I have an SSTRAN with the base loaded coil antenna. I was wondering if there is a way to build a directional antenna for the SSTRAN. If so would it make any difference in range. I am assuming the copper pipe used for the SSTRAN coil antenna is acting as an omni antenna. I want to shoot the signal in a specific direction and was thinking that a directional would be better and give me further range. Any thoughts?
Your base loaded antenna is essentially omni directional. If you want to shoot more signal in a particular direction, use as many radial wires at least 1/4 wavelength long from the base of the antenna toward that direction (fan them out in an arc, of course). I would recommend a 3 meter circular ground screen at the base, in addition.
About the only way you could make a directional array would be to use a passive reflector element. I don't imagine that the efficiency would be very high, but you could look into it further. Maybe someone has tried it. I think it is impractical to directly drive two elements, due to the restrictions in the FCC rules on a "single 3M element".
If there is a particular area that you want to cover, you might consider just adding a second transmitter at that location. Others have used that technique successfully.
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Directional antennas consist of what are called directors and reflectors. These "beam antennas" consist of elements spaced an appropriate distance from the driven element and are practical above about 7 MHz in services where there is no antenna length restriction (such as the ham bands). In the AM broadcast band, multiple driven elements can be used but the bad news is the spacing required is several fractions of a wavelength and the phasing needs to be carefully controlled. For vertical radiators this is hundreds of feet of separation and is not practical for part 15 use.
You might consider a loop antenna or a rhombic but the size will be huge due to the long wavelengths and there will be questions about the 3 meter rule.
You ask a good question for which there is no good answer given the nature of part 15 AM.
Neil
When using a radial system, is it critical that I use bare copper wires? I have a roll of shielded #12, will that work ok for the radials?
You can use your shielded #12 wire and that will work fine. I have been using a radial ground plane under my 40 meter vertical for many years that was constructed of #12 house wire, and it has held up very well. Finer wires will also work quite well, but if you have the #12 available, it will probably hold up better.
Good luck!
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