Mr.Marshall Johnson,
Thank you for your response/attention .fortunately here in Indonesia ,we may build licensed Medium wave broadcast radio with power from 500 watt to 1600 watt (transmitter I have build) ,and we used it as Gospel Radios.
The problem we have, is building an Efficient antenna,WE don't have enough land and fund to build a full quarter wave antenna ,and especially laying the quarter Rf ground radial.
So after looking in the Internet trying to find a solution, I have read about EH antenna,Gap Antenna,CFA antenna, Isotron antenna, A small medium wave antenna ,and according the designer it's a good Antenna.
After searching the Internet what a coincidence,I've found Your web discussing/using the Isotron Antenna.
May be you can help me,and give me advise building a small compact Medium Wave antenna that's an efficient Antenna.
Thanks
Gito.N
I don't know if MW antennas are required to have some minimum efficiency in Indonesia, like in the U.S. If no minimum efficiency is required, just erect a base-loaded monopole as high as you can make it, and construct as good a ground screen as you can. This kind of antenna will work as well, or better, than the Isotron, EH, and the CFA. These three antennas are based on theories that don't make any scientific or technical sense.
The theory of the Gap antenna is not pure bunk, like the other three, but I suggest that you don't bother with the Gap either. The Gap antenna uses an elevated feed point, and that, within limits, is not a bad idea. Short, grounded, center-fed, vertical dipoles have been used for low-power licensed medium-wave broadcasting for years, and they work particularly well when the real estate for the ground screen is limited. Because of the center feed, some of the displacement current of the antenna flows from the top dipole arm to the bottom dipole arm, rather than all of it flowing through the ground, as in bottom feeding. This reduces the size of the ground screen that is needed.
Whatever antenna configuration you use, be sure to get the services of a reputable antenna consultant. Feeding an electrically-short antenna with a kilowatt, or so, is dangerous, because very high voltages are generated due to the high antenna reactance. You also need someone who can figure out how to design the tuning network for feeding the antenna with your transmitter.
Thank you Ermi Roos ,for your Reply.
Here in Indonesia we have no restriction to build an Antenna,the only restriction ,you must build a vertical antenna,I' have build 135 feet(45 meter) antenna ,using 60 feet(20 meter) of the guy wire as top load,using tuning coil at bottom,But we can lay the RF ground radials,because we have not enough land and funds,So I thing there must be looses in the ground.
Thingking of that ,I like to find Antennas without ground radials but Efficient .
Ermi can you give details/design of the vertical dipole you wrote about
It ,it will be a big help to me.
Thanks
Gito.N
The vertical antenna you described is pretty good, and will give a lot better results than the CFA, EH, and the Isotron. You will need a connection to ground. Don't listen to anybody who tells you you don't need a ground connection. However, since there is no minimum antenna efficiency requirement in Indonesia, just a ground rod driven vertically into the earth will give you a working antenna system. In that case, your "radials" are just the dirt under the antenna. It's not very efficient, but it will work. You will have at least a few hundred watts of radiated power, and this will provide appreciable range.
The trick of the bogus antenna design promoters (CFA, EH, Isotron) is that even an inefficient antenna system can be heard a long distance away, and you can be easily fooled into thinking that the antenna is working well, altough it is very inefficient.
Since you don't need radials to get the antenna to work (although inefficiently), anything you do to improve your ground will be a bonus. Run a wire from the antenna ground rod to a (metal) cold water pipe. A single quarter-wavelength wire from the ground rod, just under the surface of the earth, bent to fit your space, will help. Don't bother with radials. Burying some chicken wire fencing just below the earth, and connecting it to the ground rod, will improve the ground substantially. Just get whatever buried netal you can install to work for you. Use the space you have!
We Part 15 hobbyists would love to be allowed to install this kind of antenna.
Thank You Ermy Roos.,for giving me answers/input to my questions.
thanks
Gito.N