Like Tom said earlier, it's all about ground loss. Near the sea, a 1/2 or 5/8 wave vertical may perform very differently than a duplicate antenna a long way from the sea. The near-field and far-field losses at the lower angles would be much lower.
73, Mike www.w0btu.com On Fri, Sep 6, 2013 at 7:04 PM, Bob K6UJ <[email protected]> wrote: > Mike, > > Tom, W8JI has a comparison between 1/4 wave and 5/8 wave vertical mobile > antennas here: http://www.w8ji.com/VHF%20mobile%20vertical.htm > He is comparing mobile antennas but it looks like the 5/8 wave can be 2 db > better than the 1/4 wave. > Looking at the radiation angle graphs it shows the 5/8 has more gain at > lower radiation angles in particular. > If you were doing your comparison on long haul contacts it makes sense > that the 5/8 would do better. > > Bob > K6UJ > > > > On Sep 6, 2013, at 4:35 PM, Mike Armstrong wrote: > > > Guy, you aren't reading my emails...... because that question is not > appropriate to the conversation. I am NOT, I repeat NOT talking the > difference between LOCATIONS, but the difference between ANTENNAS AT THE > SAME LOCATION! I am NOT talking about RURAL ANYTHING. That location being > on Gannet Avenue across from the Marina that was LITERALLY across the > street from my house. > > > > I say again, READ MY EMAIL as your question has absolutely NOTHING to do > with the conversation. The fact that you sent the same email to me after I > answered you tells me that you are not reading what I wrote. I am not > being insulting, but if you don't read ALL of what I wrote, you cannot > possibly ask a valid question or make any statements about its content. If > you read it, you would know that I am not saying ANYTHING about location > changes or differences. OF COURSE a sea water location is better than a > rural location. THAT fact has nothing to do with the comparisons I am > making or asking Tom to discuss. Sorry for the repetition, but I want to > make sure that you will see that, even if you don't read this email > entirely. Again, no insult intended, but it is tiring trying to respond to > someone who isn't reading ALL of what I wrote and jumping to incorrect > conclusions as a result. I WILL tell you the address, if you still want to > know, after you have read and responded > to > > the content of this email specifically. > > > > Mike AB7ZU > > > > Kuhi no ka lima, hele no ka maka > > > > On Sep 6, 2013, at 13:38, Guy Olinger K2AV <[email protected]> > wrote: > > > >> Mike, could you kindly supply the address on Iroquois Point? If it's in > >> the area I'm looking at with Google Earth, the answer why the > difference is > >> pretty plain, and points to why such a difference vs. a 160m vertical on > >> rural terra firma. > >> > >> 73, Guy. > >> > >> > >> On Fri, Sep 6, 2013 at 1:30 PM, Mike Armstrong <[email protected]> > wrote: > >> > >>> Oh, I didn't address one comment you made, Tom...... 5/8ths are dogs on > >>> 160? Really? That is odd in the extreme to me. I had incredible > success > >>> with a ground mounted 5/8 on 20 meters while I was stationed in > Hawaii. I > >>> was rather space limited, so I could only go up and a tower mounted > beam > >>> was a "no fly zone" in that particular situation. So, I decided to > try the > >>> 5/8ths wave vertical and its performance was nothing short of > spectacular > >>> when compared to a 1/4 under the same circumstances. Not to malign the > >>> simple 1/4 wave, but the 5/8ths performance improvement went way beyond > >>> what I would have expected...... and my expectations were certainly > >>> reasonable. My thinking was that lifting the major current node a bit > >>> above ground would probably be an improvement and, to my surprise, > that was > >>> an understatement in the extreme. > >>> > >>> I wouldn't want to overblow the results, but I simply couldn't believe > how > >>> well the antenna performed on 20. To be sure, I was on Oahu out in > >>> Iroquois Point housing, which is well situated with regard to the sea > (you > >>> are basically ON the water in almost all directions). Additionally, I > had > >>> 60 radials underneath the thing, spread evenly around the base (in > straight > >>> lines, no bending). So it was definitely an ideal vertical location. > But > >>> the difference between it and the quarter wave was what truly > surprised me > >>> (with all else being the same.... sea water location, number and > length of > >>> radials, etc). To hear that it doesn't translate to 160 is really a > >>> surprise to me...... Tell me more, assuming you did any kind of study > into > >>> why it didn't seem to work well. I am as interested in why something > >>> DIDN'T work as I am in why it does..... If for no other reason than to > save > >>> a few bucks and alot of time.... LOL > >>> > >>> Mike AB7ZU > >>> > >>> Kuhi no ka lima, hele no ka maka > >>> > >>> On Sep 6, 2013, at 9:25, "Tom W8JI" <[email protected]> wrote: > >>> > >>>>> Fully understood. I wasn't referring to the usual collinear antennas > >>> sold by "comet" or anything of that nature. I am referring to the > stacking > >>> arrangements used for ops like moonbounce, etc. As far as the design > >>> theory (and practical application) goes, I have a reasonable amount of > >>> schooling and experience (been active since 1966..... he he he). Just > so > >>> you realize I am not referring to the often (always?) false gain claims > >>> made by manufacturers for their antenna designs. > >>>> > >>>> ........but this is verticals, and not a narrow BW like a long Yagi. > The > >>> narrower the pattern of a cell in the stack, the wider minimum useful > >>> stacking distance becomes. > >>>> > >>>> Also, for 160, antennas are near earth. Earth spoils everything. A 160 > >>> antenna at 260 feet is like a two meter antenna at 3.25 feet above > ground. > >>>> > >>>> > >>>>> All I was saying was, "yes, it is possible and is done" when speaking > >>> to vertical stacking. As far as stacking what we would call "ground > plane" > >>> antennas (quarter wave vertical element against elevated radials), the > only > >>> example I have seen with any regularity is done aboard some Naval > vessels > >>> (stacked/phased, if you will, horizontally on a yard arm). I "think" I > have > >>> seen the same thing at airports, but I cannot tell for certain that > they > >>> are phased arrays or just happen to "look" like they are related. > >>> Understand that in all cases to which I refer, including my own, I am > >>> speaking of phased arrays, which I believe is what we are talking > about as > >>> well. I may have misinterpreted the question to some degree. > >>>> > >>>> This is 160. The distance ratio for the same behavior on two meters is > >>> 80:1. If we look at: > http://www.w8ji.com/stacking_broadside_collinear.htm > >>>> > >>>> we see **freespace** short dipole stacking distances, between current > >>> maximums, is 0.35 WL for 1 dB stacking gain. This is for freespace. > That > >>> means the current maximums have to be .35*160 = 56 meters apart **if** > the > >>> elements are in freespace. They have to be even further apart if near > >>> earth, because the earth reflection already compresses the vertical > >>> pattern. I'd guess, for 1 dB stacking gain over a ground mounted > vertical > >>> (ignoring ground losses), we could move the lower current maximum to > about > >>> 50 meters above earth and eliminate the upper element. That would > pretty > >>> much be a vertical dipole. If we wanted to get 2-3 dB gain, we'd > probably > >>> need 300 feet of height and an inverted groundplane at the top. > >>>> > >>>> For 160, is it is a useless endeavor at normal heights. > >>>> > >>>> Making matters worse, 5/8th wave verticals are dogs on 160. Been > there, > >>> done that, used them. A 1/4 wave vertical, or something up to maybe 200 > >>> feet, is actually better. They have never worked well here, they never > >>> worked when I used broadcast towers, and when W8LT used them in 160 > >>> contests they were also pretty weak. > >>>> > >>>> The whole thing is a waste of time on 160. Even if someone could run a > >>> vertical collinear with useful gain, it would just kill their signal by > >>> focusing it at too low an angle for 160, while nulling more useful > angles. > >>>> > >>>> 73 Tom > >>> _________________ > >>> Topband Reflector > >> _________________ > >> Topband Reflector > > _________________ > > Topband Reflector > > _________________ > Topband Reflector > _________________ Topband Reflector
