# Lost between three woods

#### Janis59

Joined Aug 21, 2017
1,855
One guy asked an advice for his poor minus minus GSM coverage. I gave the councel to buy the https://www.ebay.com/itm/1955217324...rUT92Aw8NkPMcRTDVjJHtMOcqizQ4_b98aWLIR5f2RjlA

And then I started to calculate and probably got a swine in the sack. So, the input data: Max Gain 72 dB (producer given); 5 dB Nyquist Noise Figure (producer given). In the first approximation, signal is diminishing proportionally to distance in square. Thus, if the good phone have weak but still satisfactory signal at -120 dBm (phone maker given) and absolute unsatisfactory at -127...-130 dBm (phone maker given), then 72 dB=60+6+6=100x2x2=4000x or sqrt(4000)=60x. What?! Distance have 60-folded?? Never! Dont believe in no way.

Okay, probably there is poridge between voltage decibels and power decibels. Therefore shall take the screen calulator from www.rfwireless-world.com/calculators/Antenna-Range-Calculator.html. Shall put-in that <antenna amplification factor> 72 dB, the <transmitter power> +33 dB for 800 MHz or (better) +30 dB for 1800 MHz and get... 1.5 million kilometers. Nonsens!!!

Okay, bit validate. Antenna sensitivity 0.5 dB, 30 dBm transmitter and get 420 km by rfwireless. Never!!!. Okay, sometimes GSM transmitters have rather small power like +8 dBm or even +4 dBm only. Am not sure what is the typical power at our towers, but let take the least, 4 dBm, and then distance is ... 21 km. What the f..... Nothing works like it should. What the mistake I am getting into having so absurd output??

Second question - what means practically the 5 dB Noise figure? Should it be added to input dBm or to output dBm? Anyway, my marine radiostation hace 0.15 dB Noise factor thus I guess the 5 dB is rather much. However for transistor indeed 5 dB is rather reasonable figure. So, how I may decide from this Noise figure the distance after what no signal will be received in-spite it exist in the air?

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#### Ya’akov

Joined Jan 27, 2019
9,237
Where are you getting your numbers?

The "gain" of 72dB apparently means a maximum output of 23dB, it isn't the gain figure for the antenna. I am having a hard time following your numbers in general.

#### Janis59

Joined Aug 21, 2017
1,855
The 72 dB amplification factor is one of producer advertised basic parameters given in first of two references I pousted.
If the antenna with 0 dB is amplificated by 72 dB then it is 72 dB equivalent antenna. Thus, I believe, there is no any difference to plug-in such imaginative superantenna or plug the <normal> weak antenna through the amplifier. And yes, of course there stand inside the authomatic amplification gain limiter. If the output signal is too large, it diminish the Amplifier Gain.
Data of GSM station typical power is taken from it standard.
About 23 dB.... Its not specified by producer, do the 72 dB is power amplification gain or voltage amplification gain.
Data of mob.tel. sensitivity is brought from my phone installed software (very useful) NetworkCellInfoLite. Normally I have about -105, sometimes -115, very rarely -120 dBm.
The aim is to evaluate the theoretical max distance from tower in <with amplifier> into comparizon <with no-amplifier>.

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