iPod photo interference issue traced, explained

Third-party iPod developer Engineered Audio, maker of the RemoteRemote 2 RF remote control system, has provided to iLounge an excellent explanation of the radio frequency (RF) interference issue affecting certain iPod photo hardware. The company’s findings follow up on iLounge’s exclusive March 31, 2005 report, “Yes, the new iPod photo -is- different,” in which we detailed an interference issue that prevents current RF-based remote controls from fully working with “first-generation” (pre-February 2005) 40/60GB iPod photos. As a result of the interference, the RF remotes work at only one-sixth to one-twelveth of their performance ranges with all other iPods.

“The current crop of RF remote controls for the iPod operate at or near 433.92 Mhz,” explains Engineered Audio. “The reasons for this frequency choice are not particularly relevant, except to say that this particular frequency is usable (or certifiable) in the US and in Europe. Further, most of the receivers for these remote control systems are simple super-heterodyne or super-regenerative. And without very careful filtering at the antenna, both types may suffer a degradation in performance when there is a nearby noise source.

“In this case the iPod photo is generating an undesirable RF noise source at 432.00 Mhz (see plot 1). Some might consider the difference between the two frequencies to be enough to not cause interference, however, this is simply not the case. Most of these simple receivers have a fairly wide bandwidth with relatively high gain, and so are easily swamped by an interferer that is within a few megahertz of desired signal. What’s inside the iPod that is generating this signal we can only guess at (perhaps an harmonic of the primary clock for the processor…) At any rate, it would appear that Apple has since modified the iPod photo to either reduce or eliminate this particular signal.” A spectrum analysis photo (“Plot 1”) and additional details are available by clicking on Read More below. We thank Engineered Audio for explaining the interference, and all iPod RF remote manufacturers for being forthright with consumers about the incompatibility.
The RF interference issue is believed to affect only “first-generation” 40 and 60GB iPod photos, which included packed-in accessories such as an A/V cable and iPod photo Dock in their boxes, and not “second-generation” 30 and 60GB iPod photos that ship without those items. iLounge has previously requested comment from Apple regarding audio interference affecting certain iPod photos and fourth-generation iPods, but still has not been updated on the status of units shipped to Apple in 2004 for testing.

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