I am including the following text taken from the Rangemaster website for this thread (hope you don't mind Keith). I tend to agree with Keith's interpretation based on the fact that there is a safety issue here regarding lightning protection. What if somebody was injured by lightning entering a home because they were afraid of grounding their equipment properly? If you look at procedures for outside 802.11 wirless LAN setups, the gounding is of paramount importance and not to be taken lightly.
Furthermore, I do believe that this church grounding issue was because of a complaint. Somebody likely noticed the range of this transmission and reported it. People don't seem to realize that their radio AGC was likely up at maximum and that the effective signal being transmitted was in fact a very weak signal and of no threat to any commercial station.
Gerry
"There are a lot of questions about whether or not the ground wire is to be included in the FCC 3 meter limit. I have discussed this with the top FCC enforcement official in the DC office. He has told me that the FCC gives the designer latitude to determine what ground is as long as it is reasonable. We have no problem calling the tiptop of your ground wire at the transmitter binding post "ground" as long as you use a massive wire, (#12 or #10) intended for grounded purposes. Click the following for further discussion.
We do not feel that in this case the Ground cable is included in the 3 meter limit...
Regarding the "ground" issue we at RangeMaster feel that after reading the Part 15 rules and discussing with officials at the FCC that all ground does not have to be dirt, for several reasons:
What is ground isn't specified in Part 15, just the antenna and ground LEAD length.
It is just impractical for all Part 15 transmitters to be located on the dirt. In most major metro areas, close access to the dirt just isn't practical. For many reasons (vandalism, traffic, local regulations, safety, ect.) It is reasonable to allow the installer some flexibility in location for the Part 15 transmitter installation. The most out of the way location is typically on the roof.
The most important reason we suggest people be able to ground their transmitters to a ground other then the dirt is lightning protection. The lightning protection provided by lightning protection circuitry in our transmitter is critical to protect life and property and must be ground properly to provide such protection. What we don't like to hear (and do often) is customers in apartment buildings who do not have their transmitters grounded at all and have had lightning damage because they are afraid of the 3 meter rule, they didn't follow our grounding instructions because they have been told by someone that it would violate the 3 meter rule. This is an unfortunate situation.
In our discussions with the FCC massive metal that is connected to the dirt, such as a water pipe, can serve as an acceptable ground. I have been told that the FCC generally won't interfere with a site engineers decision (if the site engineer decides to call a water pipe ground) unless the decision seems outlandish. We feel a large piece of wire, coming up from the dirt can also be called ground at the top tip. As long as the wire takes a direct path straight down to the dirt, this is best for lightning protection. We have had this set-up pass FCC field inspection many times. If there is a concern about the wire adding extra radiation the wire could be encased in an electrical conduit, grounded at the ground end only. We don't feel that in most cases, a properly designed ground system will add significantly to the overall radiation of the system, however if your system requires it, we stock an RFI filter that you can place in series with the ground terminal of the transmitter (needs to be placed physically right at the transmitter ground terminal to be effective) that will suppress RF radiation from the ground system. Just let us know when ordering and we will include the filter."
Gerry: "I do believe that this church grounding issue was because of a complaint. Somebody likely noticed the range of this transmission and reported it."
Physics shows that a ground wire or any assembly of "leads" and/or conductors of ANY gauge will radiate when connected together between the tx ground terminal and the true r-f ground reference (ground rod, water pipe, radials etc). In virtually all cases it will radiate much more field than the 3-meter whip above.
The length of the conducting path to r-f ground was the basis for the church citation, but the underlying reason for limiting the length of that conductor in the first place (15.219) was to limit the radiation possible from unlicensed AM systems.
Now following with comments to some of the statements in your post, reportedly from the Rangemaster site:
Rangemaster "We don't feel that in most cases, a properly designed ground system will add significantly to the overall radiation of the system, ..."
There is abundant evidence in antenna engineering textbooks and elsewhere to show that radiation from a long conducting path to ground is a significant, and often the largest source of radiation from a Part 15 AM antenna system. If the meaning of "a properly designed ground system" as used in the paragraph above is one where the total radiating length of the conducting path to the buried r-f ground plus the length of the whip is 3 meters or less, that should be stated. But I don't think that configuration is described elsewhere on the Rangemaster site (correction invited). The installation drawing on the Rangemaster site shows the tx/antenna installed on a rooftop, with a long ground conductor.
Rangemaster " We have no problem calling the tiptop of your ground wire at the transmitter binding post "ground" as long as you use a massive wire, (#12 or #10) intended for grounded purposes."
Rangemaster may not have a problem with thinking of the top of a "massive wire" as ground, but that concept is not supported by physics. Even though the top of such a wire may be near "ground" potential for direct current, it has considerable resistance to the flow of the r-f energy in it, that results from the coupling of the wire with space, ie, because it is acting as a radiator. So the top of that wire is NOT an r-f ground. The whole length of that "massive wire" radiates until it enters the physical earth.
Rangemaster "..however if your system requires it, we stock an RFI filter that you can place in series with the ground terminal of the transmitter (needs to be placed physically right at the transmitter ground terminal to be effective) that will suppress RF radiation from the ground system. Just let us know when ordering and we will include the filter."
The r-f filter is good, but how are users to know whether or not it is needed? That takes an understanding of antenna systems that few Part 15 operators would be prepared for. And how about r-f filters for the power and audio leads -- they also will radiate unless filters are installed in them.
These quotes reportedly from Keith Hamilton/Rangemaster use phrases like "we at Rangemaster feel," "we do not feel," "we have no problem with", "it is reasonable to allow," "will add significantly," "and "I have been told." Such statements shift responsibility for using the information they apply to back to the reader, and wouldn't give anyone implementing such advice any reliable relief from possible FCC action.
Please note that I am neither anti-Rangemaster nor anti-Part 15. I am neutral. The purpose of my posts is to supply technically valid information to be used as its readers see fit -- which should offer a positive and encouraging benefit to those wanting to better understand Part 15 systems.
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Rich made the following two comments about ground leads.
There is abundant evidence in antenna engineering textbooks and elsewhere to show that radiation from a long conducting path to ground is a significant, and often the largest source of radiation from a Part 15 AM antenna system.
The purpose of my posts is to supply technically valid information to be used as its readers see fit
Theory and computer models are good and necessary. However, we all know that practical installations don't always fit the computer model. What would be good to see are some actual RF measurements from a test setup with different ground leads, to measure the RF current in the ground lead.
Very good comments Rich, especially about the audio and power supply leads; RF-wise, they are all radiators. Maybe the way to "live with" the FCC rules is to use some common sense and also be prepared to take some risk. We have seen that the FCC do allow installations which run against their rules to some degree. If installations "appear" to be conforming, the FCC agent may deem it OK. If the agent sees a long visible ground lead, he may take exception.
I cannot locate the website, but this site mentioned a Part 15 radio on top of a big metal billboard advertising for a car dealership. Somebody posted this site because they were annoyed that this might be a violation of FCC rules and went on to say that the FCC agent was informed and came to check out the transmitter and found it to be in compliance. They also went on to say that it was audible over a considerable distance. In this instance, the FCC agent obviously had no issue with the metal structure of the billboard being a "ground lead". The only difference between this installation and the church in question is a "lead" versus a "mast".
Here's a question: If a transmitter is installed on top of a metal pole (say 10 or 20ft) and grounded to the top of the pole and the bottom of the pole is placed in earth ground or connected to earth ground through a thick cable that was not visible, do you think this would be acceptable?
"mojoe" wrote: What would be good to see are some actual RF measurements from a test setup with different ground leads, to measure the RF current in the ground lead.
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Note to those with the instrumentation/skills needed to measure the r-f currents on the ground conductor(s)/power/audio leads of an elevated Part 15 AM antenna system... it is not just the magnitude of those r-f currents that is important to "coverage," but also the length of the exposed conductors along which that r-f current flows.
The longer those conducting paths, the more field strength they will produce.
It is certainly true both in theory and practice that an "elevated" Part 15 AM tx+3-m whip used with long conducting paths to a real r-f ground will have greater coverage than when installed on/near the earth.
But the reason for that is the added radiation from the long ground/power/audio conductors of such systems, and not because the elevated 3-m whip has a better "line-of-sight" path to receivers.
//
Both should be legal
# 1 Mount the Part 15 AM transmitter on top of a tall building with a all metal roof, the ground wire and the antenna is under 3 meters. Signal should get out very well, much better than mounted at ground level. Say the ground lead to the all metal roof is 6 inches, and the antenna with loading coil is 111 inches since the total is 117 inches (3 meters = 118.110236 inches) then the installation should be legal.
# 2 Build a tall mound of dirt 50 feet (say you have enough land and have access to construction equipment). Mount the Part 15 AM transmitter on top of the mound. Build a ground plane spreading out from the base of the antenna and down the side of the mound. Connect 6 inch ground lead to ground plane and have a 111 inch antenna and coil. This should be legal and the signal should get out very well.
Maybe having the ground plane coming down the side of the mound might not be legal, if its a part of the "hill" ...then one must determine where a ground plane ends and a vertical ground plane begins. And does the ground plane coming down a natural hill would be more legal than someone constructing a 50 foot hill. Also the ground plane for this argument is 12 wires of 100 foot spread out from the base.
To further illustrate this, what about elevated groundplanes? If one built 12 wires of 100 foot each spread out from the Part 15 AM transmitter...but elevated 6 feet...since in theory it is a ground plane...how would this work preformance and legally.
If the argument is keep both ground and antenna under 118 inches...then if it is met...then everything else should be legal.
And lastly, what about using a metal fence four feet high and surrounding the yard as a ground plane?
(Some might argue if a mound of dirt 50 feet high is legal to put a transmitter on, it "should" be more legal than a 50 foot metal pole with a 6 inch gound connecting the transmitter and the metal pole..and should be far more legal than a 50 foot wire coming down a metal pole.)
Rich, I'm curious - how is your Part 15 transmitter installed? Is it ground mounted or elevated? What type of ground does it use?
kyradio, here are some comments based on physics alone.
# 1 Mount the Part 15 AM transmitter on top of a tall building with a all metal roof, the ground wire and the antenna is under 3 meters. Signal should get out very well, much better than mounted at ground level. Say the ground lead to the all metal roof is 6 inches, and the antenna with loading coil is 111 inches since the total is 117 inches (3 meters = 118.110236 inches) then the installation should be legal.
The metal roof no doubt will be electrically connected to the steel frame of the building, and that frame will be connected to earth ground. Reality is that the path through the building steel to the earth will constitute a radiating part of the antenna system, similar to installing the tx+whip on anything else at the same height as the building, and running a long conductor from the tx chassis to a buried r-f ground in the earth. So yes, the signal will get out relatively well, because the radiating lengths of the conductors attached to the tx will greatly exceed 3 meters.
# 2 Build a tall mound of dirt 50 feet (say you have enough land and have access to construction equipment). Mount the Part 15 AM transmitter on top of the mound. Build a ground plane spreading out from the base of the antenna and down the side of the mound. Connect 6 inch ground lead to ground plane and have a 111 inch antenna and coil. This should be legal and the signal should get out very well.
If the ground plane wires are buried and the base of the 3-m whip is ~ at the same height as the top of the mound, then the performance of this setup would be about the same as when installing the same configuration on flat land (other things equal). The propagation mode useful for Part 15 AM is the ground wave, which in this situation will have ~ the same field strength at a given distance as if the system was mounted on flat ground.
To further illustrate this, what about elevated groundplanes? If one built 12 wires of 100 foot each spread out from the Part 15 AM transmitter...but elevated 6 feet...since in theory it is a ground plane...how would this work preformance and legally.
If the elevated ground plane wires all lie in the horizontal plane, then the radiating length of the antenna system would be that of the whip plus the short lead connecting the tx chassis to the center of the ground plane. If the whip plus ground lead total is 3 meters or less then technically it meets 15.219. However I have read some documentation allegedly from the FCC that takes exception to this.
And lastly, what about using a metal fence four feet high and surrounding the yard as a ground plane?
The four foot height would become an effective part of the antenna system, so the total of the "ground lead" and whip connected above it would need to be reduced so as not to exceed the 3-m limit (if meeting 15.219 is the goal).
(Some might argue if a mound of dirt 50 feet high is legal to put a transmitter on, it "should" be more legal than a 50 foot metal pole with a 6 inch gound connecting the transmitter and the metal pole..and should be far more legal than a 50 foot wire coming down a metal pole.)
And they'd be correct. But the systems on the pole would outperform the one on the hill, because the radiating lengths of those pole-mounted antenna systems exceed 3 meters.
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Mojoe wrote:
Rich, I'm curious - how is your Part 15 transmitter installed? Is it ground mounted or elevated? What type of ground does it use?
Currently I am using only a Part 15 FM system. I don't attempt or want to be a "community broadcaster," only to transmit audio feeds from Internet websites from my laptop to my good stereo system in the next room. I can't tune in that signal on a good receiver for more than 100 feet.
My interest in AM systems goes back to my early career when I was chief engineer of licensed AM/FM stations, and even earlier to the times as a licensed "ham" that I built and operated amateur radio transmitters and antennas (high school).
Later in my career I was responsible for the technical analysis of various r-f systems in the commercial broadcast field, and thought that comments based on that experience might be useful to others on the Internet.
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Hello All,
I have been visiting this site for a good while now as I started setting up a part 15 station. My plans are to start the station for our church. We are in a small town so the 1 or 2 mile range would almost cover the town. I have spent a good bit of my own money to get the needed items to get us going. Now I wonder if what I am planning would be legal. I have everything I need except the transmitter. I have contacted the company a few months ago about the am1000 because it is FCC certified I thought I would be fine. I was going to mount it on the suggested 25 ft mast using the 102 in whip antenna and #10 copper wire to run down to a 8 ft copper ground rod. All of which I have already purchased.
So I guess my question is do I proceed with it and take my chances with the FCC or go a different way. Accorging to the setup guide for the am1000 I would be good. But after reading the posts here am not so sure now. You all have a great deal more knowledge than I have on radio tech. I worked for a while as a DJ on a small AM station but never got into the tech part of it. The station owner was also the engineer. What would you suggest I do?
Thanks in advance for any help you can provide.
RD
RD,
You should carefully compare the information in this thread with the information on the Rangemaster site regarding legal issues and draw your own conclusions.
One statement on the Rangemaster site is noteworthy:
Quoting: "We have found with customers that [sic] install elevated grounds or ground wires that are obviously intended to radiate most of the time an FCC agent will ask that they be removed."
I know of no connection from an elevated transmitter to earth ground which will not radiate so I have no idea how to distinguish between one "intended to radiate" and one which is not.
Consider mounting the transmitter at ground level grounded to buried radials. Ask yourself how this would be viewed with regard to the antenna/ground lead statement in the rules compared to an elevated installation.
You may choose to take your chances with an elevated installation and that is up to you.
Neil
Sorry, Sir. I don't know how I missed your comment of yesterday, concluding with this:
If a transmitter is installed on top of a metal pole (say 10 or 20 ft) and grounded to the top of the pole and the bottom of the pole is placed in earth ground or connected to earth ground through a thick cable that was not visible, do you think this would be acceptable?
_________
I presume you are asking whether or not this would be acceptable to a government inspector, irrespective of the physics involved.
IMO it may or may not pass such inspection, depending on the educational background, "marching orders," and disposition of that inspector.
But physics shows that an elevated Part 15 AM tx+3-m radiator with a visible or invisible radiating ground conductor in fact does not meet Part 15.219.
So anyone installing such a "Part 15" AM antenna system is subject to some risk, should they ever be inspected by the FCC, or other agencies with the same regulations.
//
Great comentary, great discussion, positive, encoraging and factual.
Carry on!
Pink really is my color, isn't it?
Experimental broadcasting for a better tomorrow!
"IMO it may or may not pass such inspection, depending on the educational background, "marching orders," and disposition of that inspector."
Your phrase above sums it up perfectly. This is why installations on top of metal billboards have been allowed and churches with long ground wires have not. So we take our chances and don't worry about it. If we are inspected and the agent has an issue, then we just politely correct it.
The one fly in the ointment from a commercial point of view is that if a customer is advised he can install up high with a ground, then there might be repercussions if someone complains and the installation has to be modified resulting in reduced range and the transmitter not being able to do what was promised.
Gerry
"krimles" posted: So we take our chances and don't worry about it. If we are inspected and the agent has an issue, then we just politely correct it.
If given the choice, then maybe. But the citation/fine applied to this "church case" did not (apparently) give that operator such a choice.
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Rich's comment makes me think that there is more to this particular case than we know. Isn't it very unusual for the FCC to immediately issue a fine, without first informing the offender about an infraction and then allowing them to correct it? In this case, the correction would have been simply to turn off the transmitter until the installation could be made compliant. I know that the FCC is more swift with its justice in the case of pirate operations, but this installation was obviously not a pirate.