| Author |
Message |
    
ryan
| | Posted on Saturday, December 07, 2002 - 11:16 pm: | 
|
http://www.widomaker.com/~xsamo/bulleti2.htm
i think this might be the one that i build for house use
|
DeadlEyes
| | Posted on Sunday, December 08, 2002 - 1:00 am: |
|
Good evening. I looked up the antenna you referenced. The transmission pattern is indeed a broadside pattern. If you feed the antenna at the top of the vertical elements the characteristic impedance should be 35 ohms. You should get a SWR of 1.6 or so (50 divided by 35).
Also you might want to put the antenna so that no one can reach the bottom of the vertical elements. Sometimes high voltage build up at the ends of certain antennas. The kind that make ya wish you never had touched it if ya get my drift.
I noted that he used cheap caulking tubes. You probably could use some scrap PVC pipe filled with sand or rocks to the same effect.
Let us know how it turned out.
DE |
Marconi
| | Posted on Sunday, December 08, 2002 - 4:16 pm: |
|
If you study more into this antenna, you will find that this antenna is reported to be very much affected by the height. The big advantage is supposed to be that the take off angle is very low, good for DX. At the right height, it is also supposed to eliminate all the typical higher angle lobes. If so, this should tend to reduce high angle local signals and interference.
Marconi |
Kb5lpa
| | Posted on Sunday, December 08, 2002 - 5:36 pm: |
|
The antenna theory of the bob tail curtain has been around for a long time. When one of the vertical radiators is eliminated (middle one), you have a half square, which is a dx grabbing antenna. You simply need to have it at least 1/2 wave length above ground for the design frequency. Check into Antennas and More for technical information on the half square.
I have one for use on 10 meters. It loads the entire band at less than 1.2:1 , even in the FM portion. The lobes are broadside to the top wire, nulls on the ends. Used it on a "dead" ten meter band one day and a VK came back to me[I'm in Texas]. Chatted for 30 minutes or so. California sounded as if it had been swallowed by the Pacific Ocean. One fellow (California station)tried to call me, had to go vertical to even hear him. Do not expect to work much of anything local with this antenna. A dipole/vertical would do much better. If you want dx, then a half square, or a bob tail will work.
73 de KB5LPA |
Marconi
| | Posted on Sunday, December 08, 2002 - 8:13 pm: |
|
KB5LPA, I have thought about using one of the 1/2 squares on 11 meters, but I think it is designed to be low to earth (18' or so for 11 meters). I understand that the higher angle lobes begin to pop up and reduce the DX effectivness and increase high angle signals if you start to get above a 1/2 wave length height very much.
I have a lot of trees in my area. I have a 4 element flat side yagi that is well below the tops of the trees and it works great even though. What was your experience with the 1/2 square on 10 meters regarding these factors. Do they work best if out in the clear open ground somewhere while remaining near the earth.
You also imply that the DX will be out of the US from a position in Texas. I am NW of Houston and I would like to know more about your experience with yours.
Marconi |
Kb5lpa
| | Posted on Monday, December 09, 2002 - 2:30 pm: |
|
While the half square is a dx antenna, I did not mean to imply that US contacts cannot be made on this antenna. I have made many. My signal is usually quite good with this antenna. If you can mount one at 1/2 wave above good ground, you can usually do quite well. Obstructions will have an effect on this antenna. Detuning objects(tin tool shed comes to mind,tv support pole) too close to it will have an effect on the pattern of it as well.
Out in the open is optimum for this wire. In both places I have run it, I have been lucky to have a fairly open area. My backyard has been ample to provide a good place to mount this antenna. I have not had it very high in either location. Never over 25 feet. Think of mounting it as you would a dipole, as high as you can get it usually makes it work well. Neat thing about a half square is that using those trees to your advantage as supports, you can probably get it pretty high and in the open(between 2 that are not too close). According to technical notes I have read, close to ground will not detune it as bad as a dipole. Higher is better with this antenna. At a 1/2 wave or better, you get the pronounced dx lobes it is raved about for.
From near Beaumont, I worked Africa with this. Lots of England stations, Poland, Yugoslavia, Czech Republic, Germany, Spain...you name it. However, when band conditions are not as good, US contacts were plentiful.[The condition of the solar cycle as you know affects dx.] It is a good antenna. I would not make it my only antenna, though. I have used it along with a G5RV and a vertical. Like all things with amateur radio, you never know what is going to work on what day.
For 11 meters, I would think it would do well on usb/lsb. I really would not even attempt to make a guess about am with things being the way they are. I have never tried it on 11, so I am strictly making a guess as to what may or may not work.
I hope you have found some of this of use. Good luck. Do go to Antennas and More and check out the technical notes on this antenna. Also use a search engine and you may be able to find more info.
73 de KB5LPA
|
ryan
| | Posted on Monday, December 09, 2002 - 7:10 pm: |
|
yeah, ill be only using it on 11 meters as i dont have a license to go anywhere else |
Kb5lpa
| | Posted on Tuesday, December 10, 2002 - 8:15 am: |
|
I re-read some notes on the half square and the lobes are aimed at transmission distances <1400 miles when mounted at 1/8 wave length(or higher) above ground if I am reading it correctly. In close work is definitely better suited for a dipole or the like. Mounted with the ends North/South, the lobes would favor US coverage and out. Lots of good contacts can be made with this antenna. As with all hf, when the band is open, it is open;when it is closed, no matter how many watts you run, you are warming the clouds and the worms!
73 de KB5LPA |
|
