Yup, that's what I thought. I'll go dig it up.
The analog filter is something on the front end, just before the transmit/receive RF side. It acts as a filter to ensure (a) decent rejection of adjacent channel signals being received and (b) the transmit spectral mask is being met. -a On 27 August 2014 21:00, Bart Kus <m...@bartk.us> wrote: > Well I'll be damned, looks like 5MHz mode on Mikrotik is just slower > signalling! All 52-subcarriers are indeed there, although a little hard to > see: > > > > If you count peaks left/right of center, you'll get 26. 2*26=52, so > that's every sub accounted for. > > Can you point me at your 5/10MHz docs? And which analog filter you're > referring to? > > --Bart > > > > > > On 8/27/2014 4:47 PM, Adrian Chadd wrote: > > On 27 August 2014 16:38, Bart Kus <m...@bartk.us> <m...@bartk.us> wrote: > > I'm guessing the chip generates its own internal clocks from an external > reference. Can that PLL be slowed down ahead of timers overflowing? > Hopefully the PCI clock is generated independently. > > Yeah, that's what you're slowing down - you program the PLL. > > The PCI clock is generated separately. > > > Also, I think Mikrotik implements narrower bands by dropping subcarriers > instead of slowing down their symbol rates. I'll try to get a good spectrum > picture of their 5MHz mode tonight. Keeping the subcarrier symbol rates > relatively higher might offset some analog droops, at the cost of OFDM skirt > sharpness. > > Hey cool, if they're doing that then I should likely go digging for > the PHY documentation for the AR5414 and find out. > > > Also, a slight correction. I think you meant the subs are 312.5kHz wide, > which would result in a 200kHz emission having 3.125kHz wide subs. Or, > perhaps more realistically, running at 1/128th the speed, 2.44140625kHz > wide. How can you not love a number like that? :) > > Someone else can do better math, I'm busy doing non-wifi at the moment. :) > > But, it really is 20MHz / 64 carriers == each subcarrier width. > > > Does the project have a map of all these clocks + timers which might need > tweaking for spectrum reduction? I know you can't cite original Atheros > docs, but perhaps there's been derivative documentation works created? > > Not at the moment I'm afraid. I haven't really dug into that level of > detail. I documented what's needed for 5 and 10MHz modes. > > However - there's an analog filter that I don't know if it's > programmable or not. It's used for both transmit and receive > filtering. I know on these chips it can do 5/10/20/40 but I don't know > if it's an arbitrary width. > > > -a > > > _______________________________________________ email@example.com mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-wireless To unsubscribe, send any mail to "freebsd-wireless-unsubscr...@freebsd.org"