hi guys
i got an issue.
i want to make a wireless link in ideal scenario. no objects in the middle and no interference.Like the perfect scenario.


i have been looking for hours how to calculate all the things i need i have nt found an answer that i can fully understand.

let's say i got two towers of 20 metters height (65 feet)
5 miles apart from each other or 8km
lets use mikrotik board + mini pci express wifi+ ping tails+some antena. (it can be 2,4 or 5,8ghz)

what formula should i use to know how many mW do i need in the card?
what formula should i use to know how long the pigtail might be or how long? cabling loss
what formula should i use to know how many dbi the antena has to be?


-L = C + 20 * log(D) + 20 * log(F)


Distance Loss at F=
in miles in km 900 MHz 2.4GHz 5.8GHz
1.6 mi 2.5 km 99 dB 108 dB 116 dB
3.1 mi 5 km 106 dB 114 dB 122 dB
5 mi 8 km 110 dB 118 dB 126 dB
6.2 mi 10 km 112 dB 120 dB 128 dB
10 mi 16 km 116 dB 124 dB 132 dB



http://www.cisco.com/en/US/tech/tk722/tk809/technologie...
http://www.afar.net/tutorials/how-far/


http://diydrones.com/forum/topics/question-on-frequency...


The free space loss can be calculated according to the formula

-L = C + 20 * log(D) + 20 * log(F)
where D is the distance, and F is the frequency in MHz. The constant C is 36.6 if D is measured in miles, and 32.5 if D is in kilometers. The following are some examples of free space losses:
Distance Loss at F=
in miles in km 900 MHz 2.4GHz 5.8GHz
1.6 mi 2.5 km 99 dB 108 dB 116 dB
3.1 mi 5 km 106 dB 114 dB 122 dB
5 mi 8 km 110 dB 118 dB 126 dB
6.2 mi 10 km 112 dB 120 dB 128 dB
10 mi 16 km 116 dB 124 dB 132 dB

These figures do not take into account deterioration due to weather. Typically, we recommend allowing 15 dB of "fade margin" to accommodate for weather, antenna alignment, and other miscellaneous losses.


thank you in advance.
pd: i know many ppl might try by learning by doing but i like to know in paper before doing purchase.

forget the formulae for now.

For 5500Mhz use path loss for 1km = 106dB.

That is the only number you need to know. The rest is simple. The formulae is a square law, so:

each time you double the distance at another 6dB of loss.

To calculate your setup. Add all the components in "system gain" (including the negative figures.

YOU CAN ONLY ADD 1 RADIO CARD.

so:

Antenna 1 = 24dB
Antenna 2 = 30dB
The transmitting end radio card = 24dBm

Total system gain = 78dB

Now add that to the negative figure of loss (eg 1km = -106dB)

The answer is -28dB.. The radio signal will be roughly -28dB

If you want the figure for 2km, simply add another 6dB loss ( now -34dB)

So for 32kM, the original "constant" has been doubled 5 times... So add another -30dB loss and now the figure is -58dB.

Its much easier to just use the 1kM example above.. Its accurate enough for most applications (assuming line of sight), then just adjust it accordingly.. Dont worry if the distance you want is not 2,4,8,16,32 etc etc, you will soon realise that if your distance is say around 24km, then the figure you will be looking for will be somewhere between 16kM and 32kM value (around 3dB more loss than the value for 16kM)

We should all be working with objectives + a 10dB margin to cover fading or scattering, so an approximation within a dB or so is fine.

Saves pulling your hair out.!!