Hi Rick, > > 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?
Yes, "ground gain" is mostly responsible for the higher gain figures. The J-pole in free space has a modeled gain of 2.34 dBi at 10.2 degrees, very close to the isotropic dipole value of 2.2 dBi, or 2.14 dBi. However, over real ground, 10 feet up, the gain increases to 5.17 dBi at 6.2 degrees. Flipping it horizontally, the gain increases to 7.81 dBi at 9.7 degrees, but for a better comparison, the gain horizontally is 6 dBi at 6 degrees and 10 feet. Mounted on a car at 5 feet, the takeoff angle increases to 19.1 degrees and the gain at 6 degrees is only 1.2 dBi horizontally. Rotated back to vertical at 5 feet, the gain is 4 dBi at 8 degrees, or 3 dBi at 6 degrees. In comparison, the square quad loop has 9.21 dBi of gain at 14 degrees, or 5.3 dBi at 6 degrees. So, in an apples-to-apples comparison, the single quad loop still excels the J-pole by 3 dB, which appears to be what we are finding, instead of the 6 dB difference previously noted, which did not normalize everything to a 6 degree takeoff angle. > > 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. I have a KU4AB "square loop" - in fact I started on 2m with a stacked pair. Comparing it to a dipole on my beacon, I find that the pattern has serious nulls, especially in the back (-6 dB!), and is just not omnidirectional. I tracked NK4Q across the center of South Carolina comparing the KU4AB loop to a single stretched quad loop (facing me) and there were many times that he could not even copy me on the KU4AB loop when copy was perfect on the stretched quad loop. A true "halo" works much better. > > 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. For portable use, my OptimizedQuad (two stretched rectangles in a diamond configuration) in a driven element/reflector arrangement, is probably a good compromise. It is only 20" x 20" x 13", so will fit in a trunk and does not have to be reassembled in the field - only put it up on a portable mast as high as is practical. If that gain (8.2 dBi at 6 degrees over real ground) is not enough for the distance or terrain, I also have a 4-element quad design with 14 dBi of gain (over read ground) at 6 degrees at 10 feet which can be "unplugged" and also fit in a trunk. > > 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. Good point! The 4-element quad beam with its 5 foot boom fills that bill nicely and is easy to set up! The beamwidth is a wide 60 degrees, so it can be just pointed by hand in the general direction of the EOC and does not need a rotator. In a true field situation, the antenna will probably never be out of reach, so it can be turned by the "arnstrong" method. > > 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. Are you talking about his "horizontal polling array" paper? That was written because I asked him if he could find out what spacing I needed between 3-element quad antennas placed around a circle, but he did the article using moxon rectangles. > > 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. If you already have mobile to base communications, then you do not need horizontal polarization, but if you do not (because the distance is too far), then you need the extra 3 dB or greater that horizontal polarization brings to the table. > > 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. We start with PSK31 so it stands out against the noise, tune in the station, and switch to DominoEx. It works just as well, or better, to use the "Tune" mode of fldigi, tune that signal in, and then switch to DominoEx. > > 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. With NBEMS, we are looking for the most consistent, reliable messaging communications possible, and 2 meters seems to be the only band that can provide that. Otherwise, we use NVIS antennas and have to deal with the static and time-dependent propagation on HF. Weeks of tests on 80m and 40m this past summer showed that HF is a reasonable compromise, especially since the MFSK modes in fldigi have been modified to handle extreme static quite well. You might want to test HF in your hilly terrain and see how it works out, but be sure to use NVIS antennas at both ends. Although more trouble to set up than a 2m quad, I can imagine one end of a 130 foot wire attached to a building and the other end to a mast on a car trailer hitch or a mast on a plate mount so that the car tire holds in place as one way to get a NVIS antenna. At least the antenna does not need to be high for NVIS. I think we have beat the horizontal vs vertical polarization issue to death now, and need to proceed with additional tests to find out what range can be expected. SSB provides the greatest range, but the number of transceivers in the field with 2m SSB is limited. Horizontal polarization provides the greatest range, but the number of horizontally-polarized antennas in the field is limited, and many of the vertical yagi's in use do not have rotators. If we are going to limit ourselves to existing FM transceivers and existing verticals or yagi's, then we are probably going to need a repeater, because you can only stand so much degredation of S/N over SSB and horizontal antennas before you can no longer communicate point-to-point. 3 dB of gain on VHF makes a huge difference! That is why weak signal ops go to the expense and trouble of putting up two stacked yagi's instead of just one. FM costs 3 dB or more in S/N over SSB, and vertical polarization cost another 3 dB in S/N over horizontal polarization, so it is not too long before you cannot communicate at all point-to-point at with the EOC, except only over 15 to 20 miles. Once again, "there is no free lunch"! 73, Skip KH6TY NBEMS Development Team
