EVDO modem with max output power?

toughguy99 · EVDO Fledgling Joined: 20 Dec 2007 Posts: 13

Hi,

I've never owned EVDO before so I'm looking for advice. This question isn't specific to PCMCIA/ExpressCard modems, but I couldn't find a place to post questions that apply to both PCMCIA/ExpressCard and USB modems.

I noticed some (all?) EVDO modems have auxiliary power sources. In some cases they have two USB cables; some have a LiOn battery. Maybe there are external AC power supplies, too, but I haven't seen those yet Smile

I'd like to get the modem with the best broadcast power without distortion, regardless of form factor. I'll add an external antenna later if needed, but I don't want to add an amp (ruins portability).

If I want to maximize output power without distortion should make sure to get a modem with an auxiliary power source? Does it matter? Do all modems sold at 3gstore.com have auxiliary power sources even if it's not mentioned in the write-up?

thanks,
tough guy.

Alex · Site Admin Joined: 19 Sep 2006 Posts: 1899

toughguy99 · EVDO Fledgling Joined: 20 Dec 2007 Posts: 13

deparson · EVDO Junkie Joined: 30 Aug 2006 Posts: 248

I don't have an answer but if the manf. does not specify output power on their web site you could look up the FCC ID on the FCC database and see if it is provided there as part of the cert. filing.

That said, I don't think that looking for max power output will be the most accurate way to judge the performance of an EVDO card.

Alex · Site Admin Joined: 19 Sep 2006 Posts: 1899

Mackieman · EVDO Junkie Joined: 31 Oct 2005 Posts: 451

Output power is a function of CDMA power control and is handled by the software in the EVDO device and the base station you're connecting to. This is pertient for USB EVDO devices because the reason most of them come with the Y-cable is because USB spec states that a single host may provide no more than 500mA of power. Most of the Rev. A devices using Qualcomm MSM6800 chipsets or newer will pull around 850mA of power at maximum output, thus causing the device to brown out if it is plugged into a single USB host. This is also why people who are using Powerbook G4 Macs see their USB devices, "reset" a lot in low coverage. The G4 used one USB host controller for both ports. This does not affect ExpressCard and PCMCIA cards because those physical interfaces provide the power required automatically.

The EVDO device will automatically step up power as required to maintain a connection. Adding an external antenna to that will lower the amount of power required from the device by boosting the signal-to-noise ratio floor (antenna gain). So then, using an antenna to boost signal and EVDO device power output are indirectly correlated.

In sum, you really have no direct control over the EVDO device's power output; that is controlled by the device software in conjunction with the base station. What you do have control over is the ability to provide a higher quality signal via external antenna and/or amplifier to lower the amount of power the card has to use to maintain the connection.