scwis

We’ve explored this topic before, but we need to revisit it…

We’ve explored this topic before, but we need to revisit it…

I build part 15 AM antennas (as a hobby and a business) and I receive a ton of email questioning the need for a ground system.

Some of us can appreciate the need for highly technical information on these boards, but for the beginning part 15 broadcaster, some of these terms can appear to be frightening. So, here is the gist of the story regarding ground systems:

AM radio is basically a ground based radio service: people don’t realize it due to its great sky wave value. But in terms of very low power broadcasting, it is more important to concentrate on your ground wave than it is to imagine a huge, or even a mediocre sky wave. Your goal should be to serve your immediate area; we are talking in terms of 1 to 5 miles depending on your terrain and ground conductivity.

I’ve been quoted on this before, but I need to say it again; nearly 50% of your AM signal is due to your ground system; if you choose to merely pound in a ground/lightning rod, you are not building a ground system; you are merely grounding your system.

With some exceptions, nearly all LPAM kits or ready-built transmitters benefit from an AM antenna mounted in the ground.

As an example, the antenna I build is legal length; 108″ long or less after it is tuned. You can mount it on a mast pipe that is no longer than 18″ so in essence we are talking about a unit that is not much higher than 10 feet.

The ground radials are attached to the mast pipe; the transmitter ground is attached to the mast pipe so, we have a ground and we have an extension of the antenna.

What we have done is make the antenna “appear” to be 20 feet tall, instead of 10. Literally, the signal coming off the antenna will tend to dip to ground and not ‘float into the air’ as some people think it will. Those ground radials will serve to push that signal along until it runs its course.

I use 9 foot radials in the ground system I sell with this antenna simply because the antenna, basically, will average out to 9 foot tall. Remember that we want to concentrate as much energy as we can into the ground, not into the air! We are only using 1/10th of a watt!

I believe my message is getting through to the part 15am community; I’m getting a lot of letters about increasing the amount of radials and in so doing, the effect they will have on signal.

The answer is simple: as far as I know, no one has used more than 25 radials and has reported results.
I myself experienced an increase in signal of about 1/2 mile (which is a fantastic increase!) by doubling my radials.

There becomes a point where adding more and more radials will not be of service, just because we are using miniscule power. But to answer the big question, it is true that full power radio stations do use 360 degrees of radials; that is a lot of wire and a lot of work.

You need to look at where you live: if you live in a desert area, it may be best to increase your ground system….that is, to increase the amount of 9 foot radials you use. I’m not positive that increasing the length of them is important, although mine are generally 15 feet long. (I’m an experimenter and builder that is why they are long).

A desert environment would benefit from using 20 or even 30 radials, simply because you are sitting on dry sand. However, a Midwest environment could get by with a simple 10 radial installation. Overall, I do believe that the more radials the better, but I don’t see the need for 100’s of them in this particular installation.

I decided to write this because I got a letter from a customer who wants a 60 radial installation. As a businessman, that is fine with me, but for his location,(and his financial situation) I don’t feel a 60 radial installation is needed.

What I liked about his thinking was that he realizes how important the ground system is to his LPAM installation.

Sincerely,

Carl Van Orden
Antenna Guy
http://antenna18431.tripod.com/antenna.htm