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Post by lightfoot on Aug 3, 2010 14:56:18 GMT -5
My buddy has a 4 element Maco M104c on the Horizontal Plane.which was an upgrade from a M103c. 17 foot boom at 1 1/2 inch diameter boom. No SAGGING OR BENDING OF ANY KIND. Very Rigid actually. Coax being used is75 feet of lmr 400 on a 10 foot Rohn telescopic pole. Can not be put higher.Above ground its actually 35 feet. The Swr of the antenna is good about 1:1.2. Using an MFJ 259B. When Antenna starts to rotate East swr climbs as high as 1:1.9. Then eventually drops off again. There is nothing in the way when pointing East. But there is a building towards the back door reflector about 25 feet away. Antenna clears it regardless of it being 25 feet away. There are a few satellite dishes around and below the antennas area. Now if i tighten up the back door will this cure coupling from this building while the reflector is pointing towards that way. I know there are programs to optimize these beams.Any Idea would be great. Also Ive seened people mount the Gamma match upwards as opposed to hanging it down. Any benefit to doing this. Any Answer from our Antenna Gurus would be Great. Thank you and hope to hear some comments.......  |
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Post by cbrown on Aug 4, 2010 8:34:11 GMT -5
How close are the satellite dishes? Is the building 25 feet away from the center of the antenna or the end of it? I don't think the building 25 feet away is going to cause enough reflection to raise the SWR that much.
Still, you're below 2.0:1, which is about 11% loss. I normally like the SWR low, but anything 2.5:1 or lower isn't enough to loose sleep over. Unless you're running some large transistor amp.
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Post by Sniper..Unit 305 on Aug 4, 2010 10:10:22 GMT -5
lightfoot, At the SWR you are showing at 1.1.9 you are still darn near flat on the SWR and not quite exhibiting a 2% loss. I and probably most others would be thrilled to have an SWR that good without a tuner in-line. Leave it be and don't try to fix something that isn't broke. Heck with those SWR readings you could run whatever you wanted to run with no fear of problems. As far as moving the Gamma match from it's current factory position, I have no idea of what that would or would not do. I know I myself would not change a thing with that match. Sniper
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Post by lightfoot on Aug 4, 2010 13:20:50 GMT -5
Hey Guys thanks for the response. Thats great to get some feedback there. The swr is just a hair under 2. When its pointing east. Cbrown the building from the elements is 25 feet and we clear it up as well. Also Big Air condition units on that roof. The Satelite dishes are about 15 feet away from the beam. Thats measuring below and away. Sniper i meant to say just a hair below 2 when pointing east but when its turned towards the west it drops down real low. My buddy has a matcher in line and is able to maintain the swr that way. Running 350 watts also. Beam seems to work great but we just didnt like what we saw on the MFJ 259B. I got another MFJ 259b to just verify but saw the same results. Thanks again and hope to hear from you all again................
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Post by Sniper..Unit 305 on Aug 4, 2010 14:05:03 GMT -5
That clarified the SWR reading quite a bit. Now there is a difference between 1.1 to a 1.9 or very nearly a 2 even. Now I would say you are experiencing some type of problem when pointing to the east, but I sure would not think that what you have would be the problem. I would not think that either dish would interfere since they are below and away from the beam, nor the building. I can only go by how my situation is here and try to compare. I am located in a city and our building lots are only 40' wide and 110' deep. My Penetrator is mounted on one of my roof dormers on my house with my Astrobeam mounted on a tower at the back of the house at a height of 30' to the feed point. As you can see, my beam doesn't even clear my 3 story roof top, and points into my neighbors houses on the left and right of me, as well as only being 15' away from the ground elements of the Penetrator. I have a steel garage located not 10' away from the tower that holds the beam, and believe it or not....my swr is exactly the same in any direction that I point the beam, no change what so ever. Now that you see what a mess my set-up is, and how the swr doesn't change, you can see why I just really can't see how your situation is causing your swr to change, especially since you are horizontally mounted. I am curious to see if anyone comes up with something here on the forum for you. Sniper
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Post by lightfoot on Aug 4, 2010 15:02:33 GMT -5
Hi Sniper thanks for the come back. Man I was sure you would have tons of coupling especially with the steel garage not even 10 feet away. But sounds like you have it going on good. I have raised the beam up as well from the rotor from being on top of it to 2 feet and nothing..........Hahaha Im baffled. By the way the rotor being used is a yaesu G 450-A. At first i thought it was perhaps current being transfer from my rotor to my beam thats what led us to raise it further away from rotor but nothing. Hope we can get more input from some of our Antenna Gurus. Best regards and Sniper if you come up with something else please chime in..........Im curious to know.....
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Post by cbrown on Aug 5, 2010 9:14:24 GMT -5
I'd run it as is and don't worry about it.
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Post by Marc on Aug 23, 2010 15:07:49 GMT -5
When you are using the MFJ are you connected to the 75 foot of coax?
I am not to familiar with LM400 but does it have a single center conductor? Is it stiff like 9913?
As a test use a 17 feet 9 inch piece of RG8 from the ant to the LM400 using a barrel connector having the slack at the rotor being the RG-8 and see if it helps, just a thought.
Marc
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Post by cbrown on Aug 24, 2010 9:03:11 GMT -5
Times Microwave LMR-400 is stiff like the Belden 9913-F7, but I prefer the LMR-400. In hot area the 9913 will have problems with center conductor migration, usually from taping the coax too tight to the mast.
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Post by Marc on Aug 24, 2010 13:03:39 GMT -5
It can also migrate when used on a beam. The motion of twisting
can cause the dielectric to twist around the center conductor
causing a shift in the SWR due to impedance change.
I had that prob switched to 213 and cured the prob.
That is the test I wanted him to try.
9913 is fine on a GP but a beam for the average user 213 will due just fine.
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Post by cbrown on Aug 25, 2010 11:59:33 GMT -5
I myself prefer LMR-400 for the shielding.
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Post by lightfoot on Aug 31, 2010 17:22:16 GMT -5
Hey Sorry I strayed from my Thread. I actually used about 3 feet of regular RG8U coax with my Mfj259b to tune the beam. Its Low at 1.2. Its just when it starts turning due east it rises. Hi Marc Thats exactly what I did I spliced Rg8u with a barrel connector to my LMR400. Im currently using an antenna tuner to maintain Flat Match. Seems to work good. Just wish I didnt have to. Thanks Guys and best regards from the Coast of San Francisco......
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Post by lightfoot on Aug 31, 2010 17:28:08 GMT -5
Wondering if I raise her up 7 more feet will it make a difference, Hmmmmm Oh well Thanks again......
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Post by Marc on Aug 31, 2010 19:41:35 GMT -5
How far are your top guy wiers from the ant? Do they have insalators in them? do you have any comming due west off the back ? How far below the ant are they?
Just a thought. Any chance of some pic's
Marc
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