Signal Strength/Distance Question for Part 15 AM

[Hamilton]

To the letter of the law, any wire that radiates that extends beyond the 3 meters is in violation if it isn’t filtered or shielded.

The transmitters I have looked at have the radio ground tied straight through to the house wire, a direct connection, no power transformer or such, a direct wire from the radio ground to the electrical socket.

My point here is that I think the hoopla about the 3 meter radiator is to be kept in perspective with a million inside tabletop AM transmitters radiating into house wiring.

And like I have said and I think you are saying Tom, there are intentional and non-intentional radiators, the house wiring probably would not make a great radiator, it was not designed, intended to be a radiator.

 

[Hamilton]

I think it is apparent that an electrical wire system is a poor radiating system since carrier current transmitters (which are designed to radiate through the building wiring system) send 20-30 Watts of power into the house electrical system just to achieve Part 15.209 level field strengths.

This is 200-300 times the power of a Part 15.

Also generally just one ground rod is not a great RF ground, but adequate for lighting protection.

I think really with all the discussion that has been going on this is the way I see it, or would work with any ground rules:

If a ground doesn’t look like it will be a effective radiator, I wouldn’t be concerned.

If I am working with a system that is using a ground where I am concerned the ground may radiate (drainpipe, bill board) I would use some method to filter or shield radiation after the ground lead.

I think it comes down to (is the ground intended to radiate? Or is it an effective radiator?) If it is then some method should be used to limit the radiator to the 3 meter limit.

Obviously grounds that are intended to radiate are clearly addressed by FCC policy.

Here is the note Rich got from John Reed:

“As to the ground lead, this is exactly what we've been saying all along. If you attach your ground lead to a drainpipe, billboard, or other structure, that structure becomes part of the ground lead and is included in the 3 m limit. Similarly, if you install a ground plane or otherwise change the ground efficiency”

Contrast that with official FCC policy:

The 3-meter combined length specified in Section 15.219(b) refers to the length of all radiating elements. Attaching the ground lead to an unshielded radiating object, or the addition of a ground screen, will cause the effective length of radiating elements to exceed 3 meters, in violation of Section 15.219(b).
Both are basically saying the same thing, if it radiates, it is included.

So I see no reason to filter or otherwise shield a ground that is already a poor radiator.

What does everyone think?

 

[audioguy]

I am not trying to throw fuel on the fire, but some of you in the Chicago area will recall that a few years ago, Old Navy operated a Low Power AM station from a billboard adjacent to the Kennedy Expressway in Chicago. I do not know the manufacturer of the transmitter, but it was mounted on the billboard, high in the air. The signal was audible for several miles.

Although the installation was inspected by the FCC, it was not shut down. To my knowledge it continued to operate for quite some time until another client took over the billboard.

 

[rfry]

If a ground doesn’t look like it will be a effective radiator, I wouldn’t be concerned. ... I think it comes down to is the ground intended to radiate?

That may not concern the writer of the quote above, but would it concern an FCC inspector? The fact that a ground conductor doesn't "look like it will be an effective radiator" doesn't mean that it is not an effective radiator. Conductors can and will radiate whether or not the user intends them to do so.
//

 

[Tom Wells]

I am not trying to throw fuel on the fire, but some of you in the Chicago area will recall that a few years ago, Old Navy operated a Low Power AM station from a billboard adjacent to the Kennedy Expressway in Chicago. I do not know the manufacturer of the transmitter, but it was mounted on the billboard, high in the air. The signal was audible for several miles.

Although the installation was inspected by the FCC, it was not shut down. To my knowledge it continued to operate for quite some time until another client took over the billboard.

I used to use AM 1550 until the talking billboard "happened". It was Radio Cadlliac before Old Navy, I think.
It certainly did cover 2 miles, I always assumed it must be 5 watts. I'd love to have the reach they did, but
the audio was some kind of awful. Sounded like a bad answering machine in the cassette tape days.

 

[audioguy]

Yes, it was on 1550! And the audio sure was bad! I'm thinking that was due to the source, not the transmitter. I think this all happened about the time that the LPB AM-2000 came out, and there must have been an article or two about it in Radio World. So maybe that was the transmitter they used. Anyway, I think the audio must have come from a cassette machine. I don't think good sounding digital audio was available back then. That was well before iPods.

 

[radioman148]

I used to hear that "Old Navy" station as well when driving down the Kennedy. As I remember it their coverage was better than 2 miles. I could hear them from the junction to downtown and if I remember correctly their billboard was around Fullerton I think.

 

[Hamilton]

In the old days it was purely up to the agents digression, whether to allow any ground. (I talk with them) I suspect when this installation was inspected the agent read the rule, and moved on to more important things he had to do.

I have seen agents do many things, I have had them call me and say they have never heard of part 15, they stumbled on one, expecting a pirate.

It probably wouldn’t pass today given the latest policy statement recently broadcast to all agents.

The LPB AM2000 was basically the transam transmitter. LPB discontinued it ($1895 price tag). Of course LPB doesn’t answer it phones at all these days I hear.

Oh and Rich, What I mean is if the tech/engineer on site has determined that he thinks that his ground isn’t effectively radiating, then I don’t think the FCC would question it. Or if it is a configuration that is approved by an engineer, I didn’t mean just if some non-tech person looked at it and guessed it might not radiate effectively.

I was thinking of taking information about radiating grounds off the page, even though I try to inform that they will not be approved should an agent visit, I guess strictly speaking the information shouldn’t be there.

What do you guys thing, radiating ground how to information:
Informative or improper?

See http://www.am1000rangemaster.com/pdf/hints.pdf

 

[Hamilton]

One other thought, Ray Laforge (FCC) told me once basically what I said in the previous post,
that if an tech/engineer had determined that a ground was not an effective radiator, then an agent generally would allow it unless the determination seemed outlandish.

 

[Neil E.]

....
Oh and Rich, What I mean is if the tech/engineer on site has determined that he thinks that his ground isn’t effectively radiating, then I don’t think the FCC would question it. Or if it is a configuration that is approved by an engineer, I didn’t mean just if some non-tech person looked at it and guessed it might not radiate effectively.
...

Well, if this is the case then I am sitting pretty. I have two electrical engineering degrees, am a Registered Professional Engineer in Ohio, and have an Extra Class Amateur Radio License. Does this really mean that I can defend my installation simply based on credentials? I admit to a bit of sarcasm here but do you really think that my opinion would be a factor in the event of an inspection which did not meet the inspector's muster?

Neil

 

[Timewarp]

Wouldn't it be a shame or a big laugh to see one busted as the most podunk pirate in radio history!!!!!!!!!

FCC agent "Hey! You've got 2/100ths of a watt ERP. That's double the part 15 limit. What's a
grown man with your experience doing this for anyway."

 

[Neil E.]

Wouldn't it be a shame or a big laugh to see one busted as the most podunk pirate in radio history!!!!!!!!!

FCC agent "Hey! You've got 2/100ths of a watt ERP. That's double the part 15 limit. What's a
grown man with your experience doing this for anyway."

Yep. That's the situation as I see it regarding credentials as a valid excuse to bend rules. It's called hubris.

Neil

 

[rfry]

FCC agent "Hey! You've got 2/100ths of a watt ERP. That's double the part 15 limit.

Details at first may not be important to some, but ignoring or misunderstanding them still may result in FCC action.

Note that a Part 15 AM transmitter / antenna system that is compliant under either 15.209 or 15.219 in the upper part of the AM broadcast band can produce an ERP not greater than ~50 nanowatts (0.000 000 050 watts).

The "2/100ths of a watt ERP" stated in the quote above is ~400,000 times greater than the maximum legal ERP to meet 15.209 or 15.219, which is far from "double" that ERP value.

Even 1/1000 of a watt of ERP is still excessive for legal Part 15 AM ( ~20,000 times greater ERP than complies with the realities of 15.209 / 15.219).

//

 

[Neil E.]

The "2/100ths of a watt ERP" stated in the quote above is ~400,000 times greater than the maximum legal ERP to meet 15.209 or 15.219, which is far from "double" that ERP value.

Even 1/1000 of a watt of ERP is still excessive for legal Part 15 AM ( ~20,000 times greater ERP than complies with the realities of 15.209 / 15.219).

//

Once again Mr. Fry is correct. He He Heeeee.

Neil

 

[Timewarp]

Yes!!!!!!! But the joke is not on me because the FCC licensed transmitters that I am babysitting
right now put out thousands of watts. Mr Fry's expertise in this matter only made my point even
more clear.

Have fun with your toys big boys!

 

[Neil E.]

Timewarp,

I certainly was not trying to make anyone the butt of a joke. As I try to understand your last post I must ask what happens if your babysitting activities for the transmitters putting out thousands of watts allows them to exceed the authorized power or they have distorted patterns?

Could not the same happen to us using peanut whistles and toys?

Just asking, not joking.

Neil