I was recently using the AirMagic feature on a backhaul link and it was nice enough to tell me the bits per Hz and calculate total potential bandwidth at different channel widths. It claimed that I would actually get more bandwidth on a 20MHz channel as opposed to a 40MHz channel down that same path. I tried it and sure enough! AirMagic is amazing. Now if they would just get 8.0 firmware solid enough that I could be confident running it everywhere.....
On Thu, Jun 16, 2016 at 8:37 AM, Ken Hohhof <[email protected]> wrote: > Yes, except you are counting the 3 dB twice. > > If you look at it from the total power perspective, signal stays the same, > noise is cut in half. If you look at it from the power spectral density > perspective, signal is double, noise stays the same. > > In some bands the regulatory limit is on psd not total power, so you don’t > gain any system margin with a narrower channel, you just lose throughput. > > > *From:* Forrest Christian (List Account) <[email protected]> > *Sent:* Thursday, June 16, 2016 9:18 AM > *To:* af <[email protected]> > *Subject:* [AFMUG] Power limits per hertz. > > > I've had a couple of conversations over the past little bit which has > gotten me thinking about power limits in relation to channel width. > > This is my thinking. Assume 5.8ghz, ap side. Power limit 36dbm. > > My question/thought/potential misunderstanding has to do with how that > 36dbm is measured. Assuming you're comparing a 20 mhz channel with a 10 > mhz channel, both at EIRP limits, does the 10 mhz channel effectively have > more Power density? > > Assuming this is the case, it seems you would gain 3db of link margin for > the increased power density and 3db more for reduced noise floor. 6db is > double the distance which is big, even with the reduced throughput. > > Is this the way this works? >
