Re: Sveasoft on WRT54GS continued

Well the math is "pretty" straight forward. The FCC allow you to put 1W 
(1000mW = 30db) into a 6db antenna for a max radiated power of 4W (36db) 
on either end of a P2MP circuit.

You are allowed to subtract cable & connector losses between the final 
rf ampand antenna input & compensate for this difference with a higher 
gain antenna. For simplicity, I will ignore any losses from here on & 
assume that the rf amp is directly connected to the antenna.

For EVERY 1db of antenna gain ABOVE 6db, you must reduce the final rf 
output power by 3db on a P2MP circuit. You may NEVER exceed 4W (36db) 
erp on either end of a P2MP circuit per the FCC.

P2P circuits are different.....Just looked I don't have them on this 
computer, I'll get them for you later & post them.

dbm = 10*LOG(mW) so 64 mW = 18.1 dbm, 48 mW = 16.8, 84 mW = 19.2 dbm.
So the MAX antenna gain you can use is 36-18.1=17.9db, 36-16.8=19.2db, 
36-19.2=16.8db.

Now one last thing, antennas are typically listed in dbi, you should 
calculate using dbd to get ERP otherwise you will get EIRP. Since dbd is 
2.2dbm lower than dbi you can add 2.2 to the above antenna gain to get 
the correct ERP, so you final antenna gains may be 20.1dbd, 21.4dbd, and 
19dbd respectively.

It is not hard to figure setup spreadsheet to do the math for you. 
Calculating Fade Margins (otherwise known as System Operating Margin) is 
more difficult.

You next question, since we are talking about higher gain antennas, 
should be(if you don't already know) "How does the HalfPower BeamWidth 
affect the circuit?"......

Bryan

[email protected] wrote:

> crispin <[email protected] <mailto:crispin%40hotpop.com>> was nice 
> enough to respond to my Sveasoft on WRT54GS Tx power inquiry.
>  
> Yes, I'm trying to cover a wide area using a WRT54GS as a WiFi router 
> and a series of WAP45G's as repeaters. To begin with I used WSB24 amps 
> to boost the power along with the 7dBi antennas. After researching the 
> alternate firmware out there I switched to Sveasoft's to boost the 
> power. And yes, I dropped the WSB24 when I did.
>  
> What I'm unclear about is the math needed to figure out the Tx power + 
> antenna stuff. No, I *don't* want to violate the FCC power ratings. I 
> know that FCC permits for manufacturers are very picky about what is 
> allowed. Like the WSB24 being for the WAP11 et al, not the WRT54GS or 
> WAP54G etc. But I'm assuming that since Linksys open sourced the 
> firmware source code that using a modified router/access point is 
> (somewhat) legal. Or at least *can* be legal. That's the sweet spot 
> I'm looking for.
>  
> BTW, I've boosted my WRT54GS's to only 48mW awaiting info to the 
> contrary.  What oh what is that magic number? Or better yet the math 
> needed to figure it out for myself.
>  
> On a slightly related topic, when Sveasoft lets one specifiy one 
> antenna for transmit and the other for receive, which is the right 
> antenna when facing the front of the box?
>  
> thanks,
>  
>  
> Jerry
> JetCityOrange
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Dev mailing list
>[email protected]
>http://seattlewireless.net/mailman/listinfo/dev
>  
>

_______________________________________________
Dev mailing list
[email protected]
http://seattlewireless.net/mailman/listinfo/dev