ended up with three dipoles, one NE/SW, one E/W and one N/S on a 3 position remote switch. Sometimes switching gave me one or two S-unit increase. Peak gain from EZNEC was almost 8 dBi and the minimum gain at any point was only down 3 dB down from that with one of the three antennas and that was only at precisely two compass points. I have had large Yagi's on Ten Meters and switching between the three dipoles felt like instantly swinging a Yagi! A dipole is really good if high and broadside to your desired direction. Its the nulls on any antenna that really hurt. The null off the end of a good dipole can be two or more S-units. Some longer wires have more nulls. I think nulls are bad and want to avoid having them as much as possible.

One note about loops. A Quad loop is never going to be more than two in phase stacked dipoles with their ends bent down with 1/4 wave spacing. Two in phase dipoles stacked at 0.6 wavelength might give almost 5 dB gain over one but stacked at 1/4 wave the gain drops to 1 dB. The Quad loop is definitely no more than that and I think a bit less. Other loops will be even worse that that.


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K1JJ
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« Reply #11 on: January 21, 2023, 09:29:21 PM »

Hi Ed,

It is hard to find an antenna that is physically simple, environmentally stable, unidirectionally switchable, has a fat, clean, broadside pattern -   and has good coverage and can use coax.

To fit the bill, I'm thinking you may consider a pair of driven, phased, 1/2 wavelength dipoles. Hang them on a catenary rope or steel cable (like a Yagi)  stretched between two trees.  Inverted Vees are OK; flat elements are better.  Feed with RG-213 (or what have you) with equal length feedlines for each dipole.  Space the dipoles apart 0.2 wavelength.  Run the two coaxes into the shack and in the comfort of your home  tie the feedpoints together for a bi-directional pattern. Or, add  ~1/4 wavelength coax length to one side to experimentally find the best coax length for best f-b unidirectional. (times coax velocity factor)  Use a relay to switch it in the other direction.    You can fine tune the match for best swr later on.

There's nothing like having a receiving antenna with a 20+ dB f-b ( cancel noise from an entire hemisphere) and forward gain of 5 dB over a dipole. If interested, there's a lot on the web about using a pair of phased dipoles.

Tom, K1JJ
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km6sn
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« Reply #12 on: January 22, 2023, 12:41:19 PM »

Just another proven solution: A vertical loop only requires two supports and two lower guys- it is basically two dipoles in phase and is bidirectional. When square it is easily matched with a 2:1 Balun. When Rectangular you can easily hit 50 Ohms. Here is a nice article showing a 15M and nested 10M loop setup.

https://va3stl.wordpress.com/2010/08/11/dual-band-rectangular-loop-antenna-for-15m-and-10m/
The grand dame of ham radio, Allison KB1GMX,  says that the loop antenna dimensions shown in that article results in an antenna where, with 5 watts on 10 meters, you can work anything you can hear.
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