Re: Emulating a wireless access point

[Marc Mosko <marc () computer org>]

I don't know why you need to consider harmonics.  802.11 DSSS is
very susceptable to CW interference.  Each DSSS channel takes
22 MHz out of the 83 MHz in the 2.4 GHz band.  If you operate anything
in that band, you'll most likely screw the CCK modulation.  Unlike
the FH phy, DSSS needs most all 22 MHz at the same time and does not
skip to other frequency ranges (FH uses 1 MHz channels evenly spaced
over the range and hops in 3 MHz increments).  Since most cordless
phones use an "autoscan" technology they will sense interference
and move out of the 802.11 range.  Generally, they have about
30 channels spread evenly over the 2.4 GHz range.

David Ford wrote:
> This is perfectly true with the caveat that for every harmonic that you
> step away from the prime, the power of the transmission drops
> proportionately.  This is all considering there is no harmonic
> filtering, also known as a bandpass filter.
>
> Here is where you truely get what you pay for.  Inexpensive equipment
> tends to skim on features such as noise suppression and filtering.  Such
> manufacturers don't care very much if they are splattering noise across
> the spectrum.
>
> David
>
> bparis () sorrentolactalis com wrote:
>
> >       You are correct Meredith.
> >
> >       I live near a cell tower (100m away) and can clearly hear cell
> > conversations on my scanner at the 1st lower harmonic, app 450-460Mhz.
> >
> >       Getting back the the original question, cordless 2.4Ghz phones are
> > notorious for creating interference with other devices using the same freq
> > band. I recommend not operating 2.4Ghz phones in a wireless environment.
> >
> > William S. Paris
> > Telecommunication/Network Analyst
> > Sorrento Lactalis Inc.
> > bparis () sorrentolactalis com
> >
> >
> >       Actually, it probably has to do w/ the frequency / harmonic
> > resonance of
> > the phone interfearing w/the AP ... not the proximity. Even if the phone
> > operates on a different frequency, it can interfere w/ the AP via harmonic
> > resonance.
> >       Harmonic Resonance occurs when one of the frequencies is a multiple
> > of the
> > other. Say your AP operates at 2 hz ( for simplicity sake) and your phone
> > operates at 4 hz, then every other cycle of the phones frequency will be in
> > phase w/ the access points.
> >
> > ASCII Diagra:
> > |                  x -- sine peak                 As you can see, the sine
> > waves are prefectly
> > |      |   |   |   |                Phone         in-phase at 2 and 4 w/
> > respect to the phone.
> > |     | | | | | | | |
> > |        |   |   |   |
> > |_________________________________ T = 1 sec
> > |
> > |                     x -- sine peak
> > |          |       |
> > |     ....| |.....| |.               Access Point
> > |             | |
> > |              |
> > __________________________________ T = 1 sec
> >
> >       Are there any Ham operators out there that can confirm or deny this?
> >
> > -- Meredith Shaebanyan
> >
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