Wave Length

[Drifter]

Can someone explain to me why it is said to put your base antenna up above one wave length 36 feet I think. I have my base antenna up 40' from ground to base of antenna plus i'm on a little hill. Should I raise my antenna higher or is 40' plus hill workable. I am also trying hard not to piss my neighbors off too much. They don't like the antenna.

 

[Master Chief]

Saying, "You should install your antenna at least one wave length above the ground." is a general statement used almost incorrectly for all antennas. This is NOT an exact description, but you will get a basic idea of what is going on.

GROUND PLANE:
The ground plane antenna works INDEPENDENTLY from the ground below it .... almost. When tuning one up, you want to be at least 10' above the ground to minimize reading errors due to reflections. Usually, any readings above a height of 10' to 18' are unaffected by the real ground below it because the antenna already has its own "ground" system made up of 3 or more radials. The antenna is stupid and doesn't know there is a real ground below it; it only sees the artificial "ground plane".

Mounting a GROUND PLANE antenna heigher than 10' to 18' will only increase its "view" or line-of-sight. Its like standing on top of a mountain; the higher you are, the more you will see. There are less obstructions like trees and buildings that could also interfere with the signals being transmitted out your antenna. CB frequencies are NOT "line-of-sight" like VHF and UHF frequencies, but getting them in the clear sure helps! Putting this antenna at 36' is only better than having it at 18' due to possible obstructions. 40' is better than 36' and 60' is better than 40'. The antenna does not know and does not care because it takes its "ground" with it! (Do not confuse RF ground with electrical ground for this discussion!)


BEAM ANTENNAS:
Beam antennas are a different monster all together! Their height above ground WILL change their take-off angle and pattern. A general rule of thumb is to have it one full wavelength from the ground. If you are a true DX'er (DX is OUT of the country, despite what most CB'ers think), you will have an adjustable tower that will allow you to change your take-off angle and hit other parts of the world (DX) or USA (DOMESTIC). Its like having a mirror on your ceiling (ionosphere) and a flashlight. Change the angle of the flashlight and the reflected beam will be is different spots. Changing the antenna's height above ground will change it's radiation angle.

Again, 36' (full wave) is a general rule of thumb but does not apply to every antenna.

BTW, the Antron-99 is not a ground plane antenna, just in case you were wondering.

 

[Drifter]

HaHa..... Thanks for taking the time to explain this.... This site rocks

 

[Drifter]

Another question>>>>>> I used guy wire to support my military spec. aluminum mast. I inslated the area were the guy wire attatch to the mast. I was worried about radiating RF down the guy wire. Do I have a legitamate concern??? and if it is. Will insulating the guy wire from the mast prevent RF from radiating down the guy wire??? I have a Ground Plane Antenna.

TIA

 

[Master Chief]

Yes, you have a legitimate concern. No, insulating them will NOT necessarily stop RF from radiating down the line.

Do you remember the fat lady who could break a wine glass with her voice? She sings, and the sound waves make the glass vibrate (resonate) until it destroys itself. The sound waves traveled through the air and made the glass vibrate.

The same thing happens with guy wires, especially if they are of a resonate length. Its like having reflectors and directors on a beam antenna! In this case, it would be a bad thing.

Commercial towers use insulators to break up the length of the guy wires in order to prevent them from adding to or taking away from the signal.

You want to use a non-resonate length of guy wire (7.281') I'm not going to go into how I came up with that number just yet, I'm still doing some tests.

Better yet, use dacron rope or Philystran and forget about having any problems of resonate guy wires!

 

[Switch Kit]

Very nice posts M-C .....I've always used heavy duty Nylon rope for my guy wires over the years on a Alpha-V-5/8 (my personal favorite antenna) , I would guess to say the only time they would have the chance to resonate would be if and when they got wet ?(I live in So Cal so that doesn't happen to much) But as far as TVI and all that goes /I always seemed to have less of a problem with the nylon rope and SWR ....I had a friend not to long ago change his nylon ropes because they got pretty old and beat up after about 5 years ......he went to steel guy wires ....totally screwed up his SWR on a 5/8 wave ground plane ...I told him he needed to isolate the wires from the antenna and or pole that he was using ....He went back to some freshly baught nylon again. (-:

 

[Drifter]

I was afraid of that..... I still get good reports thou.. I hope I am not tearing up the neighbor's TV and telephone.....they have not come a knocking yet...... I have to look into buying some Guy Rope.

Thanks

 

[erik_ark]

Another question:

Should the bottom or the top of the antenna be at at least one wavelenght above the ground?

 

[Master Chief]

Should the bottom or the top of the antenna be at at least one wavelenght above the ground?

The feedpoint, for the antennas that matter.

 

[erik_ark]

Should the bottom or the top of the antenna be at at least one wavelenght above the ground?

The feedpoint, for the antennas that matter.

OK thank you .

 

[RoadWarrior]

I have read that at 36 ft, 54 ft, ect. the takeoff angle
is the best. I don't know whether to believe this
or not. My antenna is 47 ft and does good.

 

[Master Chief]

I have read that at 36 ft, 54 ft, ect. the takeoff angle is the best.

That depends on where you want your signal to reach. Changing the height changes the angle and where you can reach. What works today may or may not work tomorrow. Mother Nature is not a fair person!

 

[RoadWarrior]

Yeah, your right Master Chief.
Too many things changing and varying...

 

[C2]

I did not understand why comms over two states away would not be DX? I thought DX was any skywave, or at least anything that was not groundwave.

I also thought that the TO angle would be affected by height for any antenna. I also believe that the TO angle for a GP verticle at the same height as a beam would be lower, which makes a verticle a good DXer as well.

 

[KingCobra_CDX882]

Hi all..

C2 ...

Yes
The TO for a GP vertical has a lower angle then does a beam..

therefore a Vertical can do Extremly well for DX
I have spoken all over the world using Jay's I-10K

However
Do not Ignore the posible advantages of a Beam..
for they effectivly Magnify (in laymans terms) the out put power
without adding more power from say a amp or linear..
this is why it is usally far more effective to have the best antenna posible.....
for a 3 a 6 or even 12 or perhaps 18 db gain is obtainable with a very good antenna..
this is done far cheeper then would be a equivalant db gain gotten from a linear-amp..

however
many people do not have the room or ability to put up such antennas

then again
some do both exellent high gain beams plus exellent linears

let us not forget that a beam intensifies it's pattern in a narrow
beam...
so you get to listen greatly in that direction while rejecting unwanted noise from other directions..

yet the Vertical GP gets basiclly a 360 degree talking and listening..

Lastly..
Mother Nature has the last world