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Sprint U1901 - would I benefit from outside antenna

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  • Sprint U1901 - would I benefit from outside antenna

    I just switched from DSL to Sprint 4G service (was getting poor DSL speeds at my location - 1.2/.5 - but now getting a consistent 5.5/1.2 with my Sprint U1901). The modem is currently installed at the end of a 12-foot USB extension cable, sitting on a shelf - the best hot spot I was able to find in my home. I'm running it into a Cradlepoint router and it is working very well. My only complaint is the modem is very tempermental when it comes to location. If it gets moved even a couple inches when someone dusts the shelf the speeds go right out the window.

    As a "quick fix" I purchased a USB performance dock. I figured worst case it would at least keep the modem in one place. However, it made matters worse. Speeds dropped to .85/.3 and the modem kept dropping its connection. I figure the loss from all of the extra USB cable and connectors was causing issues. Either that or I just got a bad modem (it was brand new from eBay, still in its manufacturer's shrink wrap. It was the Clear version and not the Sprint one, but theoretically that should not have made a difference).

    I have also seen some other people post 4G download speeds closer to 10. I get there on occasion but 90% of the time I'm running in the mid-5 range. I can't help but wonder if I can't get the speed up a bit with a little tweaking.

    My RSSI is -63 and my CINR is 24, both pretty good numbers from what I understand. Would I benefit from an outdoor antenna? I'd be curious to hear if it would help with speed even if I already have a good signal indoors.

  • #2
    the modem is very tempermental when it comes to location. If it gets moved even a couple inches when someone dusts the shelf the speeds go right out the window.
    This is unfortunate but we have seen it quite often. We think it has more to do primarily with MIMO antenna orientation rather than general poor weak received signal strength (RSS). This is especially true for a rich multipath environment where MIMO multiantenna diversity really boosts performance. Unfortunately a small change in the modem orientation could drastically change the correlation of the signals that go to the two antennas. And by a small change I mean a fraction of a wavelength (and recall the wavelength of a 2.6GHz signal is about 12cm!).

    As a "quick fix" I purchased a USB performance dock. I figured worst case it would at least keep the modem in one place. However, it made matters worse. Speeds dropped to .85/.3 and the modem kept dropping its connection. I figure the loss from all of the extra USB cable and connectors was causing issues. Either that or I just got a bad modem (it was brand new from eBay, still in its manufacturer's shrink wrap. It was the Clear version and not the Sprint one, but theoretically that should not have made a difference).
    This is odd. I highly doubt is has anything to do with the USB cable/connector. The most critical path is the RF path. By the time the signald has been down-converted and demodulated and the baseband data stream and when it gets onto the USB cable it is not too dependent to cable lengths or connector impedances as it is when it's a high frequency RF, provided of course the cable length is within USB protocol limits which it is.

    You are right clear vs sprint is just the branding - they both use the same network. I couldnt rule out the docking station being defective although we have rarely seen this. Most likely reason again might have to do with the unique multipath fading environment in the room. Somehow the multiple antenna configuration in the USB modem seems less susceptible to changes in angle of arrival than that in the docking cradle for your unique propagation environment. This again suggests your channel is very dynamic and severly prone to antenna orientation (as well as antenna correlation) which is not a good thing.

    I can't help but wonder if I can't get the speed up a bit with a little tweaking. My RSSI is -63 and my CINR is 24, both pretty good numbers from what I understand. Would I benefit from an outdoor antenna? I'd be curious to hear if it would help with speed even if I already have a good signal indoors.
    Yes absolutely. You are actually a very good candidate for outdoor antennas. Since your signal is already pretty strong, you just need to make it more stable by adding antenna gain and removing the antenna from in-building propagation environment.

    Here is our most popular antenna kit: http://www.rfwel.com/shop/4G-USB-Mod...tenna-Kit.html. A single 18dBi panel antenna on the primary antenna port will work for you. You can leave the secondary antenna to use the internal antenna.

    Let me know if you have other questions/clarifications and if you do end up getting it would appreciate your feedback on performance.
    Last edited by thuor; 04-19-2011, 11:53 PM.
    KF7RCQ

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    • #3
      Thanks for the feedback. I am definitely interested in taking a look at the outdoor antenna.

      One clarification on the Clear USB antenna dock. It looked like it improved my signal at least a little bit, but for some reason the modem kept disconnecting and re-connecting - like every 20 - 30 seconds - when installed in the dock. Like you said, it is very bizarre. I was thinking maybe it was some kind of RF interference getting into the cable. I had major problems with that when I first installed the modem into the router. The router RF was interfering with the modem and severely cutting down the speed. The only way I solved it was with about 10 feet of high quality USB extension cable. I saw the same modem disconnecting problem when I used a couple of cheap USB extension cables that I just happened to have sitting around in my stash. Or, it could just be a defective dock. Either way it didn't work for me.

      One more question on the panel antenna. I live in a fairly large condo complex. I would have no problem getting the antenna outside. It's low profile enough that I can put it on my patio and my HOA would never see it. However, since it is a directional antenna, does it need to have a clear line of site to the tower? If I mount it where I am thinking, it would be somewhat obstructed by buildings and trees. I do have the possibility of getting it up on the roof, but then I'd need considerably longer coax, not to mention I'd have to be a little more sneaky about getting the antenna up (no access to the roof without HOA approval, and approval would be tough to get for this type of antenna). I do have a DirecTV dish up there and could potentially mount the panel to the same mast if need be and run the coax right next to my tv coax, but not the preferred solution due to the long coax run required and the challenge of getting up there to do it.

      In such a strong signal area, is it just a matter of getting outdoors for some signal stability? It would be nice if I can mount it in such a way that it goes virtually un-noticed by the neighbors.

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      • #4
        Directional antennas do not necessarily need line of sight (LOS) and in any case LOS is typically very uncommon for cellular broadband data networks which includes WiMax. You do however need to orient it to the direction of maximum received signal strength which interestingly doesn't necessarily have to be the direction of the BTS tower.

        Also remember the lower the antenna dimensions the lower the antenna gain. So if you will go for example with our wide band cellular/wimax LPDA antenna or the dual band dual unity gain MIMO antenna WMM-7-27, then you may as well get an outdoor router/antenna system such as the HANA SELECT Outdoor 3G/4G Router & Antenna System. This gives you both the antenna and the router in a low-profile outdoor system and since it supports POE (power-over-Ethernet) then you need only run CAT5 cable outdoors.

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