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Ground Rod VS Radials

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Ground Rod VS Radials

Following real-world experience I am taking the position that only ground radials are capable of pushing a part 15 AM station's range to its maximum legal outreach.

So many of us have tended to believe that a ground rod can accomplish something of the same thing but I find otherwise.

Think of it as a 3-choice process...

A part 15 transmitter with only a 3-meter vertical antenna and no serious ground will not provide impressive reach. The relationship between antenna and ground is at best a very high impedance affair with little useful result.

A part 15 transmitter attached to a ground rod will tune-up beautifully on the output meter because the impedance between transmitter and ground is sufficiently reduced to provide a ground path to complete the circuit... except, that the highly resonant well tuned signal will be confined to an area near the ground rod and will not extend to the far field. In fact a ground rod is merely a negative dipole element buried in the ground where it loses potency.

Only ground radials will serve the radiated signal out to the distance by "claiming" the ground-plane and coupling it with the antenna system.

The final frontier amounts to trying different numbers of and lengths of radials.

Yeah.. The advatages appear

Yeah.. The advatages appear appear clear, though I've never tried it... Would have, but the bigger problem is actually having the patch of land to do it.

Thinking about building a big planter on the roof and installing the transmitter inside that, and running the ground wire thruogh an attached dirt filled pvc pipe leading down to the bottom.

Technically legal

No, I'm not serious.

Rich Powers Part15, Take 2..

Carl, have you been

Carl, have you been experimenting with an outdoor install?

Rich Powers Part15, Take 2..

Not Exactly

Rich Powers wonders:  "Has Carl been experimenting with an outdoor install?"

Only partly.

In the back of the house my Wintenna, a metal window plus added wire to achieve 3-meters, has a below the floor set of two radials, one going north through the basement, the other going south up into the outdoor yard. Very excellent range toward the south.

In the front of the building is another Wintenna with the ground clamped to the I-beam which connects to the water pipe ground and electrical ground, the field strength strong only local to the ground, Very little range.

The front system totally penetrates the whole building and the outside walls, but is very weak in the distance.

Carl Blare

Ground rod vs. radials

This has certainly been my experience. Right now I am at (20)  30 foot radials and it made a heck of a difference.

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

What Comes Next

The principles that I have claimed in this thread did not arise in my mind right away because I would have expected them to be more clearly spelled out here on the part 15 forums, but I don't recall that they have.

Both of my systems serve their own purposes...

The direct grounded transmitter completely covers the interior building and the outer walls of the building out to about 20-feet.

The system with ground radials penetrates the immediate neighborhood and is fully present anywhere in the yard which is very convenient.

What we wonder next is what would happen if both transmitters were

A.)  Equipped with a switch so as to have EITHER direct ground OR radials;

B.)  Be COMBINED to give both transmitters BOTH systems... would it IMPROVE the overall result?

We are guessing that any of those switches would require re-tuning everytime the ground system was changed.

Oh good, just what we needed... another project on the list.

Carl Blare

Ground radials

Carl,

Regarding ground radials, is there anyone of the opinion that more is not always better? I realize at some number you reach the point of diminishing returns. In my very limited experience I just know I saw a significan increase in range when I went from (10) to (20) 30 foot radials. I was considering adding another 10 once I get the xmtr setup finalized in the outdoor enclosure.

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

There was an interesting

There was an interesting discussion about this by several of the more knowlegable here a few years ago. You should find your answers in this thread:

Understanding Vertical Antenna Ground Radialshttp://www.part15.us/forum/part15-forums/antennas/understanding-vertical-antenna-ground-radials

Rich Powers Part15, Take 2..

Mysteries of Ground Radials

Jim Henry is in the lead:  "Regarding ground radials, is there anyone of the opinion that more is not always better? I realize at some number you reach the point of diminishing returns. In my very limited experience I just know I saw a significan increase in range when I went from (10) to (20) 30 foot radials. I was considering adding another 10 once I get the xmtr setup finalized in the outdoor enclosure."

As of now my 2-radials are the sum of my experience in the area.

And yes, Rich Powers, thanks for that link! I want to start reading and re-reading all the postings about ground radials, some of which (as I recall) are about part 15 installations and some are about amateur or full-power stations.

Jim, your findings contribute to the knowledge data base...

... and I am compelled to add a hunch:

Again, this is a hunch... I SUSPECT that the ideal number of radials might vary from one installation to another, which is probably obvious, but I also suspect that a given installation will vary because of ground conditions and climate changing over time!

Of course you can't instruct your radials to grow or shrink based on ground conditions, so at some point we must settle for a fixed solution.

Carl Blare

There is a very interesting

There is a very interesting report of a 1980 study concerning grounding and ground radials of outdoor transmitters (portable whip and mast type) on pages 57 thru 63..

Highway advisory radio operational site survey and broadcast equipment guide (Report - Federal Highway Administration ; no. FHWA-RD-79-87)

https://archive.org/stream/highwayadvisoryr00turn#page/56/

There's some curious things pointed out in this document.

 

Rich Powers Part15, Take 2..

Carl I always thought your Window Frame

antenna experiments were good because some Part 15 AM experimenters will never be able

to do an outside set-up in the

"middle" of the yard.  

At the other house, 

I was able to go outside with 

the set-up.  I started with 4 radials

and then 8 and then 16.  It was

interesting doing that and seeing

the range grow.  Some of my radials

were 10 feet and some 20 - - there were

lots of big rocks and tree roots in that 

yard.  Some of the radials couldn't go

very far.  The AMT-3000 was inside a

children's playhouse.  The 9.5 foot stick 

was attached to the outside of it.

Brooce Part 15 Hartford

 

NOISE AND STATIC RADIO

Ideally a radial would be 1/4

Ideally a radial would be 1/4 wavelength. I noticed as my radials degraded, so did my signal. It'll jump up to its normal range when it rains but as soon as the soil drys the coverage will drop dramatically. When the radials were good there was no difference between wet soil and dry soil as far as my signal was concerned.

For what it's worth, the

For what it's worth, the study conducted by the Atlantic Research Corporation for the highway department concluded the following concerning legth and number of radials (from the above linked document):

"... It may be observed that the resistance (which is primarily ground resistance) does not change appreciably with radial length, but changes significantly when the number of radials is changed. In fact, a single 1.8 m ggground rod at the base of the monopole gave lower resistance than did the use of only two ground radials.

It is probable that the multiple grounding points resulting from pinning the ends of the radials to damp earth had greater effect than the lengths of the radials.Antenna capacitance may be seen from Figure 20 to increase with either length or number of radials...

..Model results show that with eight radials, capacitance does not increase with radial lengths greater than the monopole height. Radiation resistance increases rapidly up to radial lengthsequal to monopole height, and very slowly as radial lengths are made longer.

Data on numbers of relatively long radials (3.4 x monopole height) show a 21% increase in capacitance going from two to eight radials, a 4% increase going from eight to 16 radials, and only a 2% increase going from 16 to 32 radials.kRadiation resistance varies very little above eight radials.

Based on the preceding measured and model data, the following recommendations can be made with respect to the design of a radial ground system for HAR monopoles.

1. Length: At least twice the monopole height.

2. Number: At least eight.

3. Material: No. 10 or 12 AWG bare solid copper wire has proved effective.

4. Configuration: Symmetrically arranged in a circle if practical. However, the pattern may be altered to fit space available without appreciable loss of coverage. For example, a "bow-tie" configuration might be used to fit a restricted highway right-of-way.

5. Burial: Burial to a depth of .5 m to .75 m is recommended both to protect from damage and to provide good earth contact. An alternative when concrete or asphalt pavement makes burialdifficult is to drop the radials into shallow slots cut into the surface, and to connect the ends of the cable to ground rods driven into the earth.

///So this appears to conclude that longer the radials, the better.

 

Rich Powers Part15, Take 2..

Radials, number, length, and effect on range

Rich,

Good info, thanks. I have not yet read that study yet. When I went from 20 to 30 thirty foot radials I was able to reach out 9,000 feet on the south side of my antenna. One thing is puzzling to me is that 9000 foot was on the other side of the hill I am on. My home is about 875' above sea level and about 160' above street level. The antenna is mounted in my back lot and that is at the level with the 2nd floor of my home, BUT, it is still about 100' below the very top of the hill.  The audience I want to reach is not in that direction but rather to the north, NE, and NW of me. I was getting about a mile in those directions. BTW these results were when testing and running through about 150' of coax from xmtr to antenna. I know that's not in compliance, was just for initial testing,  and the xmtr is shut down now while I get it ready (almost done) to eliminate that coax run with the xmtr mounted on the antenna. My soil is very rocky with just about 6" of topsoil above what seems to be bedrock granite in most places, so I expected to have ground challenges.  I expected to have to use bare wire for the radials but was told that STP would work fine. That's what I used and it does seem to be fine.

Jim Henry HBR Radio 1610, serving Honey Brook, PA. and NW Chester County.

 

 

"..I was able to reach out 9,000 feet on the south side of my antenna. One thing is puzzling to me is that 9000 foot was on the other side of the hill I am on.. ...antenna is mounted in my back lot and that is at the level with the 2nd floor of my home, BUT, it is still about 100' below the very top of the hill.. "

This is just an assumed guess, but maybe the improved range on the hill side has something to do with a higher collection of moisture content collecting at the bottom of hills, and since your antenna is below the hill, there is thus better ground wave propagation there.. I don't know how scientific or accurate that assumption might be, but it's what first came to my mind.  

I get the impression.. based only upon years of periodically reading about ground radials -- so I can't genuinely give personal experience know-how advice about it, cause I've never done it...  But my strongest impressions causes me to conclude that biggest catalyst for making a ground radial system most effective, is not only having an equal multiple of radials, but also perhaps more importantly having ground rods at the ends of several of those radials.

This was mentioned in the above: ""It is probable that the multiple grounding points resulting from pinning the ends of the radials to damp earth had greater effect than the lengths of the radials"

And of the top of my head, I recall similiar emphasis about using multiple ground rods is found in some of the Hamilton Rangemaster documents, for example:

"What you are trying to do is make an electrical connection to the earth over a broad area. What that means is if you have multiple rods keep them at least 6 feet apart, don’t concentrate on just a small area of dirt. For example don’t place 10 rods in a 2 foot circle.  The more yard area you can cover with your system the better. A 20 foot diameter circle would keep the rods about 6 feet apart. Keeping the system spread out allows the currents to flow more efficiently." http://www.am1000rangemaster.com/amradiogrounding.pdf

I suppose your bedrock lawn isn't helping anything, and driving additional rods may not be feasible in your situation, but it does illustrate the point that the key objective is to bond with as much ground area as possible

 

 

Rich Powers Part15, Take 2..

i read plenty of old tech

i read plenty of old tech books and what i remember is that once you go past 36 radials its diminishing returns. the radials act as a ground plane for the antenna and thus behave as part of the antenna. ground rods dont do this. i did however see some benefit to dropping a ground wire down an unused sprinkler well.

Legality of Elevated Radials?

All this talk about radials has me wondering (again).

As you all may know I have an elevated Procaster that's been on the air nearly 4 years now.  I run it with no ground connected at all, due to the limitations on ground lead length (even if I didn't have an antenna at all, I'd still be over the limit on the ground lead alone).

But I have from time to time wondered about elevated radials. 

I have seen reference, over the past few years, to the concept of elevated radials, either connected to the transmitter ground itself, or the suggestion that a roof mounted transmitter with the ground lead being a short wire connected to a metal roof would be both effective and legal. This would imply that connecting the ground lug to my metal gutters would create a legal, horizontal, ground plane of sorts. It would be interesting to try it and see what field strength changes to.  But would it be legal?

Whether of not this would greatly benefit my operation, I don't know as I cover my small town just fine.  It doesn't take much, in an area with a very low noise floor, to cover 4 blocks wide and 1/4 mile long, when I'm in the middle of it!

My curiosity more leads to legality. We all like to believe that horizontal radials don't radiate, and are thus legal.  The ARE they? I don't believe there's any documentation or inspection paperwork, showing that a transmitter with a 3 meter antenna and horizontal ground leads will meet the legal requirements of antenna + ground lead equaling no more than 3 meters.  I'm suspecting that the length of all the elevated radials combined would wind up gounting as "ground lead". I would not try this unless I had some hard evidence that it would be considered legal.  As you may know I try to run my operation as blatantly legal as possible.

Anyone have any hard evidence on legality of elevated radials, etc?

TIB

Well, if you want to be picky

Well, if you want to be picky, there's no hard legal evidence that attaching a short ground wire to a long metal mast is not OK.  Nowhere in the rules does it state that a ground can't radiate.  And in fact, FCC inspectors used to interpret the rules reasonably strictly, allowing short ground wires to large metal objects.  That has obviously changed in recent years.

IF, and it is a big if, the intent of the FCC is to not have a long radiating ground, then elevated radials should be OK, as long as they are 180 degrees apart, strictly perpendicular to the antenna, and each the same length.  You'll get no radiation, just an increase in antenna efficiency.

If those radials are sloped, however, you will get a marked increase in radiation.

The FCC inspector has the final say.  I'm not sure that you'd know for sure until an installation that had similar radials was inspected, and passed.

Conclusions Reached

I have recently gone in print to debunk the notion of "long ground lead".

It seems obvious and logical that a vertical wire below a transmitter that has a vertical antenna above the same transmitter is not a ground lead but is in fact the negative leg of a vertical dipole antenna. As soon as the sum total of vertical antenna wires above and below the transmitter exceeds 3-meters it is not FCC compliant.

Calling it a "ground lead" is erroneous.

Horizontal radials are not "ground leads" either, so long as each radial is matched by an equal length radial in the opossite direction putting the two radials out of phase with each other.

I strongly propose that radials must exist in opossing pairs so as to null-out any possible radiation by being out of phase with each other. Only even-numbers of radials meet this standard.

Because bonafide radials are not "ground leads" they are in fact ground itself... made more obvious if melded with the earth, but when elevated above the earth would be known as "virtual ground".

I have not encountered any FCC documentation either supporting or otherwise discussing these principles.

Carl Blare

That's a good point Carl.

That's a good point Carl. And so is Artisians.

Rich Powers Part15, Take 2..

If you want to be 100% by the

If you want to be 100% by the book you would have a 2 foot antenna and 3 ground plane radials.  in essence what you would have would be the equivalent to a CB ground plane.

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

http://thelegacy.shorturl.com

More Power for Hobby Broadcasters

http://the-initiative.boards.net/

The point is that there is no

The point is that there is no 'book' describing radials, elevated grounds that don't radiate, etc.

You're entirely at the discretion of the FCC inspector.

Discretion is Dangerous

And this is exactly why I've never tried it or experimented with elevated radials. My goal is to always be blatantly legal. Which is why I was wondering if there was any precedent for elevated radials. 

I don't really experiment at all with my station, as it's been on 24-7 for almost 4 years and I actually have regular listeners. I don't want to screw with it when people are listening.  Experimentation would require a second transmitter on a different frequency.

TIB

Legal Blatancy

Beyond what the rules say in the literal sense I suggest that "discretion" is not always dangerous if solid physics are on your side.

All of us seem to agree that wires that radiate are necessarilly measured by the meter and anything that doesn't radiate can be called by any name you prefer, e.g., "ground lead" "negative leg of dipole" "virtual ground" and literally is a matter of REASONABLE discretion.

Radials that don't radiate are safe territory in the realm of logic, the thing to fear is an agent who acts unreasonably, for whatever reason.

Planning our lives based on fear of what rogue officials might do is akin to paranoia.

Carl Blare

The problem is usually

The problem is usually because our gound leads do radiate due to our short antennas. The FCC has never been very clear regarding the use of top hat capacitance but I swear I've seen them tag elevated radials. You essentially turn the setup into one large dipole antenna which would count towards total antenna length. Tim has about 2 feet of wire he could play with, I'd venture to guess that 2 feet of dangling wire on the end of his procaster might actually help out that signal just a touch.

properly setup elevated ground radials

do not radiaite even with an electrically short antenna.

problem is all the radials must be the same legth and have another radial 180 out of phase with the other and they can't droop must be perfectly horizontal.

this is not easy to acheive in an elevated install but not impossible.

an example would be such a radial system laid out on a flat city building or apartment building roof.

Part 15 Engineer

Hindsight is 2020

I'm not a democrat or a republican, i'm a common sense moderate progressive

 

please don't forget to register and vote

Tim

Tim

if you have the clearance inside your attic for the 3m whip then placing the procaster inside over a symetrical ground plane laid out on your attic floor would be legal as it should not radiiate in this case and they would be perfectly horizontal. but you must take great care to make the radials symetrical.

 

as long as you have a shingle roof (no slate or aluminum) with wood sides it will not hamper your signal any.

Part 15 Engineer

Hindsight is 2020

I'm not a democrat or a republican, i'm a common sense moderate progressive

 

please don't forget to register and vote

Equal But Opossite

Part15 Engineer said:  "problem is all the radials must be the same length and have another radial 180 out of phase with the other and they can't droop must be perfectly horizontal."

That got me to thinking about radials on the earth.

The earth is not level in all places, so radials might end up not being perfectly horizontal.

In fact Jim Henry reported a finding that I also noticed, being on the side of a hill the upward pointing radials actually push the signal uphill and over the crest of the hill to the area beyond.

The other problem, keeping radials exactly straight in the air has got to be a difficult physical task with wind blowing and birds landing.

Carl Blare

I can relate to the

I can relate to the discussions of imperfect terrain.

I have yet to get an antenna designed for my Chris Cuff C-Quam Stereo Transmitter.

My yard is mostly ledge rock, with top soil placed on top of it. Those ledge rocks stick up in a lot of places. I can't very well place a 10 foot antenna in the middle of the yard, because I rent and have other tenants who use the yard.

Although I could go ahead and do an install in the middle of the back yard, I think that is impratical for the others who live here.

I have trees in the back yard, a little piece of land that is still uncleared of trees and wild brush (wooded area), but those trees are so close together, they are basically catapults sticking up in the air. They sway something terrible in the wind. I can't imagine even placing a wire onto one of them, the trees would sway to the point that the wire would be pulled and loosened over and over again, also it's impossible even to get a wire up to the point where the trees have branches. Like I said those trees are basically sticks sticking 50 feet up with branches and leaves way up at the top portion.

I have one lone tree in the yard, that has potential, it has grown quite tall, however it has many branches and leaves and if I am not mistaken, those act as negative deterants to the signal.

I suppose I could place a long pole below the antenna to get the actual antenna above the highest branches, but then we have another issue with an antenna swaying in the breeze, even worse if there is a lot of wind.

I am on a hill, with a slightly inclining and declining terrain running west to east, so basically I am on the side of a hill at an elevation of 156 feet according to Google Earth the highest point to the west is 175 feet. Then of course you have to factor in trees and buildings surrounding my house and the highest hill is to my east which is 190 feet and is roughly 0.08 miles from my house, to add insult to injury, there are 3 story apartment buildings lined up along this long hillside.

Soooo, my project continues to remain on hold as I ponder and ponder and ponder what is the best way to go. I could go with a roof install on the smoke stack, but I currently have UHF television antennas on that for OTA TV and a scanner antenna mounted above those.

This antenna lengh restriction of 10 feet also make it difficult to simply string a wire  horizontally from tree to tree out of the equasion, since the wire length would end up being over 10 feet.

So, I am faced with two obsticles, ledge rock and no place reasonable to place a ground mounted antenna.

Ponder...ponder...ponder...ponder....

To Be Continued..........

Bruce.

Terrain Isn't All It Appears

This posting is inspired by the recent post from Mr. Bruce

With the question of "imperfect terrain" I have already decided that my earlier impression of AM antenna locations is inaccurate.

Like many radio buffs, which means radio lovers undressed, what I think I see standing as I do on the earth, may not be any kind of an accurate representation.

Land slopes upward, downward, there are crests and nulls in land distribution but viewing it from ground-level is not accurate. Everything is "downward" from our gaze because we stand around 5-feet tall. "Uphill" might appear to simply "meld into the distance" where the trees are tall.

Beethoven understood this when he wrote his string quartet Opus 130.

And when you think about it, we are condemned for infinity to come always to ground and length because they are central to part 15, unlike the problem of Trump, which opens concerns of White Nationalism, racism, criminal hate and program content.

That is why I think the earth is not flat and Aijet Pai is wrong.

Carl Blare

elevated radials

The only reason why the elevated radials of a vertical antenna that has no matching network (like CB antennas) are horizontal to the ground is to provide a 50 ohm impedance match to the feedline. Having them droop only results in raising the feedpoint impedance. And yes, they radiate even when horizontal.

mike

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