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Brian DipertEDN Senior Technical Editor Brian Dipert exposes, analyzes and
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Friday, September 22, 2006

Modulation Satisfaction

Sep 22 2006 12:19PM | Permalink |Comments (5) |


My wife and I spent a lot of time in our vehicles this summer, traveling around PST and the broader USA. Our Creative Labs Zen Micro and iRiver H10 portable players, and the Yahoo Music Unlimited subscription service that powers them, therefore got quite a workout. Ordinarily I'd use a cassette adapter to pipe their audio output over the car's sound system (among other reasons, because a well-maintained cassette head has a wider frequency response than a broacast FM signal, although arguably an auto's high ambient noise makes any theoretical cassette adapter advantage moot....or is that mute?), but our '01 Volkswagen Eurovan Camper's Pioneer-branded radio integrates a CD player, not a tape deck. So I had the chance to try out several FM transmitters.

I'd used a Belkin TuneCast in the past, and it worked pretty well in the Eurovan. But it chewed up AAA batteries at a rapid clip. Belkin's followon TuneCast II had several advantages over its predecessor, at least on paper; it could alternatively be powered via a cigarette lighter socket, and it supported a greatly expanded range of broadcast frequencies. But its broadcast signal intensity seemed to be very weak, judging from the fact that even a far-away radio station on the same frequency would overwhelm it and, in the absence of any other comparable-frequency signal, its output was still 'hissy'. Plus its monochrome LCD display was hard to read and annoyingly flickered, especially after the unit was exposed to sunlight for a few minutes.

The iRiver AFT-100, on the other hand, is an outstanding FM transmitter. At the time I bought one for the Eurovan, it was $29.99 at Amazon.com (right now it's $36.39). It's got a very strong broadcast signal, with a wide range of user-selectable broadcast frequencies, and its blue-background illuminated LCD is easy on the eyes. It plugs directly into the cigarette lighter socket, minimizing the number of wires cluttering the car's interior. And it automatically turns on and off based on the presence or absence of a signal coming from whatever device is connected to the AFT-100's headphone plug.

I don't know why the TuneCast II is such a feeble performer. Maybe I have a bad unit, although other reviews I've read on it echo my observations. Similarly, I don't know why there's such a stark contrast between it and the AFT-100. Perhaps the iRiver unit's broadcasting beyond FCC-specified signal strength; some of Sirius and XM Radio's units recently got busted for such a transgression. Although given how long the AFT-100's been in the market, I doubt it's misbehaving.

Those of you with iPods, who might therefore be interested in a FM transmitter that also (for example) powers the portable player or controls the iPod's volume through its proprietary connector(s), should check out a recent multi-unit roundup published by Macworld. Also check out the Ars Technica commentary on a recent survey of the number of automobile owners who listen to portable player-housed music while they drive, which provides a future forecast of what kind of portable player integration (whether iPod-specific or more generic) they'll expect going forward. And here's an article on iPods-in-cars from Wired.


Reader Comments



at 9/26/2006 9:39:25 PM, Paul Rako said:
Glad to see you liked the iRiver unit. I designed a power supply for a similar iRiver unit that would charge the player. My buddy works as Aerielle, the outfit in Mountain View that makes the transmitter. They say Belkin gave the whole FM transmitter method a bad name.



at 9/27/2006 1:08:41 PM, r said:
this is clearly a result of broadcaster complaint and resulting FCC action. MOST of the GOOD FM transmitters exceeded the guidelines. This is why new Sirius and XM items seems so weak and why large companies like Belkin have to comply. FCC is out hunting now, so it is a matter of time for other players. Why is this? A misguided attempt by broadcasters to block Satellite radio while hurting consumers. Few consumers will experience interference from these devices, but now all have to suffer. What is needed is a modified standard as this one was made long ago before these uses really mattered. So complain to the NAB



at 9/27/2006 1:25:18 PM, Inspector Gadget said:
It's not "clearly the result of exceeding the limits". The main difference here is that the iRiver's antenna is the entire length of the audio cable (via a patented coupling process held by Aerielle, Inc.) The Belkin unit has a much smaller antenna aperture. Almost all these devices use the same Rohm chip to do the transmitting, and it's hard to exceed the limits unless you start putting in extra transmitter amplifier stages, and that raises the cost.



at 3/22/2007 1:08:19 PM, Boston_Engr said:
I had one of these 2 yrs ago. Every time the mp3 audi dipped, the transmitter would shut off. I cannot recommend this. It cost be around $80 at the time, and I finally broke it, trying to figure out why a car-powered unit would even need a power down circuit. I recommend this device for the Darwin Awards of 2006



at 3/22/2007 1:28:38 PM, Brian Dipert said:
Dear Boston_Engr, maybe to avoid interfering with nearby broadcasting FM stations, or other cars' FM radios, when you don't intend to use it (I 'spect it's an arcane FCC requirement)? Or to extend its operating life? Indeed, you need to have the input signal at a reasonable level to keep it 'awake'. But it doesn't immediately go to sleep in-between tracks, or anything like that; there's a reasonable delay. And every other FM transmitter I've ever used, I'm pretty sure, has the same sort of feature.

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