Bandwidth on ~5 mile link w/Alfa 500 and 24dbi antenna

[ishmog]

I am having some difficulty assessing and improving my 802.11g connection bandwidth on a 5 mile link using an Alfa500 (AWUS036H) booster attached to a Mac and a 24Dbi grid antenna. My measured throughput is running at about .16Mbps, which seems low to me in comparison to what other people report being possible across similar distances, but I am unsure how to evaluate the issue or improve the performance.

The AWUS036H drivers for OS X are pretty poor and offer few tuning options or performance indicators, so I can't really tell what mode or power it is operating at and certainly can't adjust it manually. The simple bar signal strength indicator shows about 3/4 strength; at that strength, with closer connections (which is what I originally bought it for) I get a nominal throughput for the protocol, up to the speed of the backhaul (generally 1.5Mps). So, it seems like the strength is adequate, but the performance doesn't match.

I imagine it's interference causing the problem, and that I may even be overpowered for the distance, but how can I determine this? I have used KisMAC for antenna alignment and it does a reasonably job showing relative signal, but from what I have read it doesn't really provide a reliable dbm measurement or SNR. It shows a generic "signal" measurement averaging 30-35 to this station. Is there a better utility available for this chipset that would provide more relevant information?

I am also unsure exactly what hardware is running on the other end of the link; I am connecting to a marina wireless network which I know is designed for good long-distance coverage, but I am not sure exactly how good. Could this be a problem?

The only real settings available to me to change in the AWUS036H driver (have I mentioned that the OS X driver for this ****s?) are Fragment threshold and RTS threshold (both now at default values of 2432). Does anyone have any practical guidance for adjusting those to improve performance? Or are they irrelevant at that distance and power?

I'm open to replacing the Alfa with something else, but it would also have to be a USB connected booster with OS X drivers available. I do not have the option of altering the hardware at the other end of the link. The existing set up is tolerable for my purposes, but it does seem like I should be able to increase the bandwidth dramatically at the existing signal strength, so any advice anyone might offer for tuning the connection would be appreciated.

Thanks!

[ad5mb]

your range is too far for the ACK timing. your adapter sends a signal and waits for an ACKnowledgement. By the time your signal gets there, your router is already in a panic because it didn't receive an ACK. this needs to be set at both ends of the link.