[MLB-WIRELESS] Wireless Cards

[Robert Foster]

Who can teach me all of this stuff? (and more?)  A curiosity thing more than
anything (I need a hobby) :)

Robert Foster
Mountain Visions P/L
Australia.
rfoster at mountainvisions.com.au


> -----Original Message-----
> From: Richard Nelson [mailto:richard.nelson at eng.monash.edu.au]
> Sent: Tuesday, 23 October 2001 3:21 PM
> To: melbwireless at melbwireless.dyndns.org
> Subject: Re: [MLB-WIRELESS] Wireless Cards
>
>
> Yeah. It's not well understood, but those who know it well can do path
> calculations and tell you in advance whether a link will work well, not
> at all, or overload your receiver.
>
> Drew wrote:
> >
> > it seems there is a lot of conflicting info on this subject
> >
> > i swear i've seen a formula of power * gain = eirp which with a lucent
> > card and 18dbi would give .03 * 18 = .54W EIRP
>
> If you could tell us where you have seen this formula we could have a
> look and see if we can work out what is going on, but I am certain that
> there is something funny because AFAIK you never multiply dB.  The whole
> point of using dB is to enable calculations just by adding.  Remember
> this stuff was all started before the days of electronic calculators.
>
> >
> > then there's matthew's formula which would give .03 * 64 = 1.92W EIRP
> >
> > then there's ydi's formula
> > (http://www.ydi.com/decibels-radio-systems.php) which would give
> > 18dbi + 15dbm = 33dbm = 2W EIRP
>
> This is the result I agree with.
> These two numbers (and formulas) are so close as to be effectively the
> same.  In radio terms you generally round to the nearest dB so results
> are typically accurate to +/- 10% or more.   The ratios that we deal
> with are really large.  If your receiver power is -80dBm then that is a
> one hundred millionth of a milliwatt or a ten billionth of a watt.  When
> you have a ratio of ten billion or so then a mere 10% here or there  is
> nothing really.   This is also why the difference between a 30mW card
> and a 100mW card is much much less than many people realise.  It is all
> in the antenna gain (and cable/connector losses).
> >
> > then there's a pretty confusing one at
> >
> http://www.personaltelco.net/index.cgi/FccRegs?action=highlight&value=eirp
> >
> > aimed at the USA
> >
> > ugh.
> >
> Ugh is right.  That appears to be more to do with FCC regs than actual
> power calculations.
>
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