View Full Version : K0FF 6-Meter Loop antenna - Help!
01-08-2007, 10:19 AM
I assembled most of a 6m Loop antenna today, using K0FF's instructions as given Here (http://www.qsl.net/k4pwo/sloop.htm)
I am new to homebrew antennas, this is actually my first project. I guess I just dont understand what exactly a butterfly is and exactly how it should be attached to the antenna. I have assembled everything but, and not surprisingly have very high SWR without it, so apparently it's important http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif
Can anyone post pictures or give some better instructions for a new antenna builder like me? I guess I just dont get it and I already spent all this money on copper parts that I've hacked up & would really like to get on the air with it.
Attached is a picture of what I have so far...
01-08-2007, 02:18 PM
I would start by double checking your dimensions as your ant does not look the same as the one in the instructions.
the gamma matching stub appears to on a angle instead of parallel to the ant element, suggesting that something is wrong.
also did you strip the outer covering jacket and the shielding off the coax that is inside the gamma ?
The butterfly adjustment is missing from the PVC tee joint. This is needed for series capacitive reactance in order to tune for best match in addition to the gamma match as described in KØFF's instructions. If you read carefully, he indicates the butterfly is made from 1/2"x3" copper or brass. It is mounted to the tee joint (a small, self-tapping screw will do) and is rotated until the proper match is obtained. You can also adjust the length of the gamma rod connection to the drive point of the driven element to adjust for best match as well. I have used two lengths of copper wire at the end of the bent dipole to get best match as well. Simply bend them up and down and all around until the best match is obtained. Somewhat crude, but it works. Good luck.
By the way, the gamma rod probably should be rotated a bit to make it parallel, but it's not critical. A gamma rod is used to make an impedance transformation, and being somewhat non-parallel is minor to the length of the rod. Bill Orr's (W6SAI - SK) Radio Handbook is a good source for explaining how gamma matches work. Look for old copies at hamfests, etc.
73, Jeff K8CQ
01-08-2007, 11:54 PM
The gamma match is crooked because I had been moving it around to try & experiment.
I have the part for the butterfly.. So it just screws in to the PVC & does not make physical contact with the antenna elements? Is this to make a cpacitive coupling, similar to the gamma match? This si what I did not understand about the directions...
I guess I need to pick up a book, no?
Thanks for the help!
01-10-2007, 04:35 PM
bumping to see if anyone knows the answer...
Yes, Paul. You can attach the butterfly with the self-tapping screw to the PVC tee so that the butterfly spans across the ends of the copper pipe, but not touching the pipe. Then rotate the butterfly through various positions until you get the best match. You may also have to adjust the spacing between the butterfly and the copper pipe. As I said in the original response, rather than use the butterfly, I have also used lengths of copper wire attached to the ends of the copper pipe, not touching each other, but close to one another, and bent them around to get a match. About 4 inches long or so. Crude, but it works.
Have you also tried adjusting the tap distance of the gamma rod? This is somewhat critical for the best impedance match.
Good luck & 73, Jeff, K8CQ