We are establishing a net in fairly dense suburban area. The terrain has several shallow valleys and ridges (old creek routes) and a large number of trees. Average distance between nodes is between 1 and 4km. We are operating on Channel 1 with a 20mHz channel width.  We have been trying a variety of radios and antennas and seem to have reached a point that we cannot improve beyond in the current configuration.

I have been thinking about two areas where we might get improvement and would like to know if others in our situation have tried these changes, and what the results were.

#1. Switch to a smaller channel width? A little testing here seems to suggest lowering channel width does improve LQ (with a commensurate loss of throughput). Is there any "science" to this? Are there issues in asymmetric operation in which two sides to a link operate at different channel width settings?

#2. Observations with Wi-Fi scans from various locations indicate channel 6 is less crowded than channel 1. Have any group tried switching to channel 6 in an area like ours? Did the expected improvement actually materialize?

Thanks

Richard - wb6tae

The science behind decreasing the signal width is one primarily of power density, that is, you are putting out 600mw of power across 20MHz it is 600/20=30mw/MHz density, while 600/6=120mw/MHz density. 

The increased density in theory should do two things 1) Increase the power as seen on the receive side as the power is spread out over less space its being more focused (similar to a high gain antenna that focuses the energy into a couple of degrees instead of an Omni pattern)  and 2) By decreasing the width of the signal the overall noise should (in theory) get smaller as you do not have to let as much noise into the system to get the whole signal (5MHz of white noise vs 20MHz of white noise.)  Both of these should cause the SNR to increase over the entire chain. 

Now the trick for this is ALL nodes have to run the same channel width, a 5MHz node can not talk to a 20MHz node,  as they are not receiving the signals the same way.  You can use DTDLink to jump between networks links that are different widths (one node runs one way another runs the other) but no single node can run on both at once.

As usual, thanks!

In some very basic testing, I changed only one side of a link to 10mHz and left the distant side at 20mHz. The link stayed up and the quality went up by 15 to 20%. This would indicate that either tx and rx channel width can be independent or some accommodation is going on.  Any thoughts?

BTW, I just "Apply"ed the change. I did not do a save and reboot.

You likely just ran into a link stability increase caused by other factors.

The channel width setting only takes effect upon a combination that includes a save (officially this means save and reboot) not upon an apply.

Also the SSID Changes as well to ensure this can't happen (even if the hardware some how fails and starts leaking the data across as was reported at one time in the Linux Kernel archives)

That makes sense. Perhaps someone with the right knowledge might revise the Setup Help page to clarify which changes can be "applied" and which require a save and reboot. The current wording implies that all changes in the Wi-Fi box can be applied.

Richard - wb6tae

I can see how that might be interpreted that way. Perhaps we can make it a little more clear in a future build. It is only suppose to be the settings in the "Active Settings" subbox that the apply button applies too.