Source: https://part15.org/forums/topic/knife-edge-limits-for-%C2%A7-15-221-operation-in-the-band-525-1705-khz/
Timestamp: 2019-04-21 06:37:19+00:00

Document:
Knife edge limits for § 15.221 Operation in the band 525-1705 kHz.
Home › Forums › Regulations / Law › Knife edge limits for § 15.221 Operation in the band 525-1705 kHz.
Before I ask to spend non-grant money on hiring a professional RF engineer to do the measurements, I wanted to make sure I understand the regulatory.
§ 15.221 (2) states: At the perimeter of the campus, the field strength of any emissions, including those within the frequency band 525-1705 kHz, shall not exceed the general radiated emission in § 15.209.
Our campus is irregular in shape, crosses streets and involves a river. How would you calculate the perimeter?
When drafting 15.221 we think the FCC had in mind a perfectly round campus.
This will be an interesting thread to watch if anyone is bold enough to venture an answer.
If your campus has any across-the-street parking, an annex, a steam/power plant or admin building a bit of a distance away from the main grounds, that may help a bit in “rounding off the corners”.
Otherwise, for a question like this, it might be worth your while to sign on with one of Barry Mishkind’s pro broadcast forums (found at radiolists.net) and throw the question out to the crowd there. In all likelihood someone there has already done it, so you need not have to reinvent the wheel.
Not exactly what I was looking for as it basically cuts away 2/3 of the campus.
An unlicensed AM transmit system exactly meeting FCC §15.219 most likely would permit much higher field intensities at the campus perimeter than using §15.209.
NOTE regarding my post above: Some of the assumed 85mW of output power is dissipated in the radial ground system. Those effects are included in the mileages shown for various Earth conductivities, in the table.
How are your own engineering chops? Can you park the transmitter/antenna close to one end of the campus and put a passive antenna some distance behind it? You are essentially creating a short-form directional array to beam the signal straight down the heart of the campus.
Yes, BillyBurg, I would maintain that the antenna arrangement you described would be FCC legal by the simple fact that it is not disallowed anywhere in the Rules.
RF measurements at the property line are the single test of compliance.
I personally believe it reasonable that a 15.221 system to reach all areas of the campus even it results that certain directions go a little beyond “borders” of that irregular shaped campus.. Now obviously my opinion doesn’t mean squat, but again, if you consider it from another angle; it is unreasonable that an educational system should have to eliminate a substantial part of it’s campus reception just because of it shape..
What’s more, most educational campus are probably not round and it’s highly unlikely for it to be common practice that such stations only serve a portion of their campuses. It’s much more likely, in fact probable that most of them do and have always provided a listenable signal a reasonable distance beyond the confines of the campus.
If I were you I would contact Bill Baker of ISS who is the leading supplier of these type of systems and ask his advice. I assume you’ll be buying from him, but even if not, he would willing to provide you some insight about your concerns.(he’s a nice guy).
Bill Baker already quoted on a TR6000 Model 15.73 and ANXX Antenna to operate under § 15.221.
Waiting to see if of the grant materializes.

References: § 15
 § 15

§ 15
 § 15
 §15
 §15
 § 15