homemade full-wave attic-mount loop

[mouserusker]

I'm setting up my first CB home station. It's actually my first transceiver setup of any kind.
I got a copy of the ARRL Antenna Handbook, read lots of things on the internet, and came up with this loop. (Pics below)
It's 38 feet (slightly longer than one wavelength at 27.205, as per the chapter on loop antennas) of 12 gauge copper wire. Height is 74" and width is 154". It's fed halfway up one of the vertical sides with a Q-section made of 75 ohm coax 5 ft 11.6 in long (1/4 WL x .66 (velocity factor for solid de coax)). This is coiled for common mode choking and attached to 50 ohm coax coming from my Galaxy DX959.
So, what do you guys think? I'm really new at this, so I welcome advice and harassment. Thanks!

 

[Wire Weasel]

Well it's an interesting start. I love loops and have an 80 meter horizontal loop up in the backyard for all of my HF work on 80,40,20,17 and sometimes 12/10 meters. Also tunes up on 6 meters at 50mhz with a good enough outboard tuner.

Problem with your loop here is that loops have NO gain on the fundamental frequency....the bottom freq. that it's made for...which in your case is 11 meters. But they do increase in gain as you increase in frequency with them. (higher bands on multiple wavelengths)

So you have a no-gain antenna. You can do way better than that with pretty much anything. A dipole, An Antron 99....anything.

Also, vertical loops will be directional out the front & back with considerable nulls out the sides. This will further limit what it can do for you.

Fun to make, talk on where you can, and experiment with. It's certainly stealthy....why...it's darn invisible from the outside!

Good luck and have fun!

 

[W5LZ]

Just a very slight 'correction' about that gain thing. A full wave loop does have some slight gain, and that's when compared to a 1/2 wave antenna. Don't misunderstand, that gain is VERY slight, not worth the trouble for the gain alone. But, there are other features or characteristics of loop antennas that can make them desirable besides gain.
(I like loops too, BTW.)
From what I can tell from the pictures, your loop appears about normal, so it ought'a work about normal for an 'indoor' antenna.
- 'Doc

 

[packrat]

Very nice work there. Very clean!!

PR

 

[mouserusker]

Thanks for the replies.
I don't own a tuner, so I'm kinda stuck making resonant antennas for now.
From looking at my own pics, it looks like maybe I'll want to strip the foil shield on the 75 ohm coax back a little further from the washer/bolt where I've connected the center conductor.
W5LZ, I was hoping you would comment. I've learned from other threads that you are a loop guy, and I was hoping you'd tell me if I did the Q-section properly. I used a lot of terms in my opening post that I have only the loosest grasp on. Basically, my main concern is achieving a low SWR without the use of a tuner.
My girlfriend asked me what I was doing when I had several textbooks and websites and QST mags open along with my notes and journal/planning book all opened out in front of me. I started explaining standing waves and impedance, and after only a couple of minutes she looked sorry that she had asked and I summed it up by saying it was magic.

 

[HomerBB]

I have a similar loop in my attic just for fun. The difference is I laid mine flat so as to have potential communications with verticals in the area. I've talked local and DX with it, but not much as any of the outdoor antennas - horizontal dipole, 2 el quad, A99, 2el yagi, inverted V dipole, 3el yagi, 5/8^ vertical, 1/4^ coax - I've used out performed it. Only the A99 was store-bought. Nevertheless, it's still in the attic and I switch to it for fun now and again.
BTW, your work looks good.

 

[Captain Kilowatt]

Not bad,not bad at all. I have seen far worse from folks into radio for a dozen years or more.

 

[W5LZ]

I'm not sure what else I can say about it. It appears to be workable, it ought'a work. Without getting my hands on it, and just trying it, anything I say would just be a guess.

I can give you a few general thingys about loops that you probably already have been expeosed to from your research.
The first deals with positioning, directivity (which that positioning affects) and polarization (loops can change polarization by where you feed them). Except in sort of rare instances, I've appreciated having an omnidirectional antenna more than a directional one. That's cuz I wanna hear everything, not just from two directions. Not everyone feels that way so it's a personal foible, sort of. I also seldom have the means of hanging a loop vertically to get that directionality, that probably has a lot to do with it too .
Polarization can be changed by feed int that loop in different places. Easiest example of that is with a 'square' loop. In one corner, it's vertical, on a top/bottom side it's horizontal. Same thing happens with almost any shape of loop, but the 'where' can change to some weird places because of some kind'a weird shapes, you know? In one or two loops I've used, I just didn't worry about polarity. I'll blame that off on them being of really 'odd' shapes and I didn't know where the @#$$ to feed it to get any particular polarization, that sort of thing. They worked for what I wanted them to do, so I just didn't care.
I like horizontal loops. Mainly because I couldn't stand them up, no room for their size, and except for those rare instances, I wasn't too interested in them being directional. If you can pick their shape (within reason) they can still be directional.
I also cheat when I can. I don't use coax as a feed line unless I have to. That means that with the right sized tuner and a little 'fudging' here'n'there, I can make them work on higher frequencies pretty well, sort of. (It's dangerous enough getting through my back yard with the wild animals, quicksand, and stuff without having to worry about where to put a bunch of other antennas I probably don't have room for anyway. Which doesn't say anything about threats from the neighbors,etc.)
And all of this stuff is variable. Meaning the results vary for each particular circumstance.
- 'Doc

Best thing I've learned when dealing with antennas is how to cuss. You'd be amazed at the times that's come in handy. Not just with antennas! I do have a bad reputation to maintain, and it ain't as easy as you thing, I'll have you know.