HOW TO INTERACT WITH FSL EQUATION

[Guest]

Archived from groups: alt.internet.wireless (More info?)

Hi folks,

Sorry for this basic question, I have no experience with wireless
issues, but I am learning and trying to understand the theory of
antennas:

My question is what is the FSL really means?

I cam to know that FSL = 36.6 + 20 LOG F + 20 LOG D

For 5.8 GHZ and 14 miles this would yield a 133.86 db, now is this
133.86 is attenuation? Is it related to the receiver sensitivity at the
destination? How can I use this number?



Let me think loud, I understand it this way

If I have EIRP of 36 dB in the transmission end, then this 36 db will
be subtracted from the 133.86, hence I will get a -97.86 db, so my
receiver should be sensitive enough to receive a power of 1.99 e-10
Watts.

Thanks,
ConceptZone

 

[Guest]

Archived from groups: alt.internet.wireless (More info?)

On 29 Aug 2005 04:05:27 -0700, "ConceptZone" <ismail@conceptzone.net>
wrote:


>Sorry for this basic question, I have no experience with wireless
>issues, but I am learning and trying to understand the theory of
>antennas:
>
>My question is what is the FSL really means?

Free Space Loss. It's really a measure of inverse square law. Double
the distance and you loose 4 times (-6dB) the power. I don't wanna go
into the field equations, but double the frequency and you also lose 4
times the power. See the bottom half of:
> http://www.softwright.com/faq/engineering/Free%20Space%20Field%20and%20Loss%20Calculations.html
for the derivation.

>I cam to know that FSL = 36.6 + 20 LOG F + 20 LOG D

Yep, where FSL is in dB, F is in Mhz, and D is in miles.

>For 5.8 GHZ and 14 miles this would yield a 133.86 db, now is this
>133.86 is attenuation?

Yes.

>Is it related to the receiver sensitivity at the
>destination?

No. See below.

>How can I use this number?

The purpose of doing everything in dB is to allow simple addition and
subtraction to be used for calculations. Gain is added. Loss is
subtracted. You start at the transmitter that put's out XX dBm of
power (decibels above 1 milliwatt). The coax cable loss is
subtracted. The tx antenna gain is added. The free space loss is
subtracted. The receive antenna gain is added. The receive coax loss
is subtracted. The difference between the receiver sensitivity and
what's left of the signal is the fade margin or operating margin.
See:
> http://groups.google.com/group/alt.internet.wireless/msg/c514c4b9092cc9e2
for an example of how to use the numbers. Well, convert the 2.5 miles
to FSL in dB and everything should add up.

>Let me think loud, I understand it this way
>
>If I have EIRP of 36 dB in the transmission end, then this 36 db will
>be subtracted from the 133.86, hence I will get a -97.86 db, so my
>receiver should be sensitive enough to receive a power of 1.99 e-10
>Watts.

Sorta. You're ignoring the receive antenna gain and the coax and
connector losses. The -98dB (watch your significant figures) is the
power that the receive *ANTENNA* gets, not what the receiver input
gets.

>Thanks,
>ConceptZone


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
AE6KS 831-336-2558

 

[Guest]

Archived from groups: alt.internet.wireless (More info?)

Really Thank you so much on such a valuable information