3 Meter Regulation Question

Unfortunately the 3-meter limit includes antenna, transmission line and ground lead, impose a strict limitation.

But anything physically buried BELOW the surface of the ground is fair game, and makes a major improvement on radiation distance.

At a minimum an 8-foot ground rod pounded into the earth and attached to the transmitter ground lead will provide both improved signal field and lightning safety.

But if you fan 64- radials out at surface level each about 30-feet or more, you will achieve the distance of which part 15 AM is capable.

The ground wires or rods located below ground are not able to radiate, but do provide the vital process of a "return" path for completing the RF output circuit. I'll let someone else explain that.

As I interpret that is says to me that if I add the length of my antenna, the feedline, and the ground system... In total they cannot exceed 3 meters.. Is this the correct interpretation?

As a matter of physics, the "ground system" does not include the conductors that are buried in the earth. Those buried conductors do not produce useful, far-field radiation.

However the conductors connecting the r-f ground terminal of the transmitter to such buried conductors ARE a radiating part of the antenna system.

Thanks for the information guys.....

Wow, so its about as restricted as I thought...... I would have to put this at ground level outside in order to do a radial system like that.

What do you guys think is better...?
High in the air with poor/no ground or...
On the ground level with a nice sub-ground radial system?

What do you guys think is better...? High in the air with poor/no ground or... On the ground level with a nice sub-ground radial system?

Below is a link to a NEC analysis relating to your question.

The decision as to which system to use is that of the reader.

Corrosion, I'd recommend that you do a search of the Part 15 web site for more information, if you need it. There have been many threads (and even more posts) regarding the 3 meter rule, grounds (and the apparent contradiction of the Talking House/ATU combination).

Thanks everyone...
Yeah I've heard a lot of back and forth on these ATU's and TH units.

I would just put up a good feedline and make the antenna 3 meters and just not worry about it being slightly out of spec... but since I'm a licensed ham... if I ever was audited or a complaint ever filed there certainly wouldn't be any leniency because well.... I know the law as far as their concerned... I certainly know Part 97 anyway.

<cite>As a matter of physics, the "ground system" does not include the conductors that are buried in the earth.  Those buried conductors do not produce useful, far-field radiation.<cite>

Confusion here Rich.  Maybe I misunderstood. When a local AM here had a crappy "ground system" the far-field range was poor. When the ground system was replaced the range improved dramatically.  Typical ~90 degree system.

RE:  Confusion here Rich. (etc)

Buried radials used with a monopole permit the efficient return of r-f currents induced in/just below the surface of the earth within a 1/2 wavelength radius from the monopole.  Those currents are the source of all of the r-f current that can flow along the radiating conductors of the antenna system.  Without the buried wires, the currents in the earth are reduced by the resistance of the earth to the flow of that r-f current back to the "ground" terminal of the transmitter/antenna system.  The earth is not a very good conductor of r-f energy.

In a monopole antenna system only conductors that are not buried in the earth produce useful far-field radiation.  However the amount of far-field radiation they can produce depends on the r-f current flowing along them.  A low-loss set of buried radials maximizes the current in the unburied conductors, which increases the radiation efficiency of the antenna system.

So, while the buried radials (ground rod, cold water pipe etc) do not produce useful radiation directly, they enable more of it to be produced by the unburied conductors.

The posting by rich explaining how non-radiating ground radials contribute to more efficient radiation from the antenna is the best description of this illusive concept ever written here at part15.us.

If it has ever been expressed as well or better, you may correct me by linking the other references.

For us radio amateurs (not HAMs) it can be difficult to compose a mental picture of how radials are of benefit if they do not radiate. By reading and re-reading rich's post this idea may begin to paint a brain picture.

As an audio specialist, I have always (incompletely) viewed the RF antenna as needing to couple with the air. There are reasons why this is not what takes place. Radio waves don't need air for propogation, which is why radio communications are possible in outer space.

Think of the transmitter's RF output as needing TWO poles to succesfully link with the transmission path: the antenna is the "positive pole" connected into open space. The earth/ground is the "negative pole" where the transmitter depends on the signal injected into space to return into the RF circuitry to form a "complete circuit".

The earth, as rich notes, is an inefficient conductor, a limitation that is greatly overcome by enlarging the size of the radials that achieve an RF electrical bond with the earth.

I have explained it again using other words with the hope of double-emphasizing the key message.

Thanks for your input Carl,

As per the "Not HAMs" comment, I just wanted to throw out there that nearly always use the term "Amateur Radio" however I was not aware how well part 97 and the like was understood here when I made that post... So, to avoid confusion I use the word ham because most people get a general idea of what I'm talking about.

That being said if my license plate said "Ham Radio" on it I probably wouldn't have an Amateur plate at all.