[MLB-WIRELESS] New submission up at Inquiry

[Steven Haigh]

Curious as to how you got these figures.... see below...

On Thu, 20 Jun 2002 08:42, evilbunny wrote:
> Hello Ben,
>
> Quick math lesson...
>
> 15dBm - 2dBm + 13dBi + 14dBi - 2dBm = 38dBm

Now, +36dbm is the maximum EIRP limit of 4W......
+15dbm = transmit power
          = 30mW

-2dbm = cable loss
          = ~ -1mW (0dbm = 1mW, 10dbm = 10mW, 20dbm = 100mW)

+13dbi = antenna gain (is it me or shouldn't you mix dBi with dBm?)
          = 29mW * 13

Anyhow, going from your figures, +15 - 2 + 13 = 26dBm

Now with 1W EIRP = 30 dbm, and 100mW being 20dbm, being a logarithmic 
calculation, (and I'm not going to work it our perfectly :) then 26dbm would 
be roughly 600mW output EIRP on the TX side. now a 13db antenna is either a 
wide directional or a patch antenna... only losing 2db in cable means a very 
short run of cable and excellent connectors (usally expect about 0.5db 
insertion loss per connector)... So in this case, 1db loss from cable, and 
1db loss on connectors...

Where does this other +14dbi and cable loss come from? I'm assuming you're 
also including the recieve gain of an antenna and cable loss?

>
> free space loss over 30km = 130dBm
>
> 38 - 130dBm = -91dBm... ie still able to get a connection on cisco and
> lucent based gear... and guys in WA have made claims of such... I
> personally have done 10km on less then 1/2W at both ends... any
> further I would need a boat...

This I can't fully remember enough to comment on... but IIRC you don't include 
the recieve gain in the free space loss? can't remember exactly, I could be 
wrong...

-- 
Signed,
Steven Haigh
President - Melbourne Wireless
www.wireless.org.au


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