Full Wavelength Loop

[HomerBB]

what frequency are we talking about here ???????

For CB
Sometimes a little freebanding above and below.

No ham license at this time.

 

[1342]

Situation:

I have a full wavelength loop in my attic. SWR is good 1.4:1 in channel one, 1.1:1 on channel 40. It works fine, but is in the attic with the attendant impact on signal being there causes.

Thought:

I want to move it to the roof, but the roof line will bi-sect two of the quad shaped sides of the loop giving the loop two angled sides and two straight non-angled sides. The 5/12 pitch of the roof will give me about a 22.5* angle in those two sides.

Question:

Is this workable, and, if so, how might it affect the antenna.

The question is about expected performance due to being above the roof, and how the bending of the two sides might affect it's performance.

Currently it is mounted horizontally and fed from the corner matched with a 1/4^ 75ohm section to rg58U.

hey homer i built one of these a couple days ago length was 36.5 feet with 9.1 ft of 75 ohm i laid it on my addition(almost flat)in a square but have not got the match below 3 yet any tips would be great.oh and where is your 75 ohm at compared to your antenna under,away,vertical,inside or outside your loop and did you have to trim your 75 ohm shorter at all thanks.

 

[W5LZ]

1342,
There are two things that are going to affect your loop dramatically. The first is that it's laying on that roof. That means that the resonant length isn't going to be close using the normal formulas. I would think that the total length is too long, but no idea how much.
The second thing is that length of 75 ohm coax used as a 'Q' section (matching section), it's almost a 1/3 too long. The electrical 1/4 wave length for it is close to 6 feet, not 9 feet. [246 x .66 = 5.96 feet ~ call it 6 feet]
I would think that shortening the 'Q' section, then hunting for a low SWR would be one way of figuring how much to shorten the size of the loop. 'Course, if you happen to have a grip-dip meter, or an antenna analyzer, either of them would make it easier or at least faster.
- 'Doc

All of the 'numbers' above are only 'ball-park', none exact.

 

[HomerBB]

I agree with Doc

My antenna is in the attic, but is suspended horizontally from the rafters hanging in free space, not lying on anything.

As I recall, I used the Q section formula Doc showed us, and then trimmed the loop to obtain the SWR just as he suggested.

I started with a 36 feet length loop wire.

I feed from one corner, and the feed line is drawn away from the loop not passing under or through the loop anywhere.

 

[1342]

thanks for the fast response guys i originally cut this for 27.475 and have not figured a mounting setup i put 4 bricks up there for now to keep its shape even with the match above 3 i can receive almost as good as my v 5/8 40 ft to base or 30 ft above loop and did make 3 contacts that were very good reports i will do some trimming and get some bamboo thank you..

 

[1342]

after my imax snapped i put this homemade dipole up vertical not quite as high as you can see but it matched to 1.1 with no baluns or tuners just wire to coax to meter.had several skip contacts and local talk to 70+ miles.hooked on top with bamboo at 90 degrees plant hook to hang and duck tape holding the bamboo on top.homemade vertical 8 bay in backround for hd.