Hi Skip, The numbers for the models seem very optimistic. Normal gain for J-pole (theoretical) can not be more than a dipole, since the antennas is an end fed dipole with the "Q" section for matching. This means at most 2.14 dBi, but maybe you are experiencing some ground gain which you can get on vertical too from my limited understanding?
When the CSVHFS does annual parking lot type tests each year and they seem to come up with higher numbers than the theoretical. That may be why KU4AB's halo antenna exceeds the theoretical maximum by quite a bit. And the take off angle is very important as you note. There are companies that make claims of very high gain numbers but they are not toward the horizon, HI. The nice thing about quads is that they are easier to match than yagis often requiring only a direct connection to the driven element since the other elements reduce the impedance closer to 50 ohms and away from the 100+ ohms of a single loop. Although a bit bulky, with a three dimensional form factor, it is less likely you will poke out your eye. You might remember the portable 2 meter quad that QST published in the early 1980's. The big 3 x 5/8 collinears may be able to reach just over 8 dBi, but it just is not enough for the longer reach. It is of course way better than a half wave J-pole. When you need over 12 dBi or more on one end, (vertical or horizontal), it is pretty hard to do better than a rotatable yagi. An important question to ask: If you need to operate on battery power, will you be able to rotate the base station antenna? Most would at least need AC generator power although an inverter used for short periods, might be possible. Four of the recent Cebik triple dipole arrays look like one of the ways to get the most gain for a stationary antenna. I have asked some antenna companies if they are considering making such an antenna, but no response. In our area, we have some hams with rotating twist type Cushcraft 10 element V and H switchable beams, smaller beams, and some with double 13 element vertically stacked. Interestingly, these are hams who are also more into public service and don't normally get involved in weak signal work. It is a tough call to decide which way to polarize since hardly anyone is going to have H with any mobile setup and you need to have mobile to base communications. NBEMS, which I support wholeheartedly since it is the only cross platform open source digital software program of this type, is not really that easy to use compared with some other systems. You do have to practice this on a regular basis to get hams comfortable with how it works. And the weak signal NBEMS, where there is no phone communication possible, is going to need some very savvy ops who also know where the other station is located on the dial. The only 144.144 signals on 2 meters in my area likely originate from my station. I may be able to get some others to try. One of our local hams unfortunately decided to buy a Yaesu FT-450 instead of an 857D/897D so even though he is on digital with some OJT with the two of us getting together earlier this week, no go on 2 meters. We did OK on 10 meters though. 73 for now, Rick, KV9U kh6ty wrote: > Rick, > > >> Skip, >> >> Realistically, the 5/8 wave will be maybe around the gain of a dipole. I >> would use 2 dBi, maybe 3 dBi at the most. I don't think there are any >> 5/8 wave verticals that can do much better than that and some antenna >> gurus point out that they can perform worse than half wave antennas. I >> have both quarter and 5/8 wave so I will try and do at least a "local" >> test. >> > > Please do! We need as many field tests as possible. > > This morning I did some modeling studies over real ground with the following > results: > > J-pole at 3m, 5.17 dBi at 6.2 degrees (vertical) > J-pole at 3m, 7.7dBi at 9.8 degrees (horizontal) > > 3 section 5/8 wave collinear at 3m, 6.67 dBi at 9 degrees (vertical) > > Single vertically stretched quad loop at 3m, 9.65 dBi at 9 degrees > (horizontal) > Single vertically stretched quad loop at 3m, 6.28 dBi at 7.8 degrees > (horizontal) > > Ground plane at 3m, 4.4 dBi at 46 degrees (vertical) > Ground plane gain at 9 degrees, -0.2 dBi. > > A 3 section, 5/8 wave, collinear is 12 feet tall. > A stretched quad loop is only 14" tall in comparison. Turnstiling two of > these (like a stretched "eggbeater" antenna, reduces the gain by 3 dB, > resulting in a horizontally-polarized antenna of 6.65 dBi gain, but with a 9 > degree takeoff angle, and omnidirectional coverage for mobile use. Compare > this to maybe 2.5 dBi for a single 5/8 wave whip (unknown takeoff angle, but > somewhere between 46 degrees and 9 degrees). The big problem with any > shortened vertical whip is that too much of the energy is radiated at a high > angle. The takeoff angle probably accounts for a significant part of the 6 > dB disadvantage of low vertical antennas that we have found during actual > field tests. The three section 5/8 wave collinear gets its gain by > compressing the high angle radiation, but it takes three 5/8 wave sections > just to get the takeoff angle down to 9 degrees. The study with the J-pole > rotated horizontally was only for comparison and it not a practical > solution. > > The total antenna gain for us to reach 70 miles in flat country was 16 dBi. > If an EOC is using a three-section collinear at 30 feet for omnidirectional > coverage, and a mobile is using at best a 3 dBi antenna, the total available > gain is only 6.7 + 3 dBi = 9.7 dBi, or a huge 6 dB short of the gain that we > had but is omnidirectional. > > The higher gain horizontally-polarized setup is an EOC with four stacked > "Big Wheels", for about 9 dBi of gain and an "eggbeater" style, stretched > loop, mobile antenna of 6.6 dBi of gain, for a total system antenna gain of > 15.6 dBi, and still have a low takeoff angle. This puts the burden on the > EOC to have a high, tall antenna, which may not always be practical, so the > alternative is to make up the necessary gain on the portable end by using a > higher gain quad that can be broken down to fit in the trunk of a car. I > have developed three designs - a two element quad that is only 13" thick and > does not have to be broken down, and 3 and 4 element quads that can be and > reassembled on site. The 4-element quad has 12 dBi of gain if needed to > reach an EOC. > > >> We must not loose sight of the fact that almost no hams have horizontal >> polarization and almost all have do have vertical polarization. >> > > This again begs the question as to how many have ROTATABLE vertically > polarized GAIN antennas. Most I have talked to do not have a rotator. > Instead they use multielement vertical collinears. Those that do use yagi's > generally have them fixed in direction and pointed at a favorite repeater. > None of these installations are going to get much range without a repeater > and a way to rotate a yagi. > > >> And weak >> signal hams do not tend to focus on public service activities so you may >> not have any stations that you can work. I don't know of anyone who has >> any interest in my area. I would suggest that hams ask their weak signal >> operators whether or not they would be willing to participate in this. >> It takes a LOT of practice to make this work. You may not get it to work >> at the time you most need it. >> > > The good thing about the NBEMS concept is that in a pinch ANY ham receiving > an emcomm CQ can forward the messages to any EOC with Internet connectivity, > phone service or cell phone service. This intermediate station does not have > to have emcomm training. He is simply a relay station to the EOC. Takes very > little practice as the software is very simple. > >> Since voice communication is not going to be used (too weak a signal) >> for many of these digital transfers, you would need to set up a specific >> frequency and offset. I have been monitoring and sending on 144.144 as >> suggested by others, but have never heard anything. But that is mostly >> on vertical polarization for now. >> > > With vertical polarization, you are 20 dB down from using horizontal > polarization, so you will not hear anything. Anyway, currently, there is not > much PSK31 activity on 144.144 and probably none in range of your station, > even if you have a horizontally-polarized yagi. > > >> The period transmission is very clever, something like Patrick, F6CTE's >> Multipsk programs sending of repeated characters. You could just have a >> macro set with the repeating character, and you probably do this. >> > > Actually, I use a macro or just send a file with fldigi. My 2m PSK31 beacon > uses a chip programmed to send the beacon message, which is 50 periods plus > my callsign and grid square. I use it almost daily for comparing antennas. > > 73, Skip KH6TY > NBEMS Development Team > > > ------------------------------------ > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/sked > > > > Yahoo! Groups Links > > > > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - http://www.avg.com > Version: 8.0.176 / Virus Database: 270.9.11/1817 - Release Date: 11/28/2008 > 8:17 AM > >
