Member Avatar for mouaadable

Hi, i bought an alfa wifi adapter with realtek rtl8187 moderboard, when i plug it to computer using 10 meters usb cable it show me the message: usb device not recognized. but it appear on Device manager and wifi management softwares (but no wifis shown) .
but when i plug it to other cables (5meters and lower) it work without problems .
what is the problem please ? this cable was workin great with my old alfa with the ralink moderboard !
thank's in advance

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  • Latest Post Latest Post by Kevin_32

Dani AI

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Brief diagnostic checklist and practical fixes that expand on the thread (references and examples follow).

If the adapter enumerates in Device Manager but the radio never scans, the most likely issues are voltage/current loss on VBUS or signal degradation on the data pair. Verify those two things before swapping adapters: confirm the adapter works on a short, known-good cable; measure VBUS and current at the device end with a USB power meter (look for the minimum voltages the USB spec requires at hub/device points); and check Windows Event Viewer or the device’s status in Device Manager for enumeration errors. (USB-IF: peripheral power rules and timing constraints).

When a long run is needed, use equipment that reconditions the link and/or supplies local power rather than a long passive lead. Options that work in practice are powered USB repeater/hub placed near the adapter, an “active” USB extension (repeater) cable with its own power, or a USB-over-Cat5/6 extender — all restore signal integrity and VBUS at the far end. Examples: StarTech active repeater cables and commercial USB-over-Ethernet extenders like Gefen. (StarTech active extension example) (USB-over-Cat5 extenders example). Passive USB 2.0 and SuperSpeed cable length limits and practical tradeoffs are summarized by cable specialists. (CableMatters summary).

A quick proof test: put a small, powered USB hub right at the adapter end and see whether scanning returns. If that fixes it, the problem is power drop; if not, try an active repeater or USB-over-Cat5 solution. This approach builds on and ’s observations while giving concrete measurement steps and deployable alternatives.

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Member Avatar for rproffitt

That's beyond the distance we expect USB to function. Yes it might work with say an older device if said device was different in any way (USB 1 vs 2?)

To fix this I'd try those "10 Meter (32 Foot) USB 2.0 Active Extension Cable" versus a simple cable.

Member Avatar for mouaadable

no both of the devices are 2.0 (my old adapter and this adapter)
all posibilites are :
my rtl8187 + 10 meters usb cable = usb device not recognized
rtl8187 + 5 meters + 1 meter usb cables = working very well

rtl8187 + 1 meter usb cable = working very well

my old ralink + all usb cables = working very well

Member Avatar for rproffitt

You're falling for the old trap that old worked, why not new. That is, it's beyond the USB spec and as such can be hit or miss. I don't see if you tried an active cable.

Member Avatar for rubberman

A USB cable that is more than 10 feet long (3+ meters) is going to be dicey at best. The fact that it worked with your old WiFi gear was luck. 5 meters (15 feet) is already getting to the limits of the tech for unaugmented (non-active) cables.

Member Avatar for mouaadable

thank's guys, what do you advise me with ? any specific type of wifi adapters tha tsupport 10+ cables ? is usb 3 .0 do that ?

Member Avatar for rproffitt

Sorry but you were lucky with the first one. It's not the adapter but luck here. Look again at the USB spec then try those active USB cables.

If you are looking at some WiFi client thing you can put away from a PC, maybe Ethernet? Look at what I used last time. The Netgear WNCE2001. There are things like that on Ethernet which can be far away from the PC.

Member Avatar for mouaadable

alright, thank's alot
i really appreciate it .

Member Avatar for mouaadable

update : i bought the edup ep 8523 and it's working great with 12 meters cables(10meters+2meters) it also come with 5 meters cable included, it's only usb 2.0 .

Member Avatar for Hamza_18

mouaadable is edup ep 8523 good like alfa wifi adapter or better ?

Member Avatar for Kevin_32

Have you tried another usb chord btw?

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