| Author |
Message |
    
Ohiobiker
| | Posted on Wednesday, December 18, 2002 - 6:41 pm: | 
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I just recieved my SmokinGunn-II today. After reading the instructions several times I fully understand how to assembly them...But here is my question??? It says to set SWR on Gamma's before they're put in the air, Now do I need to use the same pieces of coax that I will use once in the air or may I use shorter length's to set the gamma match's making it easier to do? Or must I use the length in which they will be run on from the shack once their in the air? It makes no recomendations as to coax length in the instructions. I am planning on using Anttron Micro-8 coax which is rated at 1K-watts, I have used this coax for years with no problems with power as I don't run that much power anyhow! I want to do this once and once only due to the cold weather in Southern Ohio. ****Bruce**** what is your opinion on this matter?...All answers will be greatly welcome. I will be putting this up after the 1st of the year if weather is right, if weather isn't agreable...I'll hire someone to do it for me...LOL....Thanks and Merry Christmas to all...Take time to remember the "Reason for the Season" |
bruce
| | Posted on Wednesday, December 18, 2002 - 8:46 pm: |
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crazy as it sounds if you can point it UP in the air it would help as for coax USE GOOD COAX NEW COAX! i never tell people to use old coax bad investment. AS for length any lengh will work as long as the antenna is tunned. You should be able to get very close on the tunning with anything over 50 foot. This is a 2 elm beam i looked at it and it should run 4-5 DBD ( 7-8 DBI ) so expect a solid s unit gain. |
Ohiobiker
| | Posted on Wednesday, December 18, 2002 - 10:14 pm: |
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Thanks Bruce and yes when I mentioned the coax I meant the brand of coax not that I was planning on using any old stuff. Just that that kind is local for me to buy direct from the company. I always use new coax on anything I do or attempt. I think I might be able to try to point it stright up. will keep you posted, but as I said it maybe after the 1st of the year before it is in the air on the tower. Thanks again |
Tech808
| | Posted on Wednesday, December 18, 2002 - 10:31 pm: |
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Ohiobiker,
Completely assemble antenna with the coax you are going to use connected to the antenna.
Set antenna on 6 foot step ladder.
Set SWR then raise antenna and mount and you are all set.
Lon
Tech808 |
bruce
| | Posted on Thursday, December 19, 2002 - 5:08 am: |
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Lon would the lobe be tight enough that the 6 foot highth would be enough ?? i know frount to side should be fairly high My beams were all at VHF/UHF so hight was not a problem.
Bruce |
Tech808
| | Posted on Thursday, December 19, 2002 - 8:54 am: |
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bruce,
When I put my 3+3 Gunns up, the ladder worked great for setting SWR for me. Got H & V set at 1.1 and it never changed over the years.
Wind Survival has been great.
BUT! BIG CROW survival has broken three arm's off right at end of fiberglass inserts.
Took them down to repair and doubt they will go back up.
Lon
Tech808 |
bruce
| | Posted on Thursday, December 19, 2002 - 11:28 am: |
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OK i wasnt sure if ground reflection would mess things up .... it's not a problem at 1296! |
Marconi
| | Posted on Friday, December 20, 2002 - 2:53 am: |
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Ohiobiker, I am not too sure this will be quite as simple as 808 suggest. So, I give my opinion for your consideration.
Unless you tune at installed height, I really doubt there is such a thing as; “I want to do this once and once only.” If you tune near the ground look for something to change as you go up. A lot depends on the location.
JG probably gives the tuning advice they do for convenience and safety. The driven element doesn’t know if the antenna is pointing straight up or straight down, or if the boom is horizontal to the earth. The height of the driven element relative to the earth beneth it is what affects the changes noted in the tune.
The antenna tune may react to anything that is close enough in any direction. In your case, if you cannot get the back of the reflector several feet above the ground, then pointing up will place the driven element even closer to the earth than JG suggest and that will likely have an even greater affect on your tuning results.
This is not a complicated antenna having only two elements, but I do not recommend tuning with your working lines. Tune at the feed point if possible. Get as high as possible to do that, if you cannot tune at installed height. I think you will find this procedure far more accurate. Then your random lines should work just fine, assuming the tune is right.
When I use an SWR meter I use a handheld transmitter with a good 4+ watt output. I prefer to tune using a resonant 1/2 wave line, cut for the frequency of choice. You can check this out. Just check the tuning with several lengths of cable. If you see no changes in results, then use the working lines to tune.
JG also notes that both lines must be attached in order to tune the antenna correctly and even gives a caution, but I wonder about that. I know the vertical element reacts more to earth than the horizontal side, but I do not understand why JG notes to tune the vertical first. I would follow their advise however or maybe check it out if I had the chance. I just don't get either point because you do not change the physical layout of the antenna when trying to find a matching point on the element with the gamma.
I assume that JG cuts these antennas for the middle of 11 meters. If you wish to tune at another frequency very far away from the center of 11 meters, then you will likely have to operate with less than true resonance at the center of your frequency range, because the element lengths are fixed. The spacing is also fixed.
The antenna should show a good 2000 kHz bandwidth so that may not be problem for you if you tune within 11 meters. One thing to watch for in the bandwidth curve is balance and smoothness above and below resonance.
JG Star type antennas do not seem to show a very good rejection response. You may also notice some overall non-responsiveness after installing. Give it a few weeks, like JG suggests. Don’t get too upset, this is normal.
JG’s seem to talk very well and maybe you can live without a big rejection at your location. A two element is not going to show a huge front to back anyway, but it should be noticeable as you rotate. You may notice little difference when switching polarity also. This may be due to the angle of the horizontal element not being perfectly flat to the earth.
You may not have any problems just taking the simple route, but I notice you prefer to work a little higher in frequency, out of band. There are several of these Star type antennas near me, and they all had some problems with tune after going up. I hear them and to me they respond as though they were omni-directional when they turn. That is not my preferance in a beam, but it might be JG's design goals for max gain.
Concerning the problem with wind that 808 mentions. That is a problem when using bolts or sheet metal screws in aluminum tubing. The holes create weak spots near the flex points. I bet if 808 would check, he might find that the breaks split at the holes. This is very common in antenna failure. The JG’s are very heavy and well built, so I would not worry about that unless you have heavy sustained winds in your area. I prefer slotted elements using hose clamps myself. They tend to be more secure and make much better electrical connections.
I noticed that you have a 4 element beam. Why the change?
Hey Bruce, I assume your comment about 1296 suggest that you are at 1296' above sea level. I disagree with your suggestion, because it is the earth under your antenna that is at play when tuning.
808, if you have a Star type JG, then how have you found your rejection to be? Since you got such a good match, do you think JG cuts these antennas for the middle of 11 meters and is that where you tuned your 3+3?
Marconi |
bruce
| | Posted on Friday, December 20, 2002 - 11:04 am: |
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I WISH i was 1296 foot up i live in florida the highest point in the state is 300 foot LOL. No i worked on 1296 MHZ with quad stacked 20 elm beams at 40 foot and since a wavelengh at thoes frequencys less that a foot 40 foot is 40 waves above ground! Even at 6 meters 36 foot is a wave so i just wondered if you realy could tune a beam at 6 foot up?
Bruce |
Marconi
| | Posted on Friday, December 20, 2002 - 11:31 am: |
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Well Bruce I just looked in on the Christmas thread and noted that you are in Florida. My assumption about your 1296 comment was no doubt wrong. I guess you meant a tower of some sort. How is it up there?
Marconi |
bruce
| | Posted on Friday, December 20, 2002 - 1:26 pm: |
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marconi
LOL LOL a 1296 foot tower here 3 miles from the gulf of Mexico would allow me to see TEXAS on a clear day ! Heck i wonder if the county building people would mind it ........ RIGHT! |
CM 3885
| | Posted on Friday, December 20, 2002 - 2:18 pm: |
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The idea of using a handheld to tune the antenna works VERY well in my case.... |
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