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How to get >500 ma to USB modem? Over long distance?

 
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VanDee
EVDO Newbie


Joined: 03 Sep 2008
Posts: 9
Location: Eustis, Florida

PostPosted: Thu Sep 04, 2008 6:50 pm    Post subject: How to get >500 ma to USB modem? Over long distance? Reply with quote

As discussed in many Forum posts, most USB sources intentionally limit the current drawn by one port to 500 ma in order to protect the source from short circuits. On the other hand, many USB modems will perform “better” where the signal strength is low if they are able to draw more current, 850 ma for example. I’m still puzzled about how to proceed after browsing the Forums for several days.

1) How much difference does it actually make? Of course, it depends on so many factors that it’s hard to say anything in general but would those of you who have compared the performance of your modem with and without additional current care to describe your experiences?

2) Many posts suggest using a “powered USB hub” instead of a “Y” cable to supply more current. I’ve been reading specs on externally powered hubs from quite a few manufacturers. The ones I’ve found still limit the output of any one port to 500 ma. (The external power simply allows them to supply 500 ma to all of the output ports at the same time while ‘self-powered” hubs have to divide the 500 ma available from the input port among all their output ports.) Can anyone suggest particular hub manufacturer/part numbers that will supply more than 500 ma to a single port?

3) I would rather use ICS (Windows’ Internet Connection Sharing) than a router for the reasons given by Jim_in_VA in his excellent "evdotips blogspot com" site so I haven’t researched routers. However, would anyone care to suggest manufacture/part numbers of routers that will supply more than 500 ma for readers who are interested?

4) Many posts point out that you can often improve your signal strength dramatically by simply moving the modem to a different location. (I gain 15-20 dBm by simply taking a laptop with the modem up on the roof of my house!) How would you supply even 500 ma, much less 850, at the end of a USB bus several tens of feet long?

4a) “Active” bus extension cables up to 16’ long are available. They include electronics to restore the signals and power voltage level so several of them can be daisy-chained up to 80’. (I expect signal timing must the limiting factor?) However, the electronics in each cable have to consume some power that must come out of the 500 ma supplied by the original USB source so the modem must receive even less than 500 ma. I haven’t found a spec for how much power they use but it seems likely that multiple, daisy-chained cables might seriously starve the modem.

4b) USB/Ethernet/USB extension cables can span up to 150’ in one hop and several Forum posts indicate that the work pretty well. But, again, the power for the electronics has to come from the 500 ma supplied by the USB source starving the modem.

4c) I saw a passing comment by Jack_in_VA in one post that sounded like he’d figured out how to inject external power into a standard, passive USB cable. I can’t find it again. If anyone knows how to do that, it might be the best of all solutions.

I’m new to EVDO and these Forums. I’ve spent quite a bit of the last two weeks searching for the answers to these questions but I may not have looked in the right places. If someone can point me to answers or if I’ve just misunderstood the situation altogether, I’ll happily delete this post. If, on the other hand, the questions are interesting and the answers aren’t readily available, perhaps you’d like to use this thread to consolidate the discussion of modem power supply?
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3Gstore
EVDO Addict


Joined: 19 Sep 2006
Posts: 3158

PostPosted: Thu Sep 04, 2008 7:28 pm    Post subject: Re: How to get >500 ma to USB modem? Over long distance? Reply with quote

VanDee wrote:
...would anyone care to suggest manufacture/part numbers of routers that will supply more than 500 ma for readers who are interested?
cradlepoint engineers have told me that their usb ports will provide nearly 1000ma
VanDee wrote:
...I gain 15-20 dBm by simply taking a laptop with the modem up on the roof of my house!) How would you supply even 500 ma, much less 850, at the end of a USB bus several tens of feet long?
if you can get that with just the usb modem's antenna, you can get better using a high gain antenna and run low loss cable to where you want to have usb modem, and still have significant signal. that would make more sense to me.
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JGriggs
EVDO User


Joined: 04 Dec 2006
Posts: 93
Location: North Central Indiana

PostPosted: Thu Sep 04, 2008 7:33 pm    Post subject: Reply with quote

4.3. You need to be good with electronics.
Cut the sheath off the cable without damaging the conductors below.
The cable colors should be red, black, green, and white.
Cut the red (+5 Vdc) and black (ground).
Safely terminate the pair coming from the computer.
Inject your 5 volt supply in the device side red and black lines.

4.2 You need an usb to Ethernet extension that has a self powered hub at the end, if you can provide power there.
I didn't look hard, but this one has the power port in the picture.
I don't think it comes with the adapter though.
http://www.cyberguys.com/templates/SearchDetail.asp?productID=11251

You could put a self powered hub at the end and save some trouble, though.

3) I used ICS for about a year and a half.
I purchased a CradlePoint 500 recently from 3GStore.
I will never go back.
The router made everything easier.
I can position it where I want.
There are no cables to mess with.
Finally, I personally am getting better speed too.
(Mostly because of positioning.)
I think you will find that these routers will provide more than 500 ma, too.
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VanDee
EVDO Newbie


Joined: 03 Sep 2008
Posts: 9
Location: Eustis, Florida

PostPosted: Sat Sep 06, 2008 5:56 pm    Post subject: re: Routers Reply with quote

Thanks, Alex, for the info that Cradlepoint's routers can supply so much current. I couldn't find that information on their web site.

Jim_in_VA has said that he prefers using ICS because ##DEBUG doesn't work if the modem is located in a router. Do you know if that's still true? Do you miss it or don't you use it much once you've got your installation working well?
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VanDee
EVDO Newbie


Joined: 03 Sep 2008
Posts: 9
Location: Eustis, Florida

PostPosted: Sat Sep 06, 2008 6:47 pm    Post subject: re: How to supply > 500 ma Reply with quote

I can't find a max output current/port spec for the VAD-1140 JGriggs suggested on Vigor's web site. However, since the optional external power supply is spec'd at 2A and has to power 4 ports, the output/port is probably limited to 500 ma.

USB sources need to explicitly limit their +5V output current so they aren't damaged by short circuits. The USB spec says loads shouldn't draw more than 500 ma so it's probably going to be hard to find a source that will supply more unless it was designed for a particular, out-of-spec application like the MBRs.

You're probably right that fooling around with long and/or hacked USB cables is never going to perform as well or be as trouble-free as an external antenna. I really had in mind putting the modem in the attic rather than outside so it wouldn't be exposed to weather. However, the attic heat would probably cook it anyway. Sigh.

I'm still intrigued by the USB possibilities and will pursue them a little. I chickened out on hacking USB cables. Ordered a "Y" cable. Will try to pin down how much difference the additional power makes, if any and report the results in a week or so.
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