For the longest time have been trying to figure out how I can NOT have my transmitter on the roof of my location. it’s only a single story, and a problem might never ever even arise because of it.. But there’s always the ‘what if..” and Murphy’s Law.
So the hope and goal has always been to try and make certain the install is completely FCC compliant.
And the best option is a ground level install – right?
Right.
Now here, in no particular order, is what I understand to be the most important objectives concerning ground installs for Part 15AM (correct me if I’m wrong)
1.) It’s most effective to have it in the open and away from any tree or obstructions, and definitely should not be installed close to the wall of a building.
2.) Numerous buried radials in the longest feasible length should be employed, fanned out from a central location directly under the transmitter with a 8’ ground rod, and also rods attached at some of the radial ends.
3.) Uh.. see objectives 1 and 2.
OK.. well, I really don’t have the land available to do that; I’m surrounded by sidewalks, streets, and buildings.
But upon seeing this drawing: http://www.mobileers.com/Images/TowerRadialJPGa.jpg , I realized how similar a situation that ham operator has to mine.
The biggest difference (that I see) is that he’s connecting to tower antenna, and I’m connecting to a Rangemaster with a 3 meter whip, which would place it against the wall, but I would probably be able to install about 15 foot or so from that wall, – But the question is could his method work well with my little transmitter even though it appears to contradict objectives 1 and 2 listed above?
What I’m saying is I would be able to set up my ground system very similar to the way he diagrams in his drawing..
But with my whip that close behind a building wall,and below the roof could it still result in good performance?
Any comments?
By the way that drawing is from “An Easy Way to Install Ground Radials” by Brian, W9HLQ at: http://www.mobileers.com/chiGroundWires.htm
An aerial view of my location is http://goo.gl/maps/2ZWZX
I think the answer is … it
I think the answer is … it depends.
First, I wouldn’t get all that hung up on an elevated install. You do have the ground wire issue, but Lefty Gomez has described his installation, and he actually obtained better range by disconnecting his ground wire from a Talking House ATU mounted reasonably high.
It has to be realized that there is nothing inherent in the FCC rules that states that you cannot have an elevated installation. Particularly if you are using an FCC certified transmitter and are installing it according to the instructions (which form part of the certification) – examples include the Talking House & ATU combination, the Hamilton Rangemaster, the ChezRadio ProCaster. You need to follow all the other restrictions in Part 15, but then, you obviously know that if you’re asking these questions.
The biggest problem with a ground level installation is obstructions, as you have pointed out. Buildings, trees, etc. will absorb your signal. However, you can have a much better ground system (in some cases, just a ground system), which increases your antenna efficiency, and therefore signal strength.
With an elevated installation, you can get above a lot of obstructions and reduce the signal loss. However, your ground, if you have one at all, will suffer, which will reduce your antenna efficiency and reduce your signal strength.
I don’t think that there is any easy answer, as it will depend on your geographic locale, what obstructions are near you(including what they are made of, i.e. wood, metal, etc.) and even the type of soil you have. I suspect all you can do is try both types of installs out, and see which gives you the better signal and range.
As an example, I used a Hamilton Rangemaster ground mounted in my previous location, which was relatively in the open. My ground was just a steel mast pipe pounded into the soil, but that soil is part of a river flood plain, so it makes an excellent ground. I got a great signal.
In my current location, I’m surrounded by trees and big houses. I tried the ground mounted installation but the signal and range was pretty poor, even with that good soil. I got an OK signal with a ProCaster slightly elevated, and a short ground lead to a gutter. But the best signal has been obtained by elevating the ProCaster to well over the tops of all the nearby houses (and most of the trees) in the area, no ground lead.
Your results may vary.
Radial Beliefs
I believe that for every ground radial that goes in one direction, there needs to be an equal but opposite radial going in the other direction, or the un-opposed radial will probably radiate and add to your field strength.
I looked at the link Rich Powers provided up above and see that the radials in the particular installation fan on only one side of the tower.
I think to make that radial system balance each radial that stretches into the yard needs an opposite radial that goes into the basement of the building and is strung along the ceiling until the correct length is matched.
I know Rich Powers that you have talked about this in the past, but the subject is being reviewed so let’s cover this again….
Is there any hope of centering the antenna on a flat roof and fanning radials on the roof?
I should go look at the Google over-flight of your building. Here goes…
I’m back. I can see what a prime location you have, and it sure seems like an elevated antenna would be the best choice, and you know….
I realize that editorial commentary is not welcome, but I can’t seem to hold back….. this is a chronic problem in part 15 and when I said that the rules are anti part 15 hobby this is a perfect example….. there is no effort nor thought given to this inevitable situation of needing an elevated antenna WITH grounding. It’s needed.
And we are further hampered by the sense that a member or so will report any admissions of having an elevated grounded system.
Part 15 is being damaged by the status quo with the unsettled ground issue.
I’ll now leave the room in a huff and stew somewhere.
Plan of Action
Elevated transmitters are not my own personal concern, I am not trying to reach a large area. But I realize that circumstances arise when the only choice available to a part 15 transmitter installation is indoors, or up in the air.
I cannot think of a more nagging problem that has plagued the growth of part i5 than the elevated antenna problem, in particular.
And by coincidence we have a sniffer who stands guard to be sure vertical ground leads are quickly ruled out.
This is a problem for the ALPB. At the next meeting I shall present to committee the unsettled question of elevated ground connections.
To be told, “Just don’t have a ground for elevated installations” is not an answer, not a solution, and is bad advice.
The Mission of the ALPB is “to improve radio broadcasting…” Therefore it is entirely appropriate to formalize a discussion of how we can do that in the real world, and this ground thing makes the perfect test case to see whether the Organization can in fact influence true improvement.
Rich Powers, the ALPB is our only hope.
Constructing and installing a
Constructing and installing a non radiating ground on an elevated installation would be a great subject to explore in the ALPB. Because that’s really the intent behind limiting the size of the ground wire + antenna + feedline – to limit the length of the radiating elements on the transmitter.
Example
The Isotron is one example of an antenna system which needs no ground wire or ground radials, which fits the bill for elevated systems or systems set up where dirt ground is out of reach.
They are incredibly easy to construct and not all that different from a loaded 3 meter rod with a cap hat and radial system.
RFB
Obstructions
In early summer I installed a ground mounted system on the edge of a wooded area with trees and honeysuckle very close to the antenna. Monitoring the field strength shows no difference between the strength during the summer and now when the leaves are gone (except for an increase after rains). If there is an effect I have not been able to measure it. Despite the placement of the antenna the observed range is from 1 to 2 miles which seems to be very good for part 15 AM. It is possible that the range has changed but I don’t have enough data to conclude this.
Placing the radiator next to a wall may result in some detuning which can be compensated by retuning the loading coil network. This may also present some capacitive coupling to ground which can reduce the radiated signal but if the separation is several feet this should be minimal. The presence of the building will not block the signal at AM frequencies and produce a shadow providing the building is small compared to a wavelength.
I was unable to view your location via the link but I suggest you try a temporary setup using radials placed on the ground. This is what I described here and it gave good enough results that I made a permanent installation with buried radials.
If you find it easy to try a temporary setup as did I then you will know if it is worthwhile to make it permanent.
Neil
There always seems to be a
There always seems to be a creep up of contradictions with this hobby.
This source emphasizes an increase in range for part15 relies on ground wave more than skywave:
“Listeners tuning in to low power AM broadcasts are usually receiving our ground wave rather than sky wave so better ground, more ground wave…” http://lowpowerradio.blogspot.com/2012/05/low-power-am-broadcasters-can-improve.html
Yet a great deal of sources, including the manufactures emphasize to get the transmitters up high for best range.
The latter makes more sense to me, but I’m neither well versed or an engineer.
But regardless of which way works best, I just want to feel secure it’s legal.. don’t want to get everything going full stream and worrying about a risk of being shut down for noncompliance.
If mounting high without a ground is the way to go, I’ll do it.
Yes I could lay radials on the roof under the transmitter, but from what I understand, that method would be questionable.
Installing per the manufactures directions is also apparently questionable (as several NOAA’s have shown)
The Isotron is interesting, but I prefer to use the whip to maintain the transmitters certification.
And laying down radials at my location for ground install as just a test would not be so simple due to my situation.. I don’t have the room, the only way would be by mimicking the method shown in the drawing posted earlier in this thread.
It feels such a long unending circle of speculation and contemplations with no foundation to grasp and act upon.
Nevertheless, I do appreciate all the inputs.
Ah, what to do, what to do..
Uhhh…. I meant NOUO’s not
Uhhh…. I meant NOUO’s not NOAA’s
An Invention in Mind
I opened up an extra 1% of brain power and may have come up with the solution to elevated ground leads.
I hope some of our resident engineers will present some thoughts on how to achieve this….
What I see are two side-by-side ground leads from the elevated transmitter down to the ground-rod exactly 180-degrees out of phase with each other to cancel out any radiation.
I’m guessing that either a toroid transformer or special solid state circuit would be employed to create differential ground connections at the transmitter, a push-pull ground, in effect.
I have a second proposal to present following discussion of this one.
Got It
I’ve figured it out.
Here’s the deal……
An unbalanced to balanced toroid balun with one primary and double secondaries will provide all the wires and phasings needed to achieve what I have proposed.
From there, you should be able to use your imagination to visualize how to wire it.
Viola. An elevated transmitter with ground is now a possibility under the incomplete part 15 rules such as they are.
Thank you’s will be accepted in the form of bakery products or canned fish.
Said Before
“An unbalanced to balanced toroid balun with one primary and double secondaries will provide all the wires and phasings needed to achieve what I have proposed.”
Now your talking…and thinking. I proposed that approach some months ago right here at Part 15.us. But that was immediately shot down by a few.
I have already tried it and the balanced ground path does null out any radiation that would come from a single unbalanced ground “lead”..or more accurately put…ground path.
However the converting to balanced puts a bit of resistance in the ground path from the toroid windings themselves. But not so much as to put the concept in file 13.
It was a slap together toroid. 25 turns x 3 T50 core. Worked really well at a height of 20 feet.
Before the nth degree’s start spouting..like I said, it was a quick slap together experiment.
My next experiment with that toroid is to turn it into a combiner to take 4 100mW transmitters and combine them into a single 3 meter antenna.
RFB
Great
Perhaps when you posted that experiment I simply wasn’t grasping what was being said.
Very excellent, RFB!
We’ll call it “The RFB Ground Elevator”.
Too bad I can’t try one, but I will not have an elevated antenna.
Maybe Rich Powers, if you want to give it a try, we could get a report.
I’ll count to 1,872, then describe another “raised ground” scheme that I have in mind.
A Few Comments From Bruce
I am very interested in the tech
experiments you guys have posted
just recently.
As you know, I am trying to complete
a bunch of Part 15 experiments before
we move.
In addition to some that I have worked
on in the last few weeks, I am going
to try to make a Part 15.219 “transportable’
package that can be taken somewhere and
deployed, used, taken down easily, and
then stored until you want to use it
again.
Let’s see how this goes.
By the way, I had a ground mounted Part
15.219 set-up about 10 feet from my house. It got
a long way, which isn’t too bad because
it was not optimized. Even the transmitter
wasn’t the best. It was a Ramsey AM-1
modified for crystal control.
I heard it about 1 mile away on the car
radio. More local coverage was hard
to figure out, because I wasn’t going into
neighbor’s houses to check the signal.
But it didn’t do too badly. With a better
transmitter, it would have worked out
much better, probably.
Also, it coupled to a lot of the power lines
that were out on the street, which made it
louder in some places. (It was not near
the house power line!)
For whatever it’s worth.
Bruce, Carrier current and 13.560 MHz
experimentation
A New Approach
I just realized that the balance resistance issue to the ground path could be drastically reduced by using a tapped toroid transformer. Instead of 3 isolated windings, only 2 would be needed and the ground connection from the TX taps the bifilar windings at the center of the winding.
RFB
I realized a long time ago
I realized a long time ago that when knowledgeable experienced individuals express technical matters about engineering, It causes my mouth to drop in a stunned and dumbfounded manner.
I like to put honey on my Cheerios.
(spoken awkwardly for lack of an appropriate response)
i wrapped my ground lead
i wrapped my ground lead around a toroid right near the transmitter ground lug. my lead is about 8ft to ground (2ft ground rod about 1.5ft in ground) and a 10ft radiator. it is the best i am able to do. i also put 3 snap on ferrite cors on my audio and power leads to minimize radiation from them as well. it will be the amt5k i will be running. if we can figure out how to do a 180 deg phased ground lead that is easily replicable i will attempt that in a twisted pair config. i am in an apartment and am very limited in what i can do here by the landlords and my location.
i wish i had an fcc contact i could run this scenario by i would feel much better knowing how it would be interpreted by an inspecting agent. wish i had thii ver5 & external atu. i could run it minus ground lead and have enough range from it to cover complex.
Choking Return Path
“i wrapped my ground lead around a toroid right near the transmitter ground lug.”
Problem with that is your choking off the return path for the RF back into the TX. Like only attaching the positive side of a voltage with a fat resistor on the negative side. Doesn’t make for a good completed circuit.
And the choke at the TX ground lug doesn’t resolve the length issue..ie 3 meter limit of antenna, coax, ground lead.
KENC is the perfect example of how the choke did nothing to prevent the shutdown due to the exceeding 3 meters.
“if we can figure out how to do a 180 deg phased ground lead that is easily replicable i will attempt that in a twisted pair config”
Already done that using a toroid. Next experiment is to try it with a bifilar winding toroid and tapped to produce the 180* phase shift.
RFB
I Have To Really Understand This
Meanwhile, honey really does taste good on Cheerios.
Bruce, W 60 HZ, X-13
Honey with Grounds
I stir honey and cranberries into 100% whole grain oatmeal during the cold six months of the year.
Good grounding is better as a summer project when the earth is pliable.
Good Beezness…
Honey is a good antibiotic also.
Old TV
I always thought the old TV show “The Biotic Man” was kind of silly, but now biotic men are in our midst.
Anti-Biotic?
Pass the cherios…
Balancing out Ground Lead Currents
Carl commented “What I see are two side-by-side ground leads from the elevated transmitter down to the ground-rod exactly 180-degrees out of phase with each other to cancel out any radiation.”
Assuming I understand the proposed use of a balun to provide equal and opposite currents in two adjacent ground leads here are some observations.
Where do the equal and opposite currents go? Current going down one line would need to be turned around so it can flow up the other line. This could be done by connecting both lines at a point on a ground stake and the two lines together would be acting in differential mode with equal and opposite current in each line.
But this does not solve the fundamental problem with a conductive path from the transmitter ground to earth ground producing radiation. This is due to what is called the common mode current which is a current in each line which flows IN THE SAME DIRECTION and doesn’t cancel line to line. This is the current which is collected by the ground stake and is returned to the transmitter plus the current which is coupled from the radiating element to the ground lead. As the current in the antenna is pushed up by the transmitter the current in the ground lead is also being pulled up so they are in phase. A connection from the transmitter electrical ground to the earth ground will have this common mode current as will a length of wire which is connected to the tx. ground and left unconnected at the ground stake (it acts like the other leg of a dipole).
Neil
Elevated Radials
In previous postings I think it was fairly much agreed that elevated radials are a realistic solution, although perhaps physically very challenging depending on the roof configuration.
It would appear that the bluntness of physics is standing squarely in the way of part 15 AM being easily applied by certain users.
Efforts must be directed toward modifying the laws of physics.
Efforts must be directed
Efforts must be directed toward modifying the laws of physics.
LOL