Antenna Placement

As long as the feedline+antenna+ground wire does not exceed 3 meters (that's the actual 3 meter rule you refer to), then an elevated mount would be legal under Part 15 rules. Although you should note that if you ground your transmitter to that pole (assuming it is metal), the FCC these days considers the length of the pole to be part of the ground wire, and you would therefore be violating the rules.

The subject of the 'ground' within Part 15 rules tends to be a hot topic, and you probably should search this site for the many threads and posts that pertain to it.

I guess what I am unclear about is this - if you elevated your transmitter/antenna let's say 20 feet - you somehow have to get a ground wire from the transmitter to ground. How do you get the ground wire to ground legally without violating the 3 meter rule?

There is no way to legally ground your antenna per the part 15 rules and regulations if your transmitter is at a height of 20'.

You could attempt to run a ground line along your power and ground it to an outlet.. but short of that its a no-go.

Also if you mount to a pole you MUST make sure that your antenna is not conducting to your 20' pole, because if it is your antenna is technically much longer... about 30' and it would be a violation of the part 15 rules and regulations.

How do you get the ground wire to ground legally without violating the 3 meter rule?

Some have suggested using a filter or choke to prevent r-f current from flowing on a "lengthy" conductor to the earth.

Below is a post I made on this subject from a Pt15us thread last November:

However a tuned (narrowband) r-f network optimized for the center frequency of an elevated Part 15 AM transmitter+whip can prevent most radiation by that transmit system from a long "ground" conductor -- and without much affecting whatever lightning protection is provided by that long conductor and whatever it connects to at its base [ground rod(s), etc].

However the radiated fields produced by an elevated system using such a network probably will not be as high as if the system was installed with the base of the transmitter a few inches above the earth WITHOUT that network, when using a very short conductor connected to the same ground rod(s).

The reason for the reduced fields from the elevated system with the decoupled ground lead is due to the much higher impedance in the return path for radiated r-f earth current back to the "ground" terminal of the transmit system.

An analogy for d-c circuits is the brightness of a "stock" flashlight to that when a large-value resistor is added in series with the flashlight bulb.

I have seen a few LPAM guys that have elevated their antennas upward as much as 50 feet to increase range. I guess I need to contact them to see how they legally grounded it. I can't imagine they could run it without a ground and get any real range and I can't imagine using the ground back to the power outlet would be efficient either.

I am trying to get my set up legal and I appreciate all the feedback.

Through many discussions here it is seen that there are AM systems which are elevated and pass FCC "inspection" and there are some which are cited for violating the 3 meter rule.

The safest approach, I believe, is to mount the transmitter at the base of the antenna system at ground level using buried radials as the RF ground. The "ground lead length" is then the length of the wire connecting the transmitter to the radials which is very short allowing most of the 3 meter length budget to be spent on the antenna.

Here's a photo of such an installation which gives about a one mile range on a car radio.

And another view close up at the base. The transmitter is in the gray box.

Neil

Elevation doesn't help much. The key is to make a good "Launch Pad" under the antenna. Keep the xmtr close to the Lanch pad (Buried ground wires) with a legal length antenna and you will get good results and no hassles or questions about ground lenght..

It takes a 20' circle to make a good ground area under a xmtr..