| Author |
Message |
    
Mikefromms
Intermediate Member
Username: Mikefromms
Post Number: 161
Registered: 6-2003
| | Posted on Saturday, May 08, 2004 - 7:56 pm: | 
|
This may seem like a dumb question, but I'm wondering if a G/P can be put up too high in the air? Is there a sweet spot where it might work it's best then start giving dimishing returns as you pass through that sweet spot and go higher? Some guys around here who have had high antennas have stated that it was a waste of tower or effort to go higher than 150 feet. Could wavelength affect this greatly? I know the Astroplane works best compared to other antennas close to the ground and starts losing the race with other when it goes up higher. What are your thoughts on this? Maybe this will spark a good conversation.
mikefromms |
Allagator
Intermediate Member
Username: Allagator
Post Number: 274
Registered: 9-2002
| | Posted on Saturday, May 08, 2004 - 9:44 pm: |
|
hey MIKE if you cant see it anymore would be a good time to stop !!!!!! CHECK YOUR LOCAL LAWS FOR THE HEIGHT LIMITS !!!!! |
Allagator
Intermediate Member
Username: Allagator
Post Number: 275
Registered: 9-2002
| | Posted on Saturday, May 08, 2004 - 9:48 pm: |
|
hey MIKE if you cant see it anymore would be a good time to stop !!!!!! CHECK YOUR LOCAL LAWS FOR THE HEIGHT LIMITS !!!!!but there is what they call sweet spots but at 56 foot with a M104C nothing but the old PEN 500 works great at 15 foot !!!!and this is im my country it mite work great in your part of town !!!
Allagator |
Ca346
Advanced Member
Username: Ca346
Post Number: 753
Registered: 8-2003
| | Posted on Saturday, May 08, 2004 - 10:01 pm: |
|
Don't forget to calculate in the cost of all those red blinking airplane lights...  |
Taz
Senior Member
Username: Taz
Post Number: 2676
Registered: 11-2001
| | Posted on Saturday, May 08, 2004 - 10:21 pm: |
|
Well, the wavelength thing isnt a bad thing to go by.
11 meters has a wavelength of 36ft.
So, mounting your antenna at 36 feet its at 1 wavelength, 72 is 2 ect ect ect... |
Jon666
Intermediate Member
Username: Jon666
Post Number: 186
Registered: 11-2003
| | Posted on Saturday, May 08, 2004 - 10:23 pm: |
|
rule of thumb ia about 36feet
any higher put a blinking light on top hehe |
ELCO Guy. (Unregistered Guest)
Unregistered guest
| | Posted on Saturday, May 08, 2004 - 11:18 pm: |
|
Not a dumb question at all. In fact it is quite a good question.
IF you read all the antenna books, they state more often than not that the best situation is at least one wave length above the ground or higher. This is to reduce the effect of ground proximity effecting the radiation pattern of the antenna to its minimal amount.
HOWEVER as most owners of big gun stations will tell you, the taller the better. The problem with that is, other than ligtning of course, is that you will need a much longer run of coax which increases in line loss as the coax gets longer. Unfortunately, line loss also effects received signal as well as transmit signal. So use the coax with the lowest possible loss.
As to the local restrictions mentioned above this is a very valid legal point. Some planned communities either restrict outright or limit any type of external receiving antenna height. Strange, what we find a beauty of a site they find as obnoxious.
Signed
That darned ol ELCO Guy |
Dan in WA (Unregistered Guest)
Unregistered guest
| | Posted on Saturday, May 08, 2004 - 11:38 pm: |
|
FCC says 60 feet above ground level or building structure for the radiating element of an omni-directional antenna (your choice for compliance). A whole lot more rules apply if you are near an airport. Antenna design determines optimum height based on radiation angle for maximum range, regardless of regulations. IE, it depends on which antenna you own and local conditions. |
Tech833
Moderator
Username: Tech833
Post Number: 680
Registered: 8-2002
| | Posted on Saturday, May 08, 2004 - 11:57 pm: |
|
The FCC rules state that the top of an omnidirectional (ground plane) CB antenna can be either no more than 20 feet above a structure it is mounted upon (like a tall building) or no more than 60 feet above ground level.
If this is for ham radio, then the limit is 200 feet AGL. Now, about the wavelength issue...
There are 'sweet spots' in mounting height for lower takeoff angles. That would be with the feedpoint at 1/2 wave multiples above ground. For instance, at 10 meters the heights would be 17 feet, 34 feet, 51 feet, 68 feet, etc. It does NOT need to be exact.
No matter what, the higher the better. |
Pig040
Intermediate Member
Username: Pig040
Post Number: 404
Registered: 7-2003
| | Posted on Sunday, May 09, 2004 - 9:30 am: |
|
Mikefromms, not a stupid question at all, I have often wondered about that myself. So our answer is, the higher the better, but do it at half wave multiples, c'mon all you techs, do you agree?? |
Tech833
Moderator
Username: Tech833
Post Number: 681
Registered: 8-2002
| | Posted on Sunday, May 09, 2004 - 11:36 am: |
|
Yes, I agree with myself. |
Mikefromms
Intermediate Member
Username: Mikefromms
Post Number: 163
Registered: 6-2003
| | Posted on Monday, May 10, 2004 - 5:30 pm: |
|
Thanks for the good discussion. Now, what if you had an Imax 2000 and it radiate from top to bottom (I think I'm right or am I), and instead of mounting the bottom 72' you mounted it at say 85', as long as some part of the antenna was touching or within the 1/2 wave multiple would this work as well as straight out 72'?
mikefromms |
Tech548
Moderator
Username: Tech548
Post Number: 31
Registered: 5-2004
| | Posted on Tuesday, May 11, 2004 - 2:21 am: |
|
Tech833
You ALWAYS agree with yourself. I've often wondered if you and yourself ever argue with each other.
Jeff. |
Mikefromms
Intermediate Member
Username: Mikefromms
Post Number: 164
Registered: 6-2003
| | Posted on Tuesday, May 11, 2004 - 10:16 am: |
|
I've been doing some reading on "the ulitmate cb" website. Pretty good stuff. Low takeoff angle is the goal is the goal to the antenna height/position we choose.
Speaking of low takeoff angle, in case anyone missed it in one of my other comments elsewhere, the astroplane works fantastic close to the earth. I found that mounting it about 9 or 10' from the bottom ring to solid earth all around (not on the side of a house) that this antenna hears locals better, yes better, than my thunder 8 hears locals 70 feet in the air! I got the same reports on my transmit. I couldn't believe it myself. Why? I take into consideration loss of signal in long run of coax (170ft of 213) and lower takeoff angle for signal. Now long distance is another story. Strange, huh. Now, that astroplane might not improve that much as I go up in the air but that rascal really must be the best groundplane low to the ground. And that's just what the tech told us in his antenna tests of several groundplanes right here on this site. Read and learn. I'm still learning.
mikefromms |
Tech833
Moderator
Username: Tech833
Post Number: 683
Registered: 8-2002
| | Posted on Tuesday, May 11, 2004 - 8:08 pm: |
|
Jeff,
When I begin to disagree with myself, I know it is time for bed.
Mike,
Yes, the Astroplane (or Copper's Top One) is excellent when it is mounted low. It makes very little difference when you mount it higher. It is one of my personal favorites.
A long time ago, some Cbers must have figured out the whole takeoff angle thing, because I can remember ground plane antennas mounted upside down from towers and trees. I never stopped to ask any of them why (I am not comfortable with strangers). Maybe they 'got it' for a while. |
Mdiver
Member
Username: Mdiver
Post Number: 90
Registered: 11-2003
| | Posted on Tuesday, May 11, 2004 - 10:24 pm: |
|
Thanks Tech833 and Mikefromms |
Bullet
Intermediate Member
Username: Bullet
Post Number: 334
Registered: 7-2003
| | Posted on Wednesday, May 12, 2004 - 4:32 am: |
|
500ft max. you wont get anymore angle lowering effect after that.
(so ive read, you wont ever see this ole boy that high)
i do know a fella that said his six element quad
did a better job at 72 feet than it does at 108 feet now.
ive never bought into the whole wavelength wives tale thing when it comes to antennas.
i go up 10 ft at a time untill i run out of tower,nerve, or untill i get the best signal. |
Tech548
Moderator
Username: Tech548
Post Number: 40
Registered: 5-2004
| | Posted on Wednesday, May 12, 2004 - 2:26 pm: |
|
LOL. Good post Bullet.
The reason why his beam does a better job at 72 feet is because it sees a much further horizon. Or simply put, the higher the antenna, the greater the distance it will be heard.
I too, Bullet, do not climb beyond around 60 feet anymore. When I was much younger, I looked forward to climbing as high as possible. I was fearless back then. Now I'm just plain scared.
In the dictionary there is a word that describes this syndrome. I'm not really sure how it's pronounced but it's spelled, A-G-E.
Jeff. |
Tech833
Moderator
Username: Tech833
Post Number: 686
Registered: 8-2002
| | Posted on Wednesday, May 12, 2004 - 2:48 pm: |
|
Bullet.
Check out the patterns shown on the Decibel website. Height above ground in multiples of 1/2 wavelength does make a difference on lowband. That is a proven fact that is well documented, even in the ARRL Antenna book. |
Rich_1833
New member
Username: Rich_1833
Post Number: 3
Registered: 5-2004
| | Posted on Tuesday, May 18, 2004 - 11:55 am: |
|
so say you have a imax 2000 and you want to stay under around 35 foot ( the base of the ant. ) how high or were should you go with it or put it. |
Mikefromms
Intermediate Member
Username: Mikefromms
Post Number: 169
Registered: 6-2003
| | Posted on Tuesday, May 18, 2004 - 1:24 pm: |
|
Thirty-four feet and 11 inches at the base.
The higher the better with that one for sure and add the groundplane kit.
Welcome aboard, Rich 1833.
mikefromms |
Tech808
Moderator
Username: Tech808
Post Number: 2411
Registered: 8-2002
| | Posted on Tuesday, May 18, 2004 - 5:57 pm: |
|
Rich 1833,
Place the Bottom as Close to the 35' as possible or as high as you can to the Base of the IMAX and you should be able to place it about anywhere you want.
Also Tech833 recommend's that if you cannot get the bottom of it to a full wavelength 36' to use the GP Kit with it.
Tech833 Wrote GREAT Reviews on Both the Imax 2000 Exposed and the Imax 2000 Ground Plane Kit Reviewed. 
Both Reviews are in the Subscriber Preview area under Product Reviews.
Hope this help's.
Lon
Tech808 |
