Define Ground Lead

Tim-in-Bovey I think asking about RF ground is always a good topic because the ground system is key to getting the best results from a transmitter system.

This topic will always come up and it should always be discussed and reviewed because it is complex with many different opinions and a lack of clarity in the rules.

I will wait at the end of the line and enjoy the comments as they come in, and probably later I'll get to yacking about grounding of antenna systems.

I agree that it's up to the interpretation of the inspector.

However, the 'spirit' of the 3 meter rule is that the radiating elements of the antenna (which includes the ground lead) can't be over that 3 meter length.

Horizontal ground radials perpendicular to your antenna don't radiate, whether they're installed at ground level or even elevated.  If they're angled, then they do.

If you have an elevated install, and a short ground wire attached to something metal such as a mast, then that mast can also radiate.  Historically that type of installation has been allowed, but recently not so much (showing that it is indeed the interpretation of the inspector that carries the final vote on ANY installation).

Agreed, if the guy's having a rough day, it could be rough for an operator...not that they do that purposely, but human nature being what it is, interpretation can get twisted one way or the other. My own take is that elevated radials connected to the TX ground lead could easily be interpreted as part of the antenna system, and top hat elements the same.

But, having said that, I wouldn't let it stop you from experimenting. I've done it too, but it doesn't seem to have increased signal strength all that much. Not sure why...maybe the noisiness in town has more to do with excessive data transmission on the power lines, or that the antenna was at the same 'level' as the power lines, or that a field of trees is not helping, or some combination.

Remember, AM radio is ground wave-based. For licensed stations with lotsa power, it's daytime ground wave and skip (long distances) at night. But for this flea-powered stuff, daytime is the only real consideration. We must just put up with the longer range of interference at night, or convince listeners to get better receivers, or provide a cheap means to offer external loop antennas they can use to focus in on the signal.

Probably the best deal out there in new receivers is the C Crane High Performance AM/FM radio. It's available from C Crane of course, but is also offered by Radio Shack. They've sold quite a few here, because reception is notoriously poor out here in the San Juan  Islands. Virtuallty all those people said it's the best radio they ever owned. The AM section boasts a dual large ferrite core coil antenna system. When my system was on my (former) boat, that radio could get a great signal inside the store, florescent lights, wire reels, power transformers, TV's, and all the other usual rat shack stuff.

Anyway, AM radio being ground wave, it may be better for the radials to actually be buried an inch or so in actual earth. This is the way monopole AM radio stations have been doing it since the 1920's. The only real improvement is the kinstar low profile cage system  http://www.kintronic.com/, and that only because land space needed for a monopole with 150' antenna and 120 1/4 wave ground radials is hardly available anymore in the U.S. But, that's for licensed stations. I'm not sure how it would work in miniature for a Part 15 station, but I have most of the materials to build a conical cage antenna on the ground.

When I get it built and up and running, I'll post pictures. Sure hope it works well 😉

Elevated radials perpendicular to your antenna will not radiate - they perform the same function as at ground level, and it is one way to legally get your antenna elevated, with a ground.  If you can't install on a flat roof, then you could use copper pipe for radials.  Of course, you still have the lightning protection issue.

If those same radials are at an angle, say, on a sloping roof, then they WILL radiate, and would likely be considered part of the antenna.

But there's no telling how an FCC inspector might interpet elevated (perpendicular) radials.  You're always safer (legally wise) to install your antenna at ground level.

AFTER following many discussions on "ground" and "ground-lead" I have developed a set of beliefs of my own, but have been avoiding writing about it because it's difficult to use clear language when describing geometric patterns affecting electrical behavior.

GROUND LEAD -  is a single wire from the transmitter's negative side to either an earth-ground or a "qualified" ground. I'll try to explain.

EARTH GROUND - is a wire either laying horizontal at the surface of the earth or buried a given distance below the surface of the earth. It is generally claimed that ground wires parallel to the earth do not radiate while they are at or below the earth surface. Maybe that's true, but I believe even if at the earth surface, a "qualified" ground is most effective.

QUALIFIED GROUND - is a ground located either below or above the surface of the earth but which meets the qualification of being self-canceling. Artisan almost described it; it is a horizontal shorted-dipole center-fed by the transmitter's ground lead; a minimum set of two radials. This serves to lower the overall impedance of the total system so as to reach fuller resonance. Additional radials can be added in sets of two, no odd numbers, all of equal length so they exactly reach null and do not add radiation.

A SINGLE HORIZONTAL WIRE ABOVE THE GROUND FED AT ONE END BY A GROUND LEAD WILL RADIATE.

That is the best basic definition I can manage to write at this time. Please improve or correct anything I've said.

Here is a very good, easy to read document on vertical antennas and radial grounds:

There is a lot of good information in that paper, but there are a few points there that are not well-supported by science and experience.  For example:

It should be noted that a ground rod is useful only as a d.c. ground or as a tie point for radials. It does little or nothing to reduce ground losses at r.f. regardless of how far it goes into the ground.

A NEC4.2 analysis posted in other threads here shows that a 3-meter vertical ground rod buried directly below a 3-meter monopole has an r-f resistance varying from 268 ohms to 25 ohms for earth conductivites of 1 to 15 mS/m, respectively.  Those resistances produce a 5:1 change in radiated power over that resistance range, which really is not "little or nothing."

The text below was taken from a post I made on another website:

Here are the results for the ground path loss of a NEC4.2 model of a monopole on 1640 kHz with various lengths of ground rods (5 mS/m d.c. 13 earth conductivity):

Length, meters    Resistance, ohms

        1                       177.2

        2                       101.2

        3                         72.5

        4                         58.2

It is clear that the length of the ground rod does have a significant affect on its r-f resistance.

Elevated radials:  The problem of ground loss resistance may be avoided to some extent by mounting a vertical antenna some distance above the earth over an artificial ground plane consisting of resonant (usually 1/4 wavelength) radial wires. Four resonant radials are considered to provide a very low-loss ground plane system for vertical antennas at base heights of 1/2 wavelength or more.

The monopoles of several licensed AM broadcast stations are installed with their bases about 10 feet above the surface of the earth, and are driven against four to six, horizontal radials elevated the same height as the base of the monopole.  They perform as well as if the r-f ground consisted of 120 horizontal, buried radials each 1/4-wave long.

Ten feet is about 6.2 degrees at 1700 kHz and even fewer degrees at lower frequencies.  So it is not necessary to elevate the base of a vertical monopole to 1/2 wavelength (= 180 degrees) or more above the earth in order provide "a very low-loss ground plane system for vertical antennas."  This result also is shown in NEC analyses of such systems.

In my post above giving my beliefs on antenna ground systems for AM radio broadcasting I used the expression "QUALIFIED GROUND" to describe two apects... 1.) EITHER a radial ground system located above the earth, i.e., an elevated ground; 2.) OR a radial ground system located below the earth, with the QUALIFICATION being self-nulling so as to avoid radiation from the ground system.

In his post, PhilB used the word ARTIFICIAL to describe an elevated ground system to differentiate it from a ground system actually on or below the earth.

I wonder also whether the word VIRTUAL might be applied to any ground system not on or below the earth (elevated).

In my post I declared that radials need to be present in even pairs, no odd numbers, and although neither PhilB nor Rich(F) specifically said the same thing, the number of radials given in their examples were in all cases EVEN numbers, thus implying an agreement with keeping radials in even (not odd) numbers.

As it turns out the term "Virtual Ground" is already taken and we can't use it to describe elevated grounds...

http://en.wikipedia.org/wiki/Virtual_ground

And many other terms have come to attention by studying the section on "Safety Ground", including "technical earth", "special earth", and "audio earth."

http://en.wikipedia.org/wiki/Safety_ground

Virtual defined: "In effect though not in fact."

For closed loop op-amp inputs a virtual ground acts as a very high impedance dead short.

This has proven to be very interesting and educational. 

Exactly what, legally does the FCC consider a "ground lead".  The length of a wire from the lug on the transmitter to the clamp on the ground rod?  What if the ground rod sticks out of the ground 6 inches? Does that add 6 inches to the ground lead?

Really, all for the sake of discussion I guess, as we've already determined it is based on the interpretation of any given inspector.

Tim in Bovey

Are they the same thing? Can you speculate without conjecturring?

Member kc8gpd once submitted a request to the FCC under the FIA (Freedom of Information Act) for the publication used by the FCC for Part 15 Inspections and was sent a sloppy document loaded with redactions that concealed anything of value from the reader.  Am I correct on this?

It was member Bruce MICRO1700 DOGRADIOSTUDIO2 who shared a comment made to him by an FCC inspector, "If it's within 10-feet by 10-feet we have no problem."

Ten-feet-by-10-feet is a significant measure, because you'd have the sum total of 10-feet vertical and 10-feet horizontal which would boost things a tad.

What if you build a hill?

What is the definition of a hill?

Could it be 20-feet of mud in a stack of large drums to give legal ground up high?

Rich,

I think the way you word the analysis of the RF ground resistance of a single ground rod can mislead part 15 enthusiasts into thinking that a ground rod is all you need to get good performance from their transmitter/antenna.

Copper clad steel ground rods are most commonly available in a length of 8 ft. That's about 2.44 meters which falls in your tabulation at about 85 ohms with "average" ground conductivity of 5mS/m, DC=13. That 85 ohms is way too high for good performance. Even the 58.2 ohms you show for a 4 meter rod is still way too high for good performance, not even considering that you can't get a 13 ft. rod unless you get it custom made and find a way to drive it into the ground.

An inexpensive 500 ft. spool of light gauge wire will be enough for 16 radials, each 30 ft. long. Such a radial system can be easily implemented with the lawn/garden/landscape staples method without digging. By comparison, the ground resistance will be less than 10 ohms (likely less than 5 ohms) and it will be a stellar performer.

Of course, the performance of a single ground rod compared to a radial system will converge as the ground conductivity increases toward maximum, but very few people live in the maximum conductivity world, so there will always be a big advantage to a good radial system. In fact, for obvious reasons, most people live in the "average" conductivity areas.

"What if you build a hill"?

If you put the antenna on a natural hill, that's OK.

If you build a hill that looks like a natural hill, that's OK.

If you build a hill that looks phoney, that's not OK.

If you don't agree wtih the FCC agent's judgement, you can hire a lawyer and challenge it. You need a lot of money for that.  You might win the case, or maybe you might lose.