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From: Derek Fawcus (dfawcuscisco.com)
Date: Thu Oct 25 2001 - 18:34:32 CDT
On Thu, Oct 25, 2001 at 10:01:52PM +0100, Derek Fawcus wrote:
> On Thu, Oct 25, 2001 at 04:42:15PM -0400, Jim Veneskey wrote:
> > I believe your radio is using the ETSI channelset?
> > As far as I know, ETSI is limited to 50mw output power.
> From memory I thought that the ETSI Class Licence was for 100mW EIRP?
Let's see just found ETS 300 328:
Section 5.2.2: Effective radiated power
"The effective radiated power shall be equal to or less than - 10 dBW (100 mW)
7.2.3: Effective radiated power
Duty Cycle (x) = (Tx on / (Tx on + Tx off))
Also x is limited: (0.1 <= x <= 1),
EIRP = A + G + 10log(1/x)
Where A = Power in dBm, G = antenna gain in dBi
Now ignoring the I(sotropic) for the moment, and just considering the ERP, I could take my 340 PCI card, add an antenna with a gain of say 16 (11dBi) and end up with an ERP of 480mW. So ultimatly it's up to the user to ensure they operate the equipment within the terms of the class licence. 
Anyway with the PCM350, I'm note sure that the value of the antenna gain is - I could assume 2.2dBi as for the rubber duck supplied with the PCI cards.
This would mean limiting them to 50mW, gives an ERP that is limited to 82mW, and that if one were to allow 100mW then the ERP would be 166mW.
However that is ignoring the duty cycle portion of the calculation.
If my understanding of this is correct, then this will always tend to increase the EIRP. Huh?
OK - that seems weird to my poor brain. The less time within a given period for which you're tranmitting, the greater your EIRP is considered to be?
on for only half of a given duty cycle means you've got double the transmit power?
So have I gone astray in any of the above?
 Well actually, if I renewed my amateur licence, I have access to the same band range (communicating with other amateurs) at a power limit of 400W. That's 400W of power, not 400W of ERP or EIRP. As much antenna gain as I can throw at it allowed! Mind, getting a linear amp to give 400W of transmit power for that frequency range would be a challenge. _______________________________________________ Aironet mailing list - Aironetcsl.cse.ucsc.edu http://csl.cse.ucsc.edu/mailman/listinfo/aironet