Non-resonant horizontal loop question
I strung what turned out to be roughly 420ft of wire, hoping I could fit enough for 160m, but ran out of space. It's a fairly wide rectangle shape, with the feed point a little off-center of the long side. Height isn't great, roughly 25ft most of the way. It's coax fed using a 4:1 balun, as I'm using an auto tuner with no balanced input. It loads almost anywhere, but obviously I was hoping for either 80 or 160. Performance is less than desirable.
Kind of wondering what my options might be to make something better out of this attempt.
The antenna should perform about like a dipole up 25 feet. The VSWR on the coax is quite high and if the length is long the loss is high.
1) How much and what type of coax are you using?
2) Is the balun a current or a voltage balun?
3) If it is a current balun does it use one ferrite core or two independent ferrite cores (that's the right way to do it)?
After reading your post several times, I'm afraid I'm still vague on several points, especially on exactly why you are disappointed in the performance. Does the antenna not hear as well as what you are used to? Are you having trouble making local contacts, or DX ones?
How high is it? Generally speaking, we don't expect a horizontal loop to perform well at all as a DX antenna on the fundamental band. It will not work well for DX on the first harmonic unless it is at least a quarter-wave high on that band. This is (obviously) sixty feet on 80m. It is on the second harmonic, 40m for a 160m loop and 20m for an 80m one, that the antenna begins to come into its own as a DX antenna; and it will still work best provided it is at least a quarter-wave high on those bands.
And, even at a full wave of height (impractically high for all but a lucky few), a horizontal loop antenna has an inherently very high angle of radiation at the fundamental frequency. With a full-wave loop in free space, the most pronounced radiation is perpendicular to the plane of the loop. Combine this with ground effects from very low heights, and it is possible that most of the radiation emitted by the antenna will exceed the critical angle, the angle at which the radiation is no longer reflected off the ionosphere, but instead escapes into space. Most people who are enthusiastic about the performance of their 160m horizontal loop are actually referring mostly to the performance of the antenna on the higher bands, where the angle of radiation decreases as the pattern "flattens out."
In very, very general terms, with lots of exceptions, those who are lucky enough to get their 160 or 80m loops forty feet high or more report performance resembling a Near Vertical Incidence Skywave antenna, that is, good to reasonable performance for local and regional work, on the fundamental band and the first harmonic. On the other hand, many people who have had their loops strung at thirty feet or less are convinced a 160 or 80m horizontal loop is a worthless antenna on those frequencies, and will not hesitate to tell you so.
If you are interested in doing DX work on 160 or 80m, read up on specialized antenna types for those bands.
Meanwhile, if you haven't done so, spend some time listening for DX with your loop on 20 and 15m. If you find the antenna does not hear well on those bands either, you may have a problem somewhere. If, though, it seems to hear DX better than a dipole at the same height, at least in some directions, on 20m and up, it is probably working normally.
Thanks for the input, comments inline.
I wonder if i would be better off running this as a random wire, rather than a loop?
Originally Posted by WX7G
Yes, you're right I guess I expect you to read my mind:-)
Originally Posted by WB5YUZ
When I mention performance, this was specifically in relation to 80m and 160m. My main goal is "reliable" local performance (local traffic net, etc). I do have an existing OCF dipole at the same height, and it seems to perform better than the loop on 80 in all comparisons. I try the local 80m net regularly, and the OCF always seems to outperform. Certainly not much in the way of DX on these bands this time of year...and not expecting this low antenna to provide this function.
The loop DID seem to do better on some occasions on 20m as compared to the OCF for DX, so you make a good point.
Very much appreciate the comments.
If one wants a 1WL loop to radiate a figure-8 pattern like a dipole, it must be oriented vertically, not horizontally. Almost any wire antenna with a height of 25 ft. is going to be an NVIS antenna on 160m.
Originally Posted by VE4DDW
73, Cecil, www.w5dxp.com
The maximum power transfer theorem works just as well for a non-resonant antenna as it does for a resonant antenna.