Mike: I apologize if my query came across as an insult!! Mea culpa sent from out here in the black hole of 160 meter communications - s/w Utah. I think I said I wasn't doubting your claim and I wasn't questioning your "conclusions" - just attempting to find some modeling or Measures of Performance to substantiate it as, lately, I have been seeing/reading of anecdotal "evidence" and I, for one, am interested in supporting data/measurements. I use/employ a 43' vertical on 160 through 17 but can't compare it to a 1/4 wave over the same radial field -- certainly your closeness to the water may "answer" or provide a reason for your success with a 5/8 over 1/4 so, with the modeling info I supplied perhaps someone who knows the modeling apps(s) could do some "investigating" in the form of modeling to answer that?!?~! OK?? 72, Jim R. K9JWV
> From: [email protected] > Date: Sun, 8 Sep 2013 07:18:18 -0700 > To: [email protected] > CC: [email protected]; [email protected] > Subject: Re: Topband: 5/8 wavelength vertical is mo betta than shorter > versions?? > > Tom (and James), > I am well aware that my comments concerning the 5/8ths wave was based upon > subjective/anecdotal evidence. I am in a science (Astrophysics) by > profession..... I do know the difference. HOWEVER, I cannot completely throw > out the simple fact that when I altered my 20 meter omni antenna for Winlink > to the 5/8ths, that I received UNSOLICITED comments from the system users > stating (100 percent of them) that my signal was much improved into the areas > they happened to be sailing. None of those people, not a single one, knew > that I was changing my antenna. The purpose being just that..... to see if > anyone complained or said anything else concerning performance from THEIR > point of view. In reality, THAT is the point when supplying a service..... > What do the USERS think of the performance, not what I think or what a FS > meter says. > > Even if I had the equipment to measure the performance and the equipment says > that my signal should be improved, but the Winlink user comes online and > universally states my signal sucks, I will REMOVE that antenna. I know that > isn't likely, but if the modelling software states the signals should be > worse and they are, 100 percent, reported as improved, then there is > something at play that the modelling software isn't taking into > account........ > > Not arguing, just answering that initial question that from my EXPERIENCE > with that antenna, it works better than the quarter wave at the same > locations I happen to be...... AND ONLY ON 20 meters. I won't speak to any > other band, although I would think it would work there, too, because I have > not put one up for those other bands. > > As an aside, alot of folks are using that so-called non-resonant vertical > antenna that is roughly 43 feet tall....... They seem to be having some > success with them on the bands. Physically, they are pretty convenient..... > and on 20 meters, they happen to perform pretty well, judging from user > comments, anyway..... and at that band, it is roughly 5/8 wave in electrical > height. So, again, I find it interesting that actual experience argues with > the modelling software (in MY particular instance). But, again, in my case > IN HAWAII, I had an outstanding location that, for some reason I don't know, > happened to favor the 5/8 by alot more than even the theoretical gain would > indicate. NOBODY would comment, much less 100 percent of commentors, on a > slight gain of 2 db. Heck, that wouldn't be worth the effort. However, I > think you are quite right, Tom..... something else is at play.... ground > clutter (I had some.... loads of tropical trees and plants in the area), some > significa nt > ly tall sailboat masts RIGHT ACROSS THE STREET from my house (very close), > etc, etc. Then you consider the seawater ground that was so close by...... > There are many factors to take into account, not much of which does a > modelling software take into account. Undoubtedly the answer is there and > not directly related to antenna gain. I did try elevating it on top of a 40 > foot pipe mast and using 8 resonant radials....... it made no difference > except to increase the chances that high winds would knock it down. In terms > of SUBJECTIVE performance and comments, no difference. So, I put it back on > the ground and carried on. > > Remembering what the antenna was for, and where it was located, putting up a > horizontal 80 or 90 feet in height simply wasn't possible. The SERVICE I was > providing required OMNI directional capability, so even a dipole would be > unsat in at least 2 directions...... those being the directions an emergency > call would not be heard...... Not a good situation for the given purpose, > right? > > I will say that I didn't appreciate the comment concerning how I came to my > conclusions about antenna performance. Insults only prove that one has run > out of reasonable arguments..... and that is ALL it proves. Given that, this > will be my last post here and I am likely removing myself from the list. > Insults are NEVER science...... not now, not ever! > > Mike AB7ZU > > Kuhi no ka lima, hele no ka maka > > On Sep 7, 2013, at 18:59, "Tom W8JI" <[email protected]> wrote: > > >> The above modeling results just don't support that contention/posit so I'm > >> wondering what else comes in to play that could lead folks to love the 5/8 > >> wavelength vertical over a shorter version, regardless of frequency? I > >> don't see one performance comparison that supports that claim. I'm not > >> saying the "claiming person" isn't correct but....I don't see how! > >> Help - what am I missing here? > >> 72, Jim Rodenkirch K9JWV > > > > The 5/8th wave obtains the small amount of gain it has through effects of > > ground reflection. The current maximum is elevated, and that elevation > > causes additional phase shift with the illumination of earth out some > > distance from the antenna. The re-radiation of earth is sometimes explained > > by an "image antenna". The image antenna is a fictitious antenna directly > > below the real antenna, and this "image antenna" simply represents what the > > earth at a distance does from the illumination from the main antenna. > > > > The 5/8th wave moves the current maximum slightly higher than a quarter > > wave above earth, so the fictitious image moves slightly lower than a 1/4 > > wave below surface. > > > > If you move the 5/8th wave above earth, such as in a groundplane well above > > the earth, the extra length no longer provides gain. Instead, it actually > > reduces gain at low angles. > > > > Another effect is the extra height above ground of the high current area > > can help get the antenna's main radiating area a little bit higher above > > ground clutter. > > > > This would also apply to an extended double zepp, where the second antenna > > half makes the image unnecessary. Each half of the double zepp is the image > > of the other side, so we don't need earth. > > > > So it is a very specific benefit from the 5/8th wave caused by moving the > > current height up above a reflecting surface, or in the case of a double > > zepp moving current away from a second identical element while still having > > a common center feedpoint. > > > > One of the biggest antenna hoaxes played on people was the 5/8th wave CB > > groundplane antenna. Two meter 5/8th wave groundplanes are the same. The > > work on the broadcast band to increase groundwave signal because soil is > > often reasonably low loss on the AM BCB. If the soil out some distance from > > the antenna is lossy, or if it does not exist, the 5/8th length causes > > increased low angle loss. > > > > This is why when you look at models, outside of specific cases like some > > cases of low broadcast band use, we have a tough time seeing the gain > > imagined or claimed. A field strength meter has an equally difficult time. > > :) > > > > 73 Tom > > _________________ > > Topband Reflector > _________________ > Topband Reflector _________________ Topband Reflector
