Tuning on the ground first - Elmers Forum at eHam.net

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eHam.net Forum : Elmers : Tuning on the ground first

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Tuning on the ground first	Reply
by VA3SLJ on March 14, 2004	Mail this to a friend!
I am installing a Valor Pro AM AB5 antenna on my roof. This antenna is designed for mobile use, and is in the "spider configuration:" the resonators for 10, 15 & 20 meters are horizontal, 40 OR 80 is vertical. For each band I have cut 2 radials at the proper length, so I will wind up with 10 wires draped over my roof and dormers. The mast will attach to an unused chimney on the third floor of my house, and so the antenna will finally be about 40' up. Is it possible to set the mast on a tripod in my yard, spread the radials out on the ground, and tune it there before installing it on the chimney? I can access the top floor from a balcony, but I will still need to to bring it down for each adjustment, something that will take quite a lot of time. I know that the antenna can work from the ground as I described, but I wonder if I would still need to retune after it's on the roof. The radials will be spread differently upon the roof, and there is the elevation difference to consider. In either installation I will ground it to an 8' copperclad rod. I guess my question boils down to the effect of antenna height and radial placement on the final tuning of the antenna. Any help/advice/warnings will be much appreciated. Scott VA3SLJ

RE: Tuning on the ground first	Reply
by KD5PVM on March 14, 2004	Mail this to a friend!
Scott, I too have a Hamstick mounted at home on a mast, not on a vehichle. I found that the swr did change enough from ground level to operation level that I did need to adjust it slightly. I have a hamstick dipole and it was the same procedure. Both could've worked but I guess I wanted to see if I could get the swr better, so I took the extra time and got them a bit lower. One last example. I got a Butternut HF2V and set it in the tripod I was going to use on the roof, but checked it first on the ground. Again, I had to do a bit of tweaking. Hope that helps. Good luck. Alan kd5pvm

RE: Tuning on the ground first	Reply
by AG4RQ on March 14, 2004	Mail this to a friend!
Any antenna should be tuned where it is intended to be mounted. SWR will almost always be different if an antenna is moved and remounted. The antenna needs to be tuned once it is mounted on your roof. I suggest that you get another ham to help you with it. One of you needs to be on the roof tuning, while the other is at the radio keying it and checking SWR. For goodness sake, key the radio with the lowest power necessary to register on your SWR meter. We don't need any "cooked hams"! You can communicate using a couple of HTs.

RE: Tuning on the ground first	Reply
by AA4PB on March 14, 2004	Mail this to a friend!
If you want the absolute best SWR you'll have to do it with the antenna in its final location. However, I've always found the SWR to be quite reasonable with 3-band yagis, shortened (Hamstick) dipoles, 6M, and 2M yagis after tuning it near the ground (where I could reach it with a step ladder - 12 feet perhaps). I did some tests with a 40M portable Hamstick dipole and found that once the height was up to 10-feet the SWR didn't change much with increased height.

RE: Tuning on the ground first	Reply
by WB4QNG on March 14, 2004	Mail this to a friend!
I am like the rest of the guys. You will need to retune when you get it up but go ahead and tune them on the ground they should be close.

RE: Tuning on the ground first	Reply
by K3UD on March 14, 2004	Mail this to a friend!
Why not just ground mount it and bury the radial system? it would be much easier to tune to resonance and you would not have wires draped over the roof and hanging off it. I did this with a 75 meter hamstick and 8 30 ft radials on the ground, and it worked out rather well, much better than it performed as a mobile antenna on that band. 73 George K3UD

RE: Tuning on the ground first	Reply
by RobertKoernerExAE7G on March 15, 2004	Mail this to a friend!
If your coaxial feed line is rather short, you may not have to bother tuning at all. Bob

RE: Tuning on the ground first	Reply
by VA3SLJ on March 16, 2004	Mail this to a friend!
Thanks, all for your answers. Based on your replys, I will plan to do the following: 1) tune it on the ground 2) make notes of the differences in SWR readings when I get it on the roof 3) retune. One reason I want to tune it on the ground is so that it is at least "close" as one of you suggested, and, if I really like the antenna, I might buy one to use as a portable field antenna. I would at least, then, know what to expect. One of you suggested leaving it on the ground. I would consider this, except I am in an inner-city lot, which means a really big house with a tiny yard; a yard my wife has envisioned being "wireless." By the way, the coax run will be about 100 feet, if that matters. It is 50' from the shack to the back of the house, then 50' up and over to the other corner. I am feeding it with RG8U. Thanks again for all the help. I'll try to post a review when I get it going. Scott VA3SLJ

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