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454
New member
Username: 454
Post Number: 1
Registered: 11-2016
| | Posted on Tuesday, November 15, 2016 - 10:49 am: | 
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Firstly, I did look at previous post to find my answer, but did not find what I was looking for in regard to a direct answer to my questions. I am using a Sirio 827 Omni. I always heard for best results, you want the base of the antenna to be just over 36 feet above ground to avoid ground reflection, since a wavelength is basically 36 feet. Firstly, is an 11 meter wavelength truly 36 feet? If the above is true, if my current height is 34 feet, would it make a positive difference to raise it another 2 feet or more? I want it right. If it would make a positive difference I have no reservations about taking the time to raise it a bit more. Please advise. Thanks, |
Thehobo
Intermediate Member
Username: Thehobo
Post Number: 142
Registered: 2-2004
| | Posted on Wednesday, November 16, 2016 - 11:19 am: |
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if your satisfied with it the hight that its at, leave it as imo,2 more feet wont make that much differance.. now as the saying goes, hight is mite, meaning if you wood like better use of your antenna go for a big jump, like 10 feet or better.. my coily is at 32 feet and it does wonders for me.. if your sisuation is to were you have no trouble moveing the antenna up or down, woodent hurt to play with your hight..
thehobo
thehobo
269150 monitor ch.
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454
New member
Username: 454
Post Number: 2
Registered: 11-2016
| | Posted on Wednesday, November 16, 2016 - 8:57 pm: |
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Thanks for the reply. Now, what is a techs point of view on this? To be clear, my point is not whether or not I am happy with the height but rather if 36 feet is the height of a wavelength, then wouldn't it be to my advantage to get it up to 36 feet at the base? |
454
New member
Username: 454
Post Number: 3
Registered: 11-2016
| | Posted on Thursday, November 17, 2016 - 5:09 am: |
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Although I appreciate all the help I can get, I thought I would verify - I am in the "ask the tech"
Section of the forum am I not? |
Dale
Senior Member
Username: Dale
Post Number: 2299
Registered: 12-2002
| | Posted on Saturday, November 19, 2016 - 10:26 pm: |
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yes 36 feet is 1 wavelenth. however if ya near that height 34 feet raising 2 feet to 36 wont see much if any difference cause ya already so close to 1 wavelenth.. now if ya wanna raise it up for better performance raise it up too 54 feet to the bottom thats 1-1/2 wave lenth that will be worth ya effort
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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Charliebrown
Advanced Member
Username: Charliebrown
Post Number: 513
Registered: 10-2002
| | Posted on Tuesday, December 13, 2016 - 7:37 pm: |
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Actually I believe 72 would do better. Two wavelength. Not to disagree. Just I believe if your going to go to raise it might as well go for it. |
Tech833
Moderator
Username: Tech833
Post Number: 2370
Registered: 8-2002
| | Posted on Wednesday, December 14, 2016 - 12:50 am: |
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2 more feet AGL will make ZERO difference.
Since your Sirio antenna is fed at the base, there is some merit to the height above ground controversy in that antenna's case. However, the "magic number" (if you will) is 1/2 wavelength above ground, not a full wave or 2 full waves or whatever.
If the feedpoint of a 5/8 wave antenna is less than 1/2 wave above ground (or metal building or whatever), the takeoff angle will be very high. It works that way for both transmit and receive, but much more for transmit.
The thing is, the higher you get the antenna above EVERYTHING (not just ground), the better. Each foot below 1/2 wave is noticeable, but each foot above 1/2 wave is less and less noticeable as you go up.
Now, if you raise the feedpoint of the antenna from 20 feet AGL to 40 feet AGL, you will notice that for sure. In order to see the next real gain in performance, you need to double that, so 80 feet AGL. To get a noticeable improvement over that, you have to double THAT to 160 feet AGL, etc... Get the picture?
2 feet? - Absolutely no difference. 200 feet? - You betcha. But, at that point, we start talking about feedline losses, etc.
Your radio 'Mythbuster' since 1998
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Charliebrown
Advanced Member
Username: Charliebrown
Post Number: 514
Registered: 10-2002
| | Posted on Friday, December 16, 2016 - 8:27 pm: |
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Hello 833. Always great to learn something new. I thought it was the same as the I Max on angle. MERRY CHRISTMAS 833 AND TO ALL A VERY HAPPY NEW YEAR TO COME. MAY GOD BLESS EACH AND EVERYONE. |
Dale
Senior Member
Username: Dale
Post Number: 2305
Registered: 12-2002
| | Posted on Thursday, December 22, 2016 - 9:10 pm: |
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yes it is c.b. interesting read tech 833. so in the case of the 827 if one couldnt get it up high in the air they should get to at least 18 feet minumin at the very least?
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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Tech833
Moderator
Username: Tech833
Post Number: 2372
Registered: 8-2002
| | Posted on Friday, December 23, 2016 - 9:41 pm: |
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Dale- Yes. Minimum of (round numbers) 20 feet to the feedpoint.
There is only one base antenna for CB that works well below that, and they aren't made anymore. However, if you find an Avanti Astroplane, or one of its copies formerly called the "Top One" from Copper Electronics, then that will work clear down to almost ground level.
Charlie- Merry CHRISTmas!
Your radio 'Mythbuster' since 1998
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