More On Wired FM Direct Adapters For Satellite Radio

Commentary: Why Some FM Mods Go Over Limits
Wired FM Modulators Are the Best Technical Solution for the Bleed-Through Problem
by Mike Bergman, 9.13.2006 (The author is vice president of new digital technologies for Kenwood USA.)

Recent tests conducted by the NAB and NPR have raised questions regarding wireless FM modulators. Some of these products are apparently over FCC Part 15 limits.
The view of this situation is somewhat different, depending on whether one is a broadcaster or a consumer electronics maker, for obvious reasons. As manufacturers, we generally look to comply with existing regulations as much as broadcasters do, but recent events have shown that not all regulations are being observed, or at least not with the same attention to detail.
When we're discussing wireless FM modulators, or "mods," we're generally talking about the low-power intentional radiating devices that are expected to transmit a weak signal a short distance to an FM receiver. By "short distance," I mean perhaps a meter or two. FCC rules are located in Title 47 of the Code of Federal Regulations. CFR 47, Part 15 covers these items. Part 15.239 and Part 15.209 cover the requirements under which these devices operate, with measurement specifications in several places including ANSI/IEEE standard C63.4.
Was I speeding, officer?
Many consumer applications for these modulators are for the mobile (car) environment - using a modulator to play your iPod, for example, over your OEM car stereo. A wireless modulator that strictly complies with Part 15 limits will sometimes have noisy audio in a real-world environment.
The device would need higher than Part 15 power to get clean performance under the majority of normal conditions. Markets such as New York City don't have any open channels, so there is an ongoing motivation for transmitting higher power.
Put another way, the existing Part 15 limits don't allow for reliable transmission enough of the time that consumers will be happy with the product. This leads to consumer calls and complaints - on the CE side. Of course, transmitting too much power leads to calls and complaints to the broadcasters, and eventually a letter from the FCC...READ MORE: HERE

9/17/2006 09:48:00 PM

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