I have did a lot of reading on the rangemaster site in the last few days. I found this on the site talking about grounding.
"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."
If I put in this filter I would think if inspected by the FCC that it would prove to them that the ground was only intended for lighting protection and not to any way enhance the transmitter radiation. From what I have read about FCC inspections a lot of it has to do with your intent to bend or break the rules.
RD
I wonder what attenuation an agent might consider enough? 100, 1000 or more ohms.
What size would the RF filter be? Here are some calculations...
Z = 2 pi f L
if f = 1.5MHz:
then for Z = 100 ohms, L would be approx. 10uH
then for Z = 1000 ohms, L would be approx. 100uH
It would be interesting to check range with and without this filter to see how effective it is.
Gerry
In this Information Age, it can be difficult to know the difference between opinion and fact. Opinion is, in my mind, a statement not supported by absolute or mathematical fact. Fact, conversely, is supported by real world demonstration or mathematic function or both; not some pseudo-scientific manipulation of either.
Much of the information available from kit manufacturers is written to satisfy the needs of the potential builder. And in most cases, only addresses the issue of FCC rule compliance as a subject the user might want to pursue at some point in time. Much of what is expressed in instruction manuals and web site forums and blogs are opinions. Of course, these literary aids are sprinkled with actual facts to give them credibility.
I have read forum offerings upon blogs upon articles over the past couple of years with very little real world or field testing backed by mathematical modeling to support the factual test results. I have found myself falling prey to some of the arguments including some of the radio voodoo passed on as operational (facts) traditions by other radio services (broadcast, WiFi, ham radio, CB). And then the real challenge: present the findings to the users of such technologies so that the least experienced user can understand the outcomes.
And finally, without a historical perspective of how we got to where we are currently, in the FCC regulatory jungle, we remain lost in the moot discussion about what the current rules really mean. If field strength was really the finite determination of Part 15 rule compliance; the length of the ground lead was the real measure of compliance or whether there should be a high impedance RF choke in the ground lead, then why aren't there more stories of regulatory enforcement involving these kind of violations or suggestions for full compliance from regulatory agencies.
One such incident does not support the entirety of any single contention without all of the facts and the actual log of processes and practices involved in prosecuting the law by the commission. Most of which I have yet to read here in this, or any other, forum thread. I have been a consultant to the FCC for over 20 years and also operate a Part 15 community radio station. I strongly suggest strongly that you don't even believe what you read here. Find out for yourself. Read the FCC enforcement log. The FCC considers it your responsibility if you operate a transmitter in any of the terrestrial or spacial/orbital radio services. I encourage you to find the truth.
Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.
Rhema Radio - The Word In Worship
Las Vegas, Nevada, USA
http://www.rhemaradio.org
Neil said:
The "gray area" mentioned in a link in the EH thread to a manufacturer includes a statement of the possibility that the legality of an installation may be a matter of interpretation by a particular FCC inspector. This is not good guidance since the rules are clear about ground, etc. lengths and to give plans for installations which illustrate long ground leads which exceed the 3 meter limit with the expectation that many FCC inspectors "approved this" is not a very reliable way to guide customers.
Neil, I would have to disagree on one point. The rules are not clear, which is exactly why there is so much debate, discussion, confusion, etc.
Yes, the rules state that the "ground lead" is included in the 3 meter length. I have yet to see any official explaination of what type of "ground" that we are supposed to connect our "ground lead" to. In fact, I posed this question here a while back. Is the electrical ground in my house "ground"? Is a water pipe "ground"? Is a steel roof "ground"? Is a "ground plane" "ground"?.
You see the ambiguity about this point of the rules, I presume? I understand your contention that a "ground" is direct earth ground, but given that the FCC has not made that distinction in the rules, and given that the definition of a "ground" in many other technical professions does not limit itself to only an earth ground, you can see why this is open to some interpretation.
Even if we assume that an earth ground is what was meant, does that mean a single ground rod, multiple ground rods, or even a series of ground radials? Again, the FCC does not specify in Part 15 rules. Even if what constitutes a "ground" is specified in other FCC rules (broadcast rules, for example), those rules were written for a different set of conditions (especially power) and we can't say for certain that the FCC intended to apply those exact same conditions on Part 15. If they did, then we'd all be required to have 120, 1/4-wave buried radials under our little 100mW transmitter.
I'm not trying to dispute your point of view. I am simply pointing out that there is some room for interpretation in the Part 15 rules (specifically 15.219). I might also speculate that if the exact nature of what constitutes a "ground" was of importance to the FCC in this instance, they would have defined it more clearly in Part 15. Perhaps they knew what they were doing when they wrote section 15.219 and left some flexibility there, on purpose.
I do agree that extremely long ground wires are probably asking for trouble, as evidenced by the church that was cited. However, if someone uses a nearby water pipe as a ground, I think that is more reasonable and would probaly pass FCC inspection. However, as other postings have indicated, anything is open to the interpretation of the individual inspector.
I think it all boils down to this - if you are not "pushing the envelope" with your installation and you are not causing interferance, the likelyhood of getting a visit from Uncle Charlie is small. In other words, I think we make too much of this issue. But that is just my opinion. You have your opinion and so does everyone else here. On this particular topic, none of us know the true facts, since they are not spelled out by the FCC.
Gerry said: Z = 2 pi f L
I'm being nit-picky, but that is the formula for inductive reactance. For impedance, you have to take into account the resistance of the coil. However, in this case, the resistance is so small that we can say "close enough".
Marshall,
Once again you have posted an excellent commentary and I really appreciate your thought provoking approach to the subject. I hope what I have to say in response adds to what you have said.
You mentioned knowing the history of how we got here. We do. Around 1937 the FCC rules were extended to allow for "phono oscillators" for the purpose of allowing the production of phonographs which could work with existing and expensive radios (about 1 week's pay from what I have read) without requiring duplication of the audio amplifiers and speakers. Due to the difficulty in measuring field strength as specified in 15.209, part 15.211 was established as prefaced in 15.211 in the '50s by the phrase "in lieu of field strength limits in 15.209...". In subsequent revisions, this became 15.219 and the phrase "in lieu of " was dropped, though it appears that this makes no difference since we can choose 209 or 219. One point to infer is that the original intent was not for anything other than personal use of these devices in one's own home; that is to say community broadcasting was not and is not the intent of part 15 rules.
Through clever advances in technology we now have the means to achieve ranges which were never intended in the original rules. Our advantage is that the rules have not been revised to further limit the AM range so it would only work in one's home.
You also discussed that we should obtain information. I agree, yet my attempts to put aside opinion and gather real facts have not bourn fruit. Recently, on another board, I asked the operator of a part 15 AM station which "passed FCC inspection" to share the details of his installation. One poster said it was not proper to badger him since his station was "approved" and that he did not need to justify anything to me. All I sought was information about a station which is "legal" so we may get some guidance yet there is no information forthcoming. We have the situation of the citation of a church, yet we really do not know the facts in enough detail to understand what really happened. I have seen statements alleging that many "elevated" transmitters were inspected and cleared by the FCC yet there is no data of which I am aware, anecdotal or otherwise, which enumerates those who were and those who were not. We are left to speculate that it is "up to the FCC inspector" and the installations detailed on the Rangemaster site "may be a gray area".
It may well be that if one reads the actions on the FCC site one gets the impression that few AM part 15 operations are cited and that may indeed be the case. It may also be true that we need not worry about enforcement against ground leads which are 20 feet long. This thread is full of opinion and I really wish we could start getting some facts. Lacking this I tend to take the literal mathematically and physically supported position that the rules address the ground lead length to be from the transmitter to the dirt.
Neil
Mojoe,
In technology and engineering there is an expression which goes "known to those practiced in the art" which means that technical terms are understood in technology without the need for definition everytime they are used. For example, if you measure the voltage at an outlet and tell me it is 120 volts it is not necessary to explain to me the meaning of volts. It is also not necessary to explain to those "practiced in the art" the details of measuring the final stage input power in a transmitter to assure it is 100 mw. or less.
The same is true for those "practiced in the art" of radio technology. The length of a ground lead is measured from the device to where it literally enters the earth. That is why it is called a ground. It is my opinion that the FCC is using this terminology in a standard and accepted manner and in your example of a water pipe "ground" at RF it would have to include the length of the pipe to the point where it goes into the ground. The same is true for the ground connection on an outlet. It is not grounded at the outlet, it is grounded at the stake at the service drop.
Neil
Neil,
Although I have no experience in broadcast radio (although I do have friends in broadcast radio), I have been involved in the electronics and computer fields all my life. I have also been a ham for over 20 years. Having said this, I would have to disagree with you on a ground having to always be physical dirt. I don't want to start a semantic argument about this, so let us just agree to disagree on this, ok?
You mentioned having some discussions on "another" forum. It so happens that I was recently reading some of the discussions on various topics at that forum. I note two distinct differences between that forum and this one. First, this forum provides much more useful information and far less debate. Second, that other forum tends to be somewhat hostile, with some members resorting to name calling. Thankfully, things are more civilized here.
Does anyone have one of the ground lead filters sold by Hamilton? What is the rated inductance?
Any opinions on Gerry's suggested impedance values? I would think that 1K Ohms should be sufficient. What do others think?
I may take my LCR meter and dig through my box of inductors. If I have something suitable, I may do a test on my transmitter installation. Otherwise, I'll see if I feel like winding something.
If a "good earth" impedance is 20 ohms, then I would think that adding an RF impedance of 1000 ohms at the transmitter would be a good value to try.
Gerry
Here is a good definition of ground as applied to antennas (paraphrased from a website):
An electrical connection to earth as a reference potential for radio frequency antenna signals. As high frequency signals can flow to earth through capacitance, capacitance to ground is an important factor in effectiveness of signal grounds. Because of this a complex system of buried rods and wires can be effective. An ideal signal ground maintains zero voltage regardless of how much electrical current flows into ground or out of ground.
The last sentence in the paragraph above is very important, especially as concerns the use of "massive wires" considered by some (even Part 15 tx OEMs) as providing a "ground" to an elevated transmitter installation (on a roof top, flag pole, mast etc). The ONLY part of such a ground wire approximating the true electrical characteristics of the earth at radio frequencies is the part that is IN the earth. Once that conductor exits the earth, it behaves as an antenna for radio frequencies. The top of such a "massive wire" has greatly different r-f properties than the part that is in the earth, and in fact, that ground wire often contributes the largest part of the total radiation from such an elevated Part 15 AM system.
To illustrate the point, there is a type of monopole radiator used in commercial AM broadcast consisting of an uninsulated tower directly connected to the earth at its base via ~120 buried radials. It is driven by applying tx power to it at some physical height above the earth. This is possible, because the impedance of the tower at radio frequencies is a function of height along the tower face. This tower has essentially zero impedance when measured on the structure where it enters the earth, but when properly driven still functions as a very efficient radiator. This application and the elevated Part 15 tx+whip used with a long conducting path to something buried in the earth are electrically identical.
In some applications it is impractical to use the earth as the reference potential for a vertical monopole antenna. In such cases a properly designed network of horizontal, non-radiating, elevated conductors can be used as that reference, but the better term for such would be a counterpoise, rather than "ground." And their use for Part 15 AM systems might take some convincing for FCC inspectors.
Lastly on this subject of radiating ground wires, the Rangemaster website allegedly states that running such a ground wire up to the elevated tx via a metal conduit that is connected to the earth only at the bottom will inhibit radiation from the ground wire. But just as with the bare ground wire itself, that conduit would have the electrical properties of the earth only for the part of it that is physically buried in the earth. And like the ground wire, that conduit will behave as an antenna once it exits the earth -- so there is no real benefit in using it. This was confirmed rather easily using NEC.
//
Quote:
"The range achieved with the original installation apparently was satisfactory with the long ground lead, yet was not adequate when the transmitter was installed at ground level."
So what was the range?
WDCX AM1610 Part 15
John
Owner-Operator-Chief Engineer-Program Manager
Mojoe,
Though I don't think you took my comments personally I want to mention that I was not questioning your being "practiced in the art" and from what you posted above and from reading your other posts I would say you know electronics and radio well and that you understood my argument regarding commonly used terms. We probably could go back and forth on this topic but we both have presented our take on it so I accept that we disagree. With that said, I am not closing our debate and if you want more discussion I am open to that.
By the way, I noted that your writeup on the colinear coil/antenna is on the SSTRAN site. Nice!
Neil
According to the Talking House site, their transmitter is "100% FCC Approved", 3 meter antenna.. and it's grounding would be the wiring of the house where it's plugged into an outlet. The "external transmitter" ATU may ground in actual dirt, not sure on that, but it's an option not "stock".
So while one can do a lot of debate over the technical definition of a ground, it at least seems that something other than actual physical entry into dirt has been deemed "approvable" with at least that unit.
Daniel
Did you notice if Talking House states that the unit is FCC Part 15 certified for use with the ATU? I recently obtained the ATU on Ebay as this would be a great setup having the transmitter in the house, ATU/antenna outside. The individual that sold it said the ATU is available from Talking House and is certified for use with either 75' or 125' of coax between the transmitter and ATU.
I posted the same question in another thread but no info has been offered yet.