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Author Topic: Half wave loop or a bent dipole?  (Read 8070 times)
KB8ZF
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Posts: 25




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« on: April 15, 2012, 04:31:24 PM »

Well I have got my station set up in the apartment here all but one thing the most important thing, the antenna! I live here in a two story apartment building and we live on the top floor, I do have a covered balcony and have been looking at different options for an antenna. I would like to operate as many bands as possible with the limited space I have, so after reading and researching my latest thought is a half wave loop mounted vertically feed at the corner or even a half wave dipole with the end of the legs bent anywhere for 45 to 90 degrees. I am going to cut the antenna for 20 meters and use a Palstar AT2K tuner to tune it with, I wish I could get it to go to 40 meters but I don't know how it would work of even if it will tune. Does anyone think either one or both of these antennas will work decent for a few contacts with a 100 watts. I do not want to use an inside antenna due to rf in the house. One more thing I will be able to mount the antenna mostly out from under the covered balcony.
Thanks
« Last Edit: April 15, 2012, 04:45:31 PM by KB8ZF » Logged
N6GND
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Posts: 354




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« Reply #1 on: April 15, 2012, 05:36:40 PM »

I was in your situation a couple of years ago. I got the most enjoyment out of thinking about every possible wire antenna I could construct. I spent lots of time out on my roof (a single story at one end of the house and two stories to the ground at the other end, but a FLAT roof, easy to walk on and work upon).

I had to consider where my feedline might run. Where (and how) I might put up a pole or mast or several poles to support a dipole or a loop. How to run a dipole essentially north and south so that all of the U.S. would be to the east broadside lobe and Japan (and Russia) to the west. Right in the middle of the roof is a big brick chimney perfect for mounting a mast. Powerlines twenty feet from one end of the roof and the power entry at one corner to be kept in mind.

Lots of fun figuring it all out. And when I made a final decision about what I was going to make and gathered the wire and other supplies, I realized that I had to modify my plans somewhat. And I did.

The dipole, an inverted V with a large included angle, well over 120 degrees, works surprisingly well. North to British Columbia, south to Mexico, all of the U.S. east, Japan, the Land of Oz, Russia.

It was a lot of fun figuring it out. It's fed with ladder line and there is a balun just a few feet from the tuner. It's about 70 ft. long and tunes well on most bands. It tunes differently on certain bands whether I use a 4:1 or a 1:1 balun (there are different theories about this). It tunes easily on 80 and seems to work well there: if I can hear 'em I can work 'em.

Let your imagination fly. Buy some wire and insulators. Or some tubing and build a rotatable dipole for 40 or 20 and feed it with ladder line. Pay attention to the details of construction; some of them make a difference.

Have fun!
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WX7G
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« Reply #2 on: April 15, 2012, 06:27:56 PM »

I used a similar loop from an apartment. A half wavelength loop presents a very high impedance and my tuner would not tune it. So on 20 meters I opened the point opposite the feedpoint to make it a half wavelength open loop. It is a bent dipole. For 10 meters I closed the loop with a clip lead. For the bands in between see which your tuner prefers, open or closed loop.

The loop need not be a square, it can be rectangular or triangular with a perimeter of 36 feet. This antenna can work well on 20-10 meters.

If you want 40 meters from a similar size loop (20 to 33 ft perimeter) the MJF-933 loop tuner ($190) will tune it. I have one of these and it's not bad.
« Last Edit: April 16, 2012, 03:01:18 PM by WX7G » Logged
KB8ZF
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« Reply #3 on: April 16, 2012, 06:12:12 PM »

Well today after looking and trying to figure something out I am just frustrated to the point that I told my XYL I am just going to sell the ham equipment! I have all this radio and can't see a way to get an antenna up, my balcony is about 8'x6' and covered with a 12 inch overhang. We are on the second floor here but nothing I look at seems to be practical or do I have the space for. I can't get up on the roof, it is way too steep even if I could, I was thinking about the vertical 1/2 wave loop or the bent dipole ideal but I don't know if it will work or not because it will be too close to the building itself, also I have to use coax to feed the antenna which that isn't a problem if I can just come up with something that will work. I really don't care about 80 meters either, just 40-10 if possible. I hope somone has some ideals out there or you will be able to find a real nice 1000mp Mark V Field for sale ! 73's
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WB2JNA
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« Reply #4 on: April 17, 2012, 08:09:30 AM »

If you use CW or digital modes, you can do a lot with 5-20 watts output and even an indoor dipole (if that's necessary). You can minimize RF problems by using fairly low power. If you have an external tuner you can try an end fed wire strung indoors, outdoors or a bit of both. It will take some doing, and I have a feeling SSB would be more difficult to make contacts, though not impossible. How about a "hamstick" mobile type antenna, connected to your balcony and using counterpoises for the shiled side of the coax? If you keep trying you'll most likely come up with something that will work!
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WX7G
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« Reply #5 on: April 17, 2012, 11:26:43 AM »

An antenna inside the apartment can work quite well. Don't give up!

If you want plans for a 5' long 20 meter dipole see AntenneX magazine online.
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KQ6Q
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« Reply #6 on: April 17, 2012, 03:24:13 PM »

Before you give up, consider an MFJ 1786 Magnetic loop. It's pricey, but it might let you get on the air!
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N3LCW
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Posts: 139




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« Reply #7 on: April 18, 2012, 09:54:17 AM »

Greg,

I've been through the same frustration as someone living in a strictly enforced HOA neighborhood.  If an 8ft x6ft balcony is what you have to work with then by all means make best use of that!  The suggestions here for either the MFJ 933 Loop tuner or the MFJ Magnetic loop will get you on the air 40 - 10M with a good signal.  Eventually you'll learn enough to venture into building your own antennas, magnetic loop or otherwise.   What you need to do is install an 'effective' antenna.  You need to be able to adjust the antenna to compensate for your environment.  Don't hesitate to get the help of a local club or 'Elmer' with antenna experience.   Read up on antennas as much as you can and get ready to buy an antenna analyzer, a cheap one if you can.  Eventually you'll learn that $5 worth of wire and some salvaged or homemade inductive/capacitive parts can outperform anything else commercially made.

Do a search on Urban Antennas by Igor Grigorov.  That is an excellent book tailored to those of us HOA impaired but not necessarily 'urban':  http://www.antennex.com/shack/Nov01/urbanrvw.html

In my experience I have found these small transmitting loop antennas the most effective for their small size.


Andy
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KB8ZF
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Posts: 25




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« Reply #8 on: April 18, 2012, 04:06:59 PM »

Greg,

I've been through the same frustration as someone living in a strictly enforced HOA neighborhood.  If an 8ft x6ft balcony is what you have to work with then by all means make best use of that!  The suggestions here for either the MFJ 933 Loop tuner or the MFJ Magnetic loop will get you on the air 40 - 10M with a good signal.  Eventually you'll learn enough to venture into building your own antennas, magnetic loop or otherwise.   What you need to do is install an 'effective' antenna.  You need to be able to adjust the antenna to compensate for your environment.  Don't hesitate to get the help of a local club or 'Elmer' with antenna experience.   Read up on antennas as much as you can and get ready to buy an antenna analyzer, a cheap one if you can.  Eventually you'll learn that $5 worth of wire and some salvaged or homemade inductive/capacitive parts can outperform anything else commercially made.

Do a search on Urban Antennas by Igor Grigorov.  That is an excellent book tailored to those of us HOA impaired but not necessarily 'urban':  http://www.antennex.com/shack/Nov01/urbanrvw.html

In my experience I have found these small transmitting loop antennas the most effective for their small size.


Andy



Thanks Andy for all the encouragement, I have been a ham since 1977, I was only 22 years old then and lived in the country. Now I am a lot older (56) and things just don't come as easy as they used to. I am just now getting back on the air after being off for about 10 years. I will check out all your suggestions along with all the other ideals. Yea I just love amateur radio, have built several projects when I had the time but was never confronted with small space antenna situation. I will keep trying and maybe if I can get a good enough signal we can QSO someday. Thanks
« Last Edit: May 05, 2012, 06:45:20 PM by KB8ZF » Logged
K5BJS
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Posts: 50




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« Reply #9 on: April 18, 2012, 08:24:54 PM »

Quote
If you want 40 meters from a similar size loop (20 to 33 ft perimeter) the MJF-933 loop tuner ($190) will tune it. I have one of these and it's not bad.

I can confirm that an MFJ-936B and 26 feet of 4" aluminum flashing (Amerimax 68104) works quite well on 40 meters.
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KB8ZF
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Posts: 25




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« Reply #10 on: April 21, 2012, 05:19:06 PM »

Well today I stopped by the leasing office of the apartments where we live, and ask the property manager about antennas. First I ask about mounting one of those flag poles brackets to the balcony and she said no problem, of course I had to break the ice somehow Cheesy LOL Next I asked about a wire antenna around the deck or balcony, I said I know that TV dish antennas are allowed so what about wire antennas for weather radios and other sorts (had to keep it low key). To my surprise she said no problem! Just as long as can be taken down and not where it would require work to repair after taken down. Now I have an open window to do some things and experiment here, going to add a bird feeder and some hanging ferns and as stated a flag (Old Glory) to the balcony so the antennas will not attract too much attention. Hopefully next weekend will be dedicated to getting something up and try it out.
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WB6BYU
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« Reply #11 on: April 22, 2012, 08:49:29 AM »

Great!  Make sure you use a 16' aluminum pole on the flag - because you are proud of it,
of course.  Then connect the center of your coax to the flag bracket and run a couple
pieces of magnet along the railing for radials...
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KB8ZF
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Posts: 25




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« Reply #12 on: May 05, 2012, 06:43:35 PM »

Well today I had time to make up a coax fed 20 meter half wave dipole. I used clear lexan for the insulators and #26 insulated antenna wire from the Wireman. After making it up I hung the center insulator in the middle of my balcony and ran each leg horizontal as far as possible and the turned them down 90 degrees, I am on the second floor of the apartment building so each leg is still about eight feet off the ground. Then I ran the coax RG8X inside the shack here and hooked it up to my Palstar tuner. I still have a lot of electrical noise but the signals are over it most of the time. Well I didn't expect much on the transmit side but after getting the SWR flat I heard a station and just threw my call out there for fun, and guess what, 5-9 into Europe (Italy) Holy Cow! Thought it must been a fluke but tonight on 20 I have worked state side and also Europe again on SSB with about a hundred watts and no signs of TVI! This is my first contact after being off the air for 10 years! What a thrill, I had almost given up, I am glad I didn't, and the antenna is almost invisible!
Thanks for all the suggestions, I am going to start playing with another antenna also, a loop on the balcony to see what it may do also. 73
« Last Edit: May 05, 2012, 06:46:41 PM by KB8ZF » Logged
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