[Soekris] PCMCIA + MiniPCI cards in net 4511

Jim Thompson jim at netgate.com
Wed Sep 22 20:48:19 UTC 2004

Colin A. White wrote:
> OK, I believe you all and I'm just a curious layman but...
> If the two cards were set to operate at say, 10 channels apart, couldn't 
> I run two entirely separate wireless networks within range of one 
> another?  (My current setup copes admirably with interference from other 
> WLANs from adjacent buildings and I assume they cope with mine)

Likely.  (is that 10 of 802.11b's channels, (1 and 11) or would it be 
some set of frequencies 250MHz apart?  (perhaps you're thinking of 
running in the 5GHz band.)

1 and 11 will still have the problem, though less so (15-20dB less so).

> At what point would both cards try to transmit or recieve on the same 
> frequency? How does an incoming b frame get smashed by an outgoing g 
> frame if they are on different frequencies?

Because the receiver architecture isn't perfectly selective, so some of 
the signal from the adjacent channel "shows up" in the receiver.

> Or is the problem to do with having 2 antenna only inches apart and 
> would the signal gain fry both antennas? I'm only guessing here as my 
> grasp of RF voodoo is limited...

RF isn't voodoo.

> If I were to put an 11g AP right next to an 11b AP and use two separate 
> laptops to connect to each,  would I experience the problem you're 
> describing here? (i.e. neither would be usable)

If they're all close, you probably have enough SNR to be able to 
communicate, especially while the loading stays low.

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