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College Radio 101: UW-Parkside Station Learns When You Need a License

The University of Wisconsin-Parkside’s student-run station WIPZ has apparently been on the air since the early 1990s, broadcasting on AM, then FM and online. The station has never had a license, presumably operating at very low power under what are known as Part 15 regulations which govern unlicensed operation of devices that radiate radio frequency power. These are the same regs that dictate the operation of the small transmitters sold to broadcast an MP3 player into a car radio.

Last week WIPZ learned a tough lesson from the FCC when agents showed up and determined their signal was broadcasting at a level way above the limits set by Part 15 for the FM dial. In fact, the agents reported measuring the signal at 334,559 microvolts per meter (uV/m) at 3 meters. Compare that to the Part 15 limit of 250 uV/m at 3 meters. My rough back-of-the-envelope calculations say that WIPZ must have been operating at around 5 watts of effective radiated power. Generally speaking, anyone who wants to broadcast in accordance with Part 15 should keep their power under 100 milliwatts (.1 watts).

I’m a little surprised that anyone at a university station would think it was legal to broadcast with that much power without a license. FCC Chicago district director James M. Roop told the Journal-Sentinel, “Somewhere they were misinformed by people who told them that operating a station by low power would be OK.”

I’ve seen a number of references to WIPZ being a carrier-current station, which is a type of very-low power AM broadcasting where a building’s electrical wiring is used as a big radiator for an AM signal. Schools are permitted to operate carrier current stations provided their signal obeys Part 15 limits with regard to the signal’s transmission off school property. WIPZ probably used carrier current back in its AM days. However, there are no similar rules for FM broadcasting; there is no such thing as a carrier-current FM station.

My best guess is that the station’s management confused the more lenient restrictions for unlicensed AM broadcasting with the tighter ones for FM. Working in and around universities for some 20 years I’ve often heard misguided educators claim they can legally set up FM transmitters using several watts of power provided the signal stays on campus. But the simple fact is that this is not true.

It appears that WIPZ will attempt to return to air using power levels that obey Part 15 limits. They will probably be disappointed at how limited their broadcast range will be. They might actually be better off going back to AM and taking advantage of the techniques devised by the sizeable community of Part 15 broadcasters.

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3 Responses to College Radio 101: UW-Parkside Station Learns When You Need a License

  1. John Anderson April 5, 2010 at 9:41 pm #

    Can you share your “back of the envelope” formula for calculating FM ERP from signal strength measurements? I’ve wracked my brain trying to figure this one out (as it would allow me to estimate the power of pirate stations that are dinged for the EAD, but I suck at math), and it has eluded me….

    Thanks in advance!

  2. johnny April 6, 2010 at 3:51 am #

    me neither…help!im a also a big fan of listening to radio online stations. i hope you could help us figured it out.thanks..

  3. Dane Ericksen May 24, 2011 at 9:30 am #

    The free space formula is
    Edbu = 102.8 – 20logDmiles + 10log(Power,kw)

    For example, Section 73.310(a) of the FCC Rules (FM Technical definitions) says 1 kW ERP at 1 km gives 221.4 mV/m. 221.4 mV/m = 106.9 dBu; 1 km = 0.622 miles; 1 kW = 0 dBk. Does 102.8 + 20log(0.622) + 10log(1) equal 106.9? Yes, it does.

    334,559 uV/m = 110.5 dBu
    3 meters = 9.8 feet = 0.00186 miles
    solving for P gives 0.0000204 kW = 0.0204 W = 20.4 mW ERP (ERP is referenced to a half-wave dipole; it should not be confused with EIRP, which is referenced to a theoretical isotropic antenna).

    Of course, the above free space formula was derived for far-field conditions, and at FM frequencies 10 feet from a device is not yet far field, so the free space formula might not be valid that close in. In any event, though, Section 15.239 of the FCC rules is based on not exceeding 250 uV/m (48 dBu) at 3 meters from the device; the device’s power is irrelevant. Again assuming that the free space formula is valid at 3 meters, this gives a maximum power of -109.4 dBk, or
    -79.4 dBW, or -49.4 dBm, or 0.0115 microwatts.

    The bottom line is that if the FCC measured 334,559 microvolts/meter at 3 meters, the station was exceeding the Part 15 limit by more than 60 dB. That’s a lot.

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