High power requirements of Realtek RTL8187L chipset, found in the ALFA AWUS036H USB wireless adapter, can cause ”on and off cycling” and/or dropping of connections and performance issues (see details below). We have two solutions:
1. POWERED 4-port USB 2.0 hub with an AC adapter
2. USB cable with two A-male connectors: This resolves some power issues for Alfa AWUS036H
3. USB Cable Extender over CAT5/6 cable (up to 60-meters) with power supply (sold separately)
DETAIL: The Realtek RTL8187L chipset, found in the ALFA AWUS036H USB wireless adapter, is quite power hungry. That is, it draws much more than 500ma when operating. USB controllers are rated for 500ma per port and most will shut down the port when the load exceeds ~550ma. This causes a constant “on and off” cycling of the device in some cases. The fix is simple… Purchase a POWERED 4-port USB 2.0 hub… one with an AC adapter to provide external power. The AC adapter is rated to provide 2000ma of power to drive 4 ports @ 500ma each, but will supply a single port with up to 2000ma…. more than enough power to satisfy the Realtek chipset. This has resolved the problems of performance and signal dropping for our customers.
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Customer comment: I bought a 2 male to 1 female unpowered hub (Sima Model SUO-150, price locally $9.99) that is said on the package to be suitable for “Connecting a power hungry product, such as portable hard drives. The red USB connector connects to your computer for additional power.” Nowhere does it say how much power it will handle, however. I assume that the second male connector (red) has pins for power only. I connected the Alpa and it works fine using this y connector.
THE SAME CUSTOMER HAD PREVIOUSLY MADE THE COMMENTS BELOW (proven not true by the experience immediately above):
Customer comment: Regarding power consumption of the device: the post above may or may not be correct. It would seem to me that at 5.0 volts, a 500 ma limited USB port is still putting out 2.5 watts (5 x 0.500), which should be more than enough to power any class C amplifier (nominally 70% efficient), and most class B amplifiers (nominally 40% efficient), to 1 watt output. Also, I note on various bulletin boards that the older 500 ma Alfa unit used to be shipped with a “Y” splitter USB cable, so that the unit could be plugged into 2 USB ports at the same time. However, the newer 1 watt unit does not come with that split USB plug. This suggests that Alfa has improved the efficiency of the unit so that less than 2.5 watts input power is needed to drive it to a full 1 watt output. What are your thoughts on the need to use either a split USB cable fed from 2 computer USB ports, or a powered USB hub? (It is hard to use a powered USB hub when operating the computer in the car or at other places away from 115 vac connection.). If you suggest using the powered hub, can you suggest any that can be powered by typical “D” cells, to avoid need for 115 vac?
I was the one who originally sent the email above. I received an email asking to explain how I came to my conclusion above.
I modified a USB cable by cutting and splicing the 5v line with two “pigtails.” These were connected, in-line, with my Fluke DVM to read the actual amps running through the 5v line. Perhaps not the most accurate setup, but it gave me a good idea as to the power consumption of the adapter. The actual load fluctuated between ~550ma and ~605 ma, depending on the distance to the access point. Since the “y” connector would theoretically allow a 1000ma load, it solves the problem of the ~600ma load the adapter creates. Remember 1000mw is the transmitter power, not the power consumption of the RTL8187L chip, it apparently needs more than the supply from just one port. My solution was a powered 4 port hub, as I couldn’t find the Y adapter cable.
FROM ANOTHER CUSTOMER who had issues with the power requirements:
I have read the forum about using a powered USB hub and i have one which i tried, but it seemed to still give an error when using only one usb port. I then used a Y type usb cable and it appears to be working from the hub with that.
Comments from customer - very technically proficient - regarding a related issue: Some Active USB cables (from the same batch) work fine and others do not supply enough power for AWUS036H:
The voltage is supposed to be 5V from a USB port, but if the variance of voltage is anything like 12V (which could be anything from about 10.5-13), the voltage on different computers could be as low as 4.5. The lower the voltage, the higher the amp draw that is needed. So might be why on come PC’s all is OK, and in other cases, the issue shows up….
The extension cables we take back, in general, work fine for us on the PCs we try. It is definitely a variance in PCs that causes the issue. We ask customers to try the extension cable with a USB memory stick if they are having issues with it connected to AWUS036H: It always works OK for the USB stick. So, it’s some sort of voltage issue and not sure if it’s the extension cable that is overly sensitive to the voltage or the AWUS036H.
The extension cables we take back, in general, work fine for us on the PCs we try. It is definitely a variance in PCs that causes the issue.
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