Re: OpenSPOT2 Lesson Learned

Greg D

Hi Gerry,

Yeah, the WiFi industry's marketing-over-physics strategy ended up shooting itself in its proverbial foot on what a "channel" is.  More channels is better, right?  The problem is that the channels overlap, and that causes interference.  Consider multiple SSB conversations spaced only a few hundred hertz apart in a pile-up.  Nobody wins. 

In case you're interested...

The WiFi channels are actually an overlay to an older channel allocation.  The base channels are 5 mhz wide, and (802.11B) WiFi channels need about 22 mhz (20 + a guard band) of bandwidth each.  So each WiFi channel actually occupies about 5 of the base channels.  The Wikipedia page ( ) shows the actual frequencies.  The problem is that they left the original channel numbering, and let folks use all of them.  You'll see that Channel 1's allocation ends where channel 6's allocation starts.  So anyone using channels 2-5 at the same time will be interfering with both 1 and 6.  Same issue for channels 7-10 interfering with both 6 and 11.  So for best operation, one should only use channels 1, 6, or 11, but that's only 3 channels.  Marketing that you have 11 channels is better, no?  Sheesh...

If you look at the channels 5 ghz band you see that they don't allow use of the intervening channels, so they got that one right.  But on 2.4 ghz, it's a bit of a mess.  Oh, also the 2.4 ghz band is used by Bluetooth and some older cordless phones and video cameras, not to mention your microwave oven.  Bad idea to put your home WiFi router in the kitchen next to the microwave.

As to what to recommend for a default channel, it's hard to know.  As you say, many devices pick channel 6, but I've seen a lot of WiFi-enabled printers come up on channel 10.  There are cell phone apps that can give you a scan of the RF landscape, letting you pick out a quiet spot.  But, in theory, that's what your HotSpot was doing, so there's no single rule that will guarantee success.  I generally do a WiFi scan and then pick from among the three non-overlapping channels on the 2.4 ghz band, but leave the 5ghz setting to "auto" since they don't overlap.

Greg  KO6TH

Gerry - WA6E wrote:

I've enjoyed being on the road with my OpenSpot2.  It's fun to be here in Arizona and to hear what's going on back at home.  But here is something I learned the hard way about the OpenSpot2 and I pass it along in the hope that it might save somebody a headache.

Sometimes the OpenSpot would lose the connection with my Verizon Jetpack.  I would walk into the motorhome and it would be saying "Openspot trying to connect to Wifi" or something like that.  This went on and on and on.  I would have to reset everything several times to get it to work.  A little research discovered that the OpenSpot will only work on channels 1, 6 or 11 in the 2.4 GHz wifi "band."   I had my Jetpack channel selector set to "various."  I think what was happening was the Jetpack would sense interference on whatever channel we were on and move to a channel unsupported by the OpenSpot.  All my other wifi devices would follow the change but the OpenSpot would not.  So I changed the Jetpack to stay put on Channel 11 and all has been well since.

If you have this problem I would suggest you avoid channel 6.  I believe just about every wifi device comes with channel 6 as their default channel.



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