If you look closely, it appears there is a ferrite choke on the ground lead.
I looked at the picture carefully, but I was not able to see any sign of the choke.
The particular ferrite core specified in the Rangemaster website has low permeability and Q at the upper end of the AM BCB. Its effect is to increase the resistance of the ground lead and thus reduce the efficiency of the transmitter.
A perfect RF choke in the ground lead, on the other hand, would not allow the transmitter to work at all if there are no other RF paths to ground (such as through audio and power cables). A perfect RF choke would stop any RF current from going into the ground lead. This would be the same (RF-wise) as disconnecting the ground lead of the elevated transmitter.
So what you do is build a tall giant drain-pipe right alongside the radio tower filled with dirt, bringing the ground up to the top of the tower. Of course a super-thick copper wire would run all the way down within this pipe-of-dirt, but it would be officially "in-the-ground." Has anybody ever done that?
Ya know, it probably wouldn't matter if you were 100% legal and compliant in every respect. If they say you are causing interference, it doesn't matter. They can shut you down.
I doubt that this station was interfering with anybody. And if it were, the problem could easily have been resolved by moving to a different frequency.
The FCC rules governing unlicensed operation in the AM band were written many years ago when the band was a lot quieter. The requirements concerning grounding in Section 15.219 are unnecessarily burdensome, arbitrary, and subject to a great deal of interpretation (as we all know). It is time to change them.
I have a plan for doing this and I am starting to gather support for it. If you are genuinely interested in community broadcasting and have expertise in the areas of engineering, FCC policies and procedures, media and publicity, or actually own and operate a community radio station, I invite you to contact me through the member e-mail system.
Together, we can work to change the rules for the public good. There has never been a better time than the present!
Grounding is not the issue here. It is instead too much signal in the air for the FCC inspector. Let's stop a minute and look at the reality of this situation. This FCC inspector "will only make an inspection" if his office in Vancouver, Wa. receives a written complaint. I have worked with this particular inspector personally. He has explained to me first hand, he does not start an inspection process without the written complaint. He covers too many radio-type services over too large an area to instigate the process on his own.
Stayton, Oregon has a local AM BCB commercial radio station and would be the first person I would look at for the complaint. Also, being 20 miles from Salem and about 25 miles from Albany, both of these towns have over 15 local radio signals that are listened to by people in the Stayton/Aumsville area. Let me say this very slowly; MAKE FRIENDS WITH LOCAL COMMERCIAL BROADCASTERS. Even small local AM radio stations have hundreds of thousands of dollars wrapped up in their operations. If you were them you would be protective too. Take the lead and take the high ground here. Ask their engineer to help you with your technical questions.
On another note, WEAK-AM has a very good point. The FCC grounding rules for Part 15 are ambiguous and vague. And have the FCC consider cleaning up the rules would be helpful in operating in compliance. I applaud your efforts.
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This could easily be a new forum thread, but it also follows the grounding subject on this thread, so here we are.
I once described how I use a six-foot foot aluminum window frame as an indoor/outdoor antenna, as follows: The SS Tran is on the floor below the window with a 2.5-ft. wire straight up and screwed to the inside bottom of the metal window frame. Outside on the porch another 2.5 ft. of wire is screwed at the top of the window frame and run up the wall underneath the overhanging roof. This arrangement gives good indoor/outdoor coverage, but there's no ground.
Right under the floor is the home's 100-ft long steel I-Beam. What if that were attached as a ground plane? It's more or less at ground level and it's under the floor as if "underground."
Would that I-Beam radiate from the side like a horizontal wire antenna, or out the ends?
The biggest obstacle to simply testing it is finding a way of attaching a good electrical connection to such hard metal. Ideas?
In the first post of this thread, I said that the radiated power that corresponds to a field strength of 4 mV/m at 137 m is 3.34 mW. I did not post my calculations. However, on another website, there is a thread in which the topic of this thread is being discussed, and someone calculated a radiated power of 8.3 mW. I will explain here why I think that 3.34 mW is the corrext value.
It is well-known that an electrically-short vertical antenna over ground produces a field strength of 300 mV/m over a perfect, flat, ground at a distance of 1 km when the radiated power is 1 kW. The antenna in question has a total length of about 15 meters when including the 40 foot tower and the whip antenna. The wavelength at 1620 kHz is about 185 m. The electrical length is about .08 wavelengths, which is small. 137 m from the antenna is a short enough distance that ground attenuation is not a factor in determining field strength.
Field strength varies as the inverse of distance and the square root of power. (137/1000)(4) gives a field strength of 0.548 mV/m at 1 km for the system in the NOUO. The radiated power is [(0.548/300)^2] x 1000 = 0.00334 W = 3.34 mW.
May I ask what kind of range you are getting with your current arrangement?
Looks kind of like a combination electric and magnetic thing. IOW, a window frame could be a magnetic loop.
Does the window frame have metal mullions? If so, could they be forming fractal elements? If not, what would happen if you introduced a square or round wire just inside the point where the inside wire attaches to the center of the bottom window frame ... IOW, would it couple it?
Dunno if it's big enough to meet your needs ...it's for a trailer:
http://www.yourbroadbandstore.com/product.php?pid=703233
HTH ...
After some research, I discovered this operator has multiple Hamilton Rangemaster transmitters (3) within the same town. The town is about 2.5 miles across. The transmitters are GPS synchronized. So, at a particular point all of the signals would potentially be additive. It is possible for the excessive field strength to be the product of several signals "beating" together.
In other words, grounding may have little or nothing to do with this matter. In my years of radio and dealings with FCC inspectors I have had this situation arise several times. Most notably an accusation of over modulation on FM. It was later discovered to be the product of multi path.
This particular operator is operating FCC certified Part 15 transmitters. And to get the transmitters to synch together would require a well done installation. The pictures of the station gives one the impression these folks take what they do seriously.
For more information on GPS synchronized transmitters drop Keith Hamilton a note or visit the Rangemaster web site.
We don't have information about where the multiple transmitters are located with respect to each other, or if they are, indeed, synchronized. However, assuming that they work together as a directive array, two transmitters can give a maximum field strength increase of 6 dB, and three can give a maximum field strength increase of 9.54 dB.
A really good ground-level mounted Part 15 AM installation might produce a radiated power of 0.1 mW. This low radiated power is because of the very low radiation resistance of a 3 m MW antenna that is not elevated. The field strength measurement in the NOUO indicates a radiated power of 3.34 mW, which is a bit more than 15 dB over a ground-level installation. Because the numbers used in this post are rough guesses, 9.54 dB is comparable to 15 dB. So, the hypothesis of constructive interference of the wavefronts of multiple transmitters is not ruled out; but I think that the much higher radiation resistance of the elevated antenna is a more likely explanation.
"So, the hypothesis of constructive interference of the wavefronts of multiple transmitters is not ruled out; but I think that the much higher radiation resistance of the elevated antenna is a more likely explanation"
Well, if you could include some combination of both proposed reasons without cancellation, especially if the TX' in question are properly synced via GPS NIST, which are, for all practical purposes, perfect, then would we have a viable explanation?
simple fact of the matter if a local licensed station wants you off you are off.
does not matter how much you dot your i's and cross your t's or even whether or not there is interference.
you are off simply because a legal licensed station wants you gone and unless you have tons of $$$ and a van load of lawyers you are not going to win.