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# Range calculation and comparison with the reality

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#### KC_O_o

##### Junior Member level 1
From Friis equation, 6 dB increased in TX power, range would also be double.
Does anyone perform some range comparison in real situation?

Or more specifically, class 3 Bluetooth tx at 0dBm can guarantee 10m range. So 6 dBm would be 20m? 12dB correspond to 40m? 18 dB (closed to class 1) correspond to 80m? Can I say that?

Thanks

Re: Range calculation

Your calculations are free space. In the real world there are reflections that produce multipath interference and Fresnel zone attenuation. There are also obstructions.

For the shorter paths these are less troublesome.

There is also co-channel and adjacent-channel interference that will reduce your range.

Re: Range calculation

You can measure it now with

Re: Range calculation

flatulent said:
Your calculations are free space. In the real world there are reflections that produce multipath interference and Fresnel zone attenuation. There are also obstructions.

For the shorter paths these are less troublesome.

There is also co-channel and adjacent-channel interference that will reduce your range.

For calculate covering wide urban area (outside house or low attenuate walls in house), most common using model is 'Okamura-Hata' and coarse descriptions calculate a 12 dB attenuation per double distance (for example UMTS) and from my experience for 900 and 1800 MHz is very close to real world measure.

House is very tricky to predict depend of build materials, and special if wall build on materia with much bound water (gips, CaSO4 + 2 * H2O, i not know name in english, guess gypsum) and board of this is very common to build walls for rooms inside house in sweden, and seem very hard for frequency above 2 GHz to passed...

For example UMTS drops very fast inside house (in sweden) and more or less useless few meter behind wall in house if not have a UMTS base station very, very close.... or big windows without metallic heat reflection layer...

you can have -55 dBm UMTS outside windows, but <3 m inside, signal goes under -90 dBm and I sense surrounding gypsym walls suck down (absorbed) all > 2 GHz in rooms like cold black body chamber, even if not passed walls - i'm unbelive this first time i see this situation...

same situation for bluetoth and Wlan, and have hard to cover more than closest rooms , but unwanted, same signal can going very wide distanse outside house passed trougth windows...

GSM 900 and 1800 have not trouble in same house and I cannot understud how few 100 MHz higher frequency above GSM 1800 can give so much more covering trouble...

gheeees.... not easy to predict...

Re: Range calculation

Hi all,

What if we assum the range test is to be performed on a open site with only a concrete floor.
In that case, I do agree using a 2 way model, in which only the line of sight path and the ground reflected wave are considered, then 12 dB half distance might be true.
But does anyone has idea on how effective a concrete floor would reflect or absorb the signal at 1.8G or 2.4G? What kind of test should be done to compare different materials in this scenario?

Thx a lot!

Re: Range calculation

The concrete floor is a dielectric that is generally similar to that used in capacitors so the dielectric constant is way above 1. This will make most of the waves reflect and a little absorbed.

Re: Range calculation

My post two above is in error. I have just seen a graph of reflection coefficient for concrete. It depends on polarization and angle and averages 0.3. This is probably the basis for the rule of thumb in radio path predictions that there is a 10 dB loss when reflecting off of a building.

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