I have a 105CA at 125' and a 402CD at 115'. Both the computer and real world suggest that there is very little interaction at 10'. At 6' there is some interaction, but probably not enough to worry about... You'll lose about 1/2 DB of gain. 73 Bill ----------------------------------------------------- My opinion is that the antennas probably won't even see each other. Someone who has access to an antenna modeling program can give you more specific info. Since the 105 is the 4th harmonic, I don't think you'll have any problems. > > (2) What's the general consensus on pinning the booms to the mast? > What does this do to the integrity of the boom? mast? I wouldn't bother pinning the booms. First, it'll take you forever to drill through the VERY HARD mast. Secondly, antenna system rotation is due to mast slipping in rotato, NOT antennas on mast. The Hy-Gain boom-to-mast clamps will never slip. I would upgrade the Cushcraft plate to something more substantial. If you're still worried, add another U-bolt and saddle - more friction. I'm also not a big fan of pinning the mast to the rotator. Instead of the forces turning harmlessly, a pinned mast will find the next weak link in the chain and it's usually the gears or brake of the rotator. It's easier to re-align the mast than replace a busted rotator. 73 and good luck. Sounds like fun! Steve K7LXC ---------------------------------------------------------- Hi MAtt...I have Cushcraft 2el 40 at 160' and HG105 at 154' only 6 feet apart....maybe not the same the HiGain 40???? mine seems to work OK.....the 10 mtr antenna at that height is a BOMB !! 73 good luck...de John K9UWA ------------------------------------------------------------ We have been using a 40-2CD with a 10-4 above it for a couple of years now....seperated about 5 or 6 feet. It has been a rather successful combination! The antennas are modified mechanically only, their electrical designs are as per Cushcraft. The 40 beam has to its claim a #4 SS CW finish, and it looks like the 10 meter beam might have a #1 finish in the 10 meter contest. I would say don't worry about these two, based on my experience. If you wanna see what they look like check out my slide show at the Dayton contest forum this coming weekend. 73, Jim K1ZX k1zx@contesting.com ------------------------------------------------------------------- I use a 3 el 40 with a 105BA about 8' above it. The 40 meter beam is made from 402BA elements that have been extended slightly. It does use the same insulators and loading lines(now slightly shorter because the elements are longer) as the stock 402BA. I had to rotate the 105BA 90 degrees to the side to prevent interaction between the two. 40 was never bothered, but the SWR on the 105BA was too high and the SWR curve had a double dip in it. After the 90 degree turn, the 105BA dropped down to 1:1 at resonance and plays very well. One other thing, right after putting up the 105BA I had strange intermittent problems. Turned out the coaxial choke at the feedpoint was arcing to the boom at a point several turns back from the feed. Replaced it and it did it again. I finally put up another choke balun and insulated it from the boom with a piece of 3/8" thick plastic of unknown ancestry and that fixed it. Since I never heard of this happening before and I have used other 105BA's without any problems, I suspect this was also due to some interaction between the 40 and the 10, but I have no way of knowing exactly. Anyway, if you have any SWR or arcing problems you might want to swing that 10 at right angles and see if that cures your problems. Dan KL7Y ------------------------------------------------------------------------ I have my 105CA seven feet above my 40-2CD. (105CA @ 141ft, 40-2CD @ 134ft) No problems noted. Keeping the 105CA 15-16 feet away from (above) the 205CA is the HiGain spec. I'd worry more about the spacing of the 40-2CD and the 205CA, but modeling it will tell you the answer better than asking it here. I have little experience with the pinning of booms. I use the HiGain clamp on my 105CA, but I do not pin it to the 2 inch mast. Haven't had a bit of problems with it. The 155CA and 205CA I have are on ring rotors, so don't know what would happen on a mast. Bill, N3RR -------------------------------------------------------------- My opinion is Don't Pin. Let the mast slip in the rotator. I'd rather replace the coax pigtail than have to ship a bag of rotator parts to CATS... -Tony, K1KP, fisher@hp-and2.an.hp.com Modeling will tell you about the interaction of any antenna combination, as has been said. I had a 6el KLM 10m about 8' above a 6el KLM 15m on a Rohn 25G tower (48'). I did this before the days of modeling S/W. Worked great. Later, I modeling and saw there was a lot of interaction even at 20' of seperation. I couldn't have mounted things differently, but it worked. Moral, sometimes you have to compromise. What I really am sending this for is to advise you to symmetrize the booms of the antennas. By that, I mean to mount the booms in their physical center so there is an equal amount of boom fore and aft of the rotor mast. This will reduce the rotational stresses on the rotor to near zero. You can do this by adding a length of boom material on the "short" end. This will allow you to still mount the antenna at the CG but still at the physical center of the boom. This should eliminate the need to pin anything. I pinned the rotor mast of my 6el KLM 20m and 2el 40m array, and, as Steve (K7LXC) says, the forces found the next weak link (the output ring gear). When I fixed that (went from a cast gear to a solid steel one), the forces found the next weak link (the key on the ouput shaft). The solution is to reduce the rotational torque forces to near zero by symmetrizing the booms (or by getting the biggest rotor ever made!). I say near zero because the elements will introduce some torque because of their offset. There was a short article on this subject in the DX Magazine by Dick Weber, K5IU, of Rotating Tower Systems some time last year. This was a boiled down version of a more extension pair of articles he wrote in Communications Quarterly a number of years ago. If you would like the references, let me know. I will have to dig them out. Makes for very interesting reading. Hope this helps. Bob, W9UI.