Monday, November 23, 2009

Another link in JBad

Hameed and Rahmat are fabbing up a storm with new links these days. As the density increases, we are rapidly reaching the point where the reflectors on the tower in JBad are blanketing the city in every direction with RF and we don't need any more reflectors on the tower for new links.

Here's some photos from the latest 4km link:

Well done boys!

Saturday, November 14, 2009

Real signal strength and antenna gain numbers

Jesse from VT recently sent me back some bench test results for the WRT54GL that finally confirm our assumptions about output power and the effect of power settings in OpenWRT.

According to ye olde spectrum analyzer, the output power is a smidge lower than the 84mW that is commonly stated on the interwebs. Jesse recorded 13-15 dBm over the width of ch1 after passing through 4 connectors and about a foot of cable. Assuming 1/2 dBm loss per connector and a touch more for the cable, output is roughly 18dBm for ch1. As expected, the power settings in OpenWRT had no effect on output. Although we didn't measure all the channels, Jesse suggests that the radio is likely a little stronger in the center range (maybe even as stong as the full 19dBm we'd expect).

Jesse further verified that the Power settings in OpenWRT had no effect on output.

Thanks to all this info we can now firmly state the gain on the large antenna is 13.5-14dBi.

[Edit: a picture says 1000 words. Here's the photo of the bench test setup that yielded that data above. As can be seen from the photo, the tested antenna is the weaker of the two. Jesse is hot on the trail of another test using the other antenna so we can compare.]

Sunday, November 1, 2009

The Wachusett 10k

Lots has been happening in Fabfi land lately. Notably, we're almost at a 2.1 release that includes a built in splash page for LAN access and some fixes to mesh DNS entries. There was also some work on a feed element for the big Fabfi that could have gone better, but the big news is a new link record for the 4' reflector:


It's no world record by any means, but it is a new record for FabFi. Signal strength checked in at -77dbm, and ETX was nearly 1, though the bandwidth came back as only 747kbps--unexpectedly low for such a low ETX.

At any rate, the signal data here is completely consistent with what we see in Jbad. Depending on what our radio is actually putting out (19 or 24dBm), we have a reflector gain of either 11 or 13.5 dBi. some day we'll actually figure out the radio thing, I promise. More later (with pics), gotta get to class. (oi!)