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FCC Conducts Additional Tests on 'White Space' Devices
1/25/2008

FCC testing of "white space" devices (WSD), which are designed to find vacant TV channels and use them for broadband and other wireless communications, officially started Thursday, Jan. 24 (see last week's RF Report for the test plan). Almost 20 observers showed up, not including proponents and FCC staff.

Thanks to a reader who observed the testing, I'm able to share the results of the first day's activities, conducted at the FCC's Columbia, Md. laboratory.

First, each proponent introduced their respective equipment and answered questions about its capabilities. FCC staffers Steve Jones and Tom Phillips outlined the first two tests to be conducted: the detection of a pristine ATSC signal (generated by a Rohde and Schwarz SFU) and recognition of an FM wireless microphone to determine channel occupancy.

The Adaptrum and Microsoft boxes include transmitters. The Microsoft unit requires the use of external filters on the transmitter, which will limit the number of channels that can be tested. If interference results are based on the use of these filters and the FCC creates rules based on the results of these tests, they will have to require any production units to meet the same emission mask. This may be difficult for manufacturers, depending on the size and complexity of the filters.

The Philips representative indicated that their device could detect ATSC, NTSC and wireless microphone signals, but it requires at least four minutes to scan the band 30 times.

Motorola said their box took only 50 seconds to scan the entire band 100 times, but NTSC signal detection wasn't specified. It seems to me if a box is able to detect a wireless microphone, it should be able to detect the aural carrier of an analog TV signal.

LPTV and TV translator licenses, which don't have to shut off analog transmissions in Feb. 2009, would welcome detection of analog TV signals, but that wasn't in the test plan.

In the testing, both the Microsoft and Philips boxes demonstrated better sensitivity than was expected. It wasn't clear why the devices performed differently, but observers didn't see any evidence of problems with the FCC test equipment or methods. The Philips box reliably detected a pristine ATSC signal as low as -122 dBm, and the Microsoft box was able to reliably detect an FM wireless microphone signal as low as -130 dBm.

If any other readers have an opportunity to observe the testing, please drop me an email with your comments.
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