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help with an attic antenna design

Dutchman II

New Member
Jan 25, 2021
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So after many years I am thinking of purchasing another CB radio, mostly to prepare for emergency use (solar flare, zombie apocalypse).

The house that I live in is approximately 40' tall, so for ascetic reasons I do not want to install an antenna on the top of the house, however, I have a fairy large attic ( approximately 20' x 30' with a 10 foot peak ), so I was thinking of going with some kind of attic antenna, realizing I would be extremely restricted as far as performance using this approach I still think it would be my best option ( although, if I could get away with a horizontal dipole design a few feet above and running along the peak of my house, but that would be a later date, if at all ).

I have been watching You Tube videos and have been watching videos regarding loop antennas, I never really heard of a loop antenna before, but it seems they perform the best of all antennas, so I was wondering, and I imagine you can, is it possible to build a loop antenna for the 11 meter band ? If so, what would be the approximate dimensions and what would be the best way to connect this antenna to the radio, coaxial cable or a ladder design ? I used to have a basic understanding of this stuff, but that has been quite a few years.

My thinking is a loop antenna would be more omni directional compared to a dipole design.

Any advise would be appreciated.
 

Full Wave Loop Antenna Calculator (66pacific.com)

11 meter ant.jpg


Wire Antenna Calculator (ws6x.com)
 
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Thank you for the replies.

After I posted this I noticed I was not in the CB radio section of the website, however, I also recently came across a Ten-Tec Jupiter 538, not sure if it works (although it does seem to receive) and I am not licensed for ham radio, yet, but I could become licensed, so part of my antenna design, or another design, could be for another frequency. Supposedly the more circular the better, thinking I could do an octagon shape, use a ladder line feed and some kind of antenna match system.

I always found the antenna aspect of radio communication somewhat fascinating.
 
Question :

I am pretty sure I am going to go with a full wave octagon shaped design suspended from the rafters above using rope and insulators, not too close to the rafters above, not too close to the floor below. The radio is going to be set up approximately 16 feet below and 16 feet off to the side of the antenna.

Would the coaxial cable connect directly to the antenna ends, OR, would I connect a ladder line to the antenna and then install a Balun to connect to the coaxial cable ?

This part is confusing me, when exactly is a Balun used, is it used for multi-band antennas when the antenna is not matched for any exact frequency ? Or, is a Balun required to connect to ladder line and ladder line is preferred because ladder line is more efficient than coaxial ?

If the antenna wire is cut to length to operate at a certain frequency then would I connect the coaxial cable directly to the antenna wire ends anticipating I may need to adjust the wire end length(s) to get the antenna to match, or is this incorrect ?

Also, expecting I may encounter somewhat higher SWR due to reflected waves inside the attic what would be the best cheapest antenna match set up I could purchase to prevent the radio from seeing a high SWR ?

I know I will be limited with this set up but I would still like to get this to operate the best I can so if I have to do this a certain way then I will try to, my house sits pretty high up compared to my surroundings so I think this might be somewhat successful, all considered.

I made a dipole antenna in an attic once way back when and I believe I got it to match pretty good, I did not even know what a Balun was at that time.

I could probably research and experiment and figure a lot of this out on my own, but if I could skip unnecessary time and money it would be nice. I have watched many You Tube videos regarding this but it is hard to ask a question to a TV and time can be a hard commodity to come by now a days.
 
If you are making the loop for a single band such as 11m, I suggest a rectangle shape. Two oppossing sides are twice longer than the other two sides. Fed in the middle of a short side and you have a direct 50 Ohm impedance match to your coax.
For example, a CB rectangle loop antenna has two sides that are approx. 12' long, and the other two are approx. 6' long. Coax feed it in the center of a 6' side.

I have had an 11m wire loop in my attic for several years just for fun. It works surprisingly well.
 
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If you are making the loop for a single band such as 11m, I suggest a rectangle shape. Two oppossing sides are twice longer than the other two sides. Fed in the middle of a short side and you have a direct 50 Ohm impedance match to your coax.
For example, a CB rectangle loop antenna has two sides that are approx. 12' long, and the other two are approx. 6' long. Coax feed it in the center of a 6' side.

I have had an 11m wire loop in my attic for several years just for fun. It works surprisingly well.

Thank you for your response, interesting that this particular antenna configuration and location of the coaxial connection would yield a 50 ohm impedance, not sure the science behind this but from the YouTube videos I have watched and the various website pages I have surfed this is not normally the case. BTW, curious as to your definition of " surprising results " ?

I am leaning toward a more circular design, although it appears that will present more of a challenge (from what I recall trying to figure this stuff out was half of the enjoyment, and you guys left me out in the woods too long I started researching this on my own), I also want build an antenna(s) that will work on a few different bands, realizing some, more like most, aspects of this are far more complicated than I will ever understand.

I need to brace a few cross ties and clear out some space in the attic to prepare for the build(s).

BTW, I never really cared about looking stupid by asking stupid questions I would rather learn than care about what other people think, again, thank you for your help.
 
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First, by "surprisingly well" I meant that I expected it to do poorly being inside the attic. It surprised me by working as well as it did. Outside loops do better, but I made contacts locally and long distance with it.
I study the science from time to time, but I prefer to build it and see whether it works.
Along the way I learned that impedance changes along the length of a radiator (antenna). Think of the simple dipole, a half wave radiator cut in the middle and fed there. The impedance is ~73 Ohms. Next, make a duplicate half wave radiator but cut it roughly at the 1/3 - 2/3 length and feed it there. The impedance is not 73 Ohms now, but ~100 Ohms. Move the feed point up and down the 1/2 wave radiator and it keeps on changing. I can't tell you why birds get to fly, and earth worms don't, but I know that's the way it is.
I learn just enough science to build antennas and capture RF waves from the atmosphere.
Good luck. If you have half as much fun building antennas as I have you'll have more fun than most folks do.
 
So I am taking it that you used an " antenna analyzer " to have been able to have taken these readings ? If so, were these reading taken directly at the radiator minus any coaxial connection, If that is the case then that will determine whether or not I will need a balun and the ratio of the balun, which is why you recommended your design because no balun would be required, or not ?

So I guess I am going to be needing some type of " antenna analyzer " if I am going to attempt to make a few radiators, any suggestions on a decent analyzer ?

Nothing too fancy, nothing too cheap, something that can provide somewhat accurate readings that may include additional functions that I may also find useful ?

Also, I am guessing I will probably be needing an antenna tuner if I am unable to tune this radiator (due to reflected waves) or if I want to attempt to use this radiator for a different band, OR, if I build another radiator for this Ten-Tec. A manual tuner is fine, something that is decent quality that will not inject any unwanted signals into the system, any recommendations ?

Money is limited with this project, picked up two 490s and I have a feeling this Ten-Tec works, if not I will try to fix it, and radiator wire and coaxial cable is cheap enough, as are baluns and chokes if I make them myself.
 
If a multiband antenna is your goal go as big as you can fit in your space without regard for its shape. Get a tuner. Run a twinlead from the antenna feedpoint as close as you can to the tuner, then transition with a 1:1 balun to a coax to the tuner. If you have a balanced tuner forget the coax.

If you want an 11 meter loop use tuned dimensions, a 2:1 balun at the feedpoint, and coax to your radio. If you use the rectangle shape I suggested, only a 1:1 balun is recommended.

The loop in my attic is a 4 square fed at the corner with a tuned length of 300 Ohm feedline and a 4:1 balun to coax feeder to radio. I don't care about a 1.4:1 SWR.
The rectangle design I have tried only in the open. It worked, then came down as I moved on to other experiments.
A versatile and inexpensive analyzer is the mini 60. Some like the miniVNA. I don't because I dislike the menu layout. I like simple.
 
If a multiband antenna is your goal go as big as you can fit in your space without regard for its shape. Get a tuner. Run a twinlead from the antenna feedpoint as close as you can to the tuner, then transition with a 1:1 balun to a coax to the tuner. If you have a balanced tuner forget the coax.

If you want an 11 meter loop use tuned dimensions, a 2:1 balun at the feedpoint, and coax to your radio. If you use the rectangle shape I suggested, only a 1:1 balun is recommended.

The loop in my attic is a 4 square fed at the corner with a tuned length of 300 Ohm feedline and a 4:1 balun to coax feeder to radio. I don't care about a 1.4:1 SWR.
The rectangle design I have tried only in the open. It worked, then came down as I moved on to other experiments.
A versatile and inexpensive analyzer is the mini 60. Some like the miniVNA. I don't because I dislike the menu layout. I like simple.

Yeah, from the research I was doing that is what I figured, if I went with a full wave loop for the 11 meter antenna, then I would use a 2:1 balun.

I plan on building 2 separate antennas in my attic, hopefully they will not interfere with each other, one loop antenna tuned specifically for 11 meters, because it will be in attic antenna the plan is to build it precisely as possible, I want the antenna to propagate the best it can only using a tuner if I have to for a safe SWR.

The second antenna, a loop also, as you said pretty much as large as I can, figure I should learn a few tips from the 11 meter build.

I am in the process of ordering the supplies for the antenna build off the internet, I am still researching the antenna analyzer, thank you for your assistance.

BTW, I did a lot of research into car audio SQ, not into the equipment side, but the speaker side, bought an old tube type HP signal generator, RMS analog AC volt meter, and a frequency counter off E Bay so I could build my own custom Zobel networks for my higher frequency speakers, a Zobel network helps to stabilize the impedance that a passive (capacitor(s) and coil(s)) crossover network sees so the network acts stable and only passes the desired frequencies to the speaker (a speakers impedance rises as audio frequency to the speaker rises), I mixed and matched various capacitors and resistors and charted the results until I found the optimum components, I made a lot of mistakes and endless experimenting (which is what I was trying to avoid here), but I eventually pretty much figured it out. If I ever get this entire design installed in my newer vehicle I think it would be really special ... figuring this experience will prove to be helpful, as mentioned, I am far from an electrical guru, always found antennas and speakers interesting, looking forward to the long wave build.
 
I am sure your audio will turn out great.

About the large loop. . . Have you considered running it outside all around the perimeter of your roof tucked under the edge of the shingles?
Image shows a dipole, but it could be a loop, too.
Screenshot_20210206-094733_DuckDuckGo-01.jpeg
 
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I don't know, personally.
Those with antenna restrictions look for ways to get on the air. This has been an option for a stealthy approach. I intend to try one just for the fun of it when I get some time.
 

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