[CUWiN] good news everyone

Bill Comisky bcomisky at pobox.com
Sat Aug 5 14:37:31 CDT 2006

On 8/5/06, Aaron Kaplan <aaron at lo-res.org> wrote:
> > hard disk, like a PVR.   How complicated is that?
> >
> (...) i did not mean this question :)
> > For the 1 thousandth time, we need a directional rooftop
> > device, of which, each house needs two or more, in
> > order to construct our urban mesh WHOEVER we want.
> >
> oops!
> yes, i agree. But I think I have to clarify what I acutally meant:
> _given_ that many freifunk/funkfeuer/cuwin meshes are like they are now,
> and _given_ that our projects attract media attention and therefore - as
> it happend in VIE now - the attention of the (local) FCC
> ("funkueberwachung", "regulierungsbehoerde" in germany) and _given_ that
> - as you are all freaks - you installed high gain antennas.
> THEN not everything is lost. You can still use these nice 24dBi high
> gain antennas on the manner i described before.

The FCC is a more lenient for fixed point-to-point installations;
see Title 47, part 15, section 247 of the Code of Federal Regulations:

Note also the allowed EIRP by the FCC is a lot higher than 100mW..
1000mW with a 6dB antenna for multipoint links == 4000mW EIRP.

See below for a quick summary of the regulations from Tim Pozar

3.1.1 - Point to Multi-point
For 802.11b point to multi-point uses, you are allowed up to 30 dBm or
1 watt of Transmitter Power Output (TPO) with a 6 dBi antenna or 36
dBm or 4 watts Effective Radiated Power over an isotropic antenna
(EIRP). The TPO needs to be reduced 1 dB for every dB of antenna gain
over 6 dBi.

3.1.2 – Point to Point
For 802.11b point-to-point uses, the FCC encourages directional
antennas to minimize interference to other users. The FCC in fact is
more lenient with point-to-point links, as it only requires the TPO to
be reduced by 1/3 of a dB as compared to a full dB for point to

More specifically, for every 3 dB of antenna gain over a 6 dBi
antenna, you need to reduce the TPO 1 dB below 1 watt. For example, a
24 dBi antenna is 18 dB over a 6 dBi antenna. You would have to lower
a 1 watt (30 dBm) transmitter 18/3 or 6 dB to 24 dBm or ¼ watt.


Bill Comisky
bcomisky at pobox.com

More information about the CU-Wireless mailing list