FCC issues a rare "ground lead" NOUO

I feel bad for KENC (the station name)
seems like they were really working hard to serve the community.
I hope he doesnt shut down but instead uses a shielded cable.

Question regarding your post "I hope he doesnt shut down but instead uses a shielded cable".

How would that help and where is this addressed in 15.219?

I did find the following from the NOUO to be interesting

"however, the referenced antenna's ground lead was attached to an unshielded radiating metal tower in which the height of the tower measured at approximately 40 feet long (12.2 meters). This antenna installation violated Section 15.219(b) of the Rules. See 47
C.F.R. 15.219(b)".

Namely the reference to"unshielded metal tower". I would really like to know what a shielded metal tower is.

Neil

Ill chosen wording from an explanatory point of view, methinks 😉

The 'tower' is like a mast, but at 40' obviously required more structural soundness. I guess the inference is that the ground lead attached to the tower made it part of the radiating system ... and by the looks of the field strength measurement, more than 800 x the value allowed by the rules, it certainly was out of compliance,

So the guy was breaking both sections of Part 15, antenna/ground length, and field strength radiation ... not by a little, but by a huge amount.

I guess they mean that if a metal mast or tower has a ground lead attached, then it must be totally shielded, no radiation escaping, or else it will be considered an 'intentional radiator', part of a dipole antenna.

If the lead to RF ground is only open a few inches at the antenna base and not attached to metal mast (e.g., my mast is fiberglass), and the rest is shielded cable with, say, it's shield attached to the building's electrical ground, would that be enough, field strength not withstanding, to bring it into compliance?

In the FCC notice, the inspector notes that the tower is radiating. We could assume either a bare conductor runs down the tower or is connected to a grounded metal tower near the elevated transmitter. If an operator were to use shielded cable for a ground conductor, the cable shield would need the earth end connected directly to earth ground, not house wiring grounds to decouple the signal. One of the best ways to keep ground conductors from radiating is to run the ground conductor through a toroid core several times near the transmitter to choke off the current in the wire. And finally, 40 feet of almost any kind of metallic conductor at AM broadcast frequencies when hooked between the ground of the transmitter and earth ground will radiate. I know this inspector from the FCC. He knows his stuff. Plus I contract engineered the local commercial AM station several years ago. It is way out in the sticks. This operator had to tweak someone in town who then filed a formal complaint with the FCC to get inspected. 'Nuf said.

The field strength of the signal on frequency 1620 kHz was measured at 4000 microvolts per meter (uV/m ) at 137 meters, which exceeded the maximum permitted level of 14.8 uV/m (24,000/1620) at 30 meters

4000 uV/M @ 137 Meters instead of 14.8 uV/M @ 30 Meters?

That's seems like a whole lot more than a non-compliant ground lead on an otherwise compliant transmitter.

270 times the expected power measured at 4-1/2 times the distance?

One of the best ways to keep ground conductors from radiating is to run the ground conductor through a toroid core several times near the transmitter to choke off the current in the wire.

Great point, and a question that comes up from time ot time!

Section 15.219 of the Rules (100 mW to the final stage and 3 m antenna length) is an alternative to the field stength limits of Section 15.209. 15.219 was intended to allow hobbyists who do not have a legal calibrated FSM to comply with the rules. It is necessary to meet either 15.209 or 15.219, but not both. 15.219 has no field strength limits.

It turns out that the field strengths possible with a legal 15.219 installation are much higher than the 15.209 limits. I have pointed out in other posts that the 15.209 limits (also 15.221 and 15.223) are too low to be measured by an FSM in an urban environment.

I have been told that, back in the late 1930s, when the FCC wrote the rules that later became Part 15, reception of AM stations from other countries was routine. The AM BCB must have been a lot quieter back then. Since the limits have not changed much over the years, this may explain the impossibly low field strength limits of 15.209.

Who Ratted Him Out? I have my guesses, but then again, I am usually wrong.

I would presume above is the tower in question by the FCC. It is not 100% clear to me but it does look like the ground wire is attached to the tower.

http://www.kencradio.com/images.php
it also appears that his main and stadium xmitters are close to overhead lines which should help propagate the signal as I understand.

QUESTION: So if he simply runs an unshielded ground wire down the tower with 2-6 inch standoffs as shown in the drawing in the back of the AM1000 manual, shouldn't he then be in compliance?

Steve
1610am
Oregon

"QUESTION: So if he simply runs an unshielded ground wire down the tower with 2-6 inch standoffs as shown in the drawing in the back of the AM1000 manual, shouldn't he then be in compliance?"

No. Part 15.219 makes no exception for choked, insulated, blue, or shielded (whatever this is) ground wires.

Neil

Thanks to chilly1610 for finding the kencradio.com website. Ken C. sure has quite a station! He is obviously a pillar of his community. Maybe he can get his coverage back by using more transmitters. According to the website, the transmitter in the NOUO is a Rangemaster.

An illustration of the use of a long ground lead was in the AM1000 manual some time ago, but said illustration has been removed from the manual. The latest edition of the manual may be downloaded from the Rangemaster website.

Choking the current in a ground wire ought to create a great deal of ground resistance, no? I'm having trouble visualizing how that if it just prevents a dipolar situation, it would have any value other than a safety ground.

1) Why a toroid core instead of an RF choke?
NOTE: I have some RF chokes around, but a good toroid core cannot be found here.

2) If we kill the current to ground, but want the RF ground for radials, how would that work?

3) Regarding shielded cable, if the RF ground, which is not isolated from the TX component ground in my unit, is using the center wire, then what the heck is the cable shield connected to?

KENC Radio.

KENC certainly went through alot of expense to give this community a radio station they could be proud of.
And yeah i wish rock 957 had a studio like that. 🙂

I hate to see a station genuinely trying to serve the community fall, especially considering that there is no provision for LPAM Community Radio as there is for LPFM Community Radio ... perhaps the rule changes for LPFM will pass Congress, and more such stations can come into existence, but for Part 15, this one was clearly way out of compliance in several ways.

If it has a good listener base, I'd think he could garner enough support to create a sync'd constellation for coverage. I've been thinking a lot about that lately, and have come to the conclusion that, at least for my situation, it's a better solution over the long haul anyway. Using separate TX' and wireless routers, Barix Exstreamers, and highly directional mini-dish antennas as translators ... If one TX has a catastrophic failure, you'll only lose that portion of coverage, not all of it.