[Openbts-discuss] USRP/OpenBTS Extending Range/Coverage Help

[john w. <dag...@ho...>]

Hello guys,

We are  having trouble extending the range of our USRP1 which is running OpenBTS I really hope someone can help our current setup is as follows

RX = Antenna -> Duplexer -> LNA -> USRP 
TX = Same antenna -> Same duplexer -> Power Amplifier -> Fullband Transmit Filter -> USRP

When we try running the USRP with just the antenna we get a range of around max 10-15 meters the phone showing -99dBM when we add the power amp the range increases by a few meters however when we also add the LNA so we have both the LNA + power amp connected at the same time 
this is when the range decreases to around 5 meters.

We would be happy if we were able to cover 1/2 mile or anything near this range we do have a temporary license to transmit in our frequency however this expires in 2 months. 

There has been quite a bit spent on equipment so far trying to extend the range  with no luck it seems the USRP is made only to work at a very short range so any help on how to do this would be very much appreciated.

Also would adding a bandpass filter to the RX side make any difference?

The spec of equipment we are using is as follows

900 Mhz 12 dBi Yagi antenna

Frequency（MHz）824~960MHz
Length:55cm
SWR ≤≤1.5
Input Impedance-Ω: 50
Horizontal Beamwidth -° :54/48/40/36/30
Vertical Beamwidth -° :48/40/36/32/30
Maximum Power -W :100
Bandwidth-MHz :154/154/154/140/120

Duplexer

30 W GSM Duplexer       TX             RX
Pass Band             925 - 960 MHz     880 - 915 MHz
Insertion Loss     1.0 dB     1.0 dB
Passband Ripple     0.2 dB             0.2 dB
Rejection     50 dB @ 80-850 MHz      50 dB @ 80-800 MHz
                50 dB @ 1-3 GHz     50dB @ 1-3 GHz
Return Loss     minimum 20 dB
Impedance     50 Ohms
Coupling Port     -30 dB (+/- 1.5 dB)
Power             30 W average RF poewr


LNA

Parameter Unit Minimum Typical Maximum 
Frequency Range MHz 850 950 
Small Signal Gain dB 40 41 
Output Power Pout @ Pin = 0dBm dBm +40 
Saturated Power Psat @ Pin = +5dBm dBm +42 
IP3 dBm +50 
Reverse Isolation dB -75 
Efficiency at Pout = +40dBm % 38 
VSWR Input 1.4:1 
DC Power Supply V +12 

Power Amp

775-950 Mhz
40 dB gain 
+18 dBm

Filter

Passband: 925-960 MHz
Passband Insertion Loss: 1.5 dB maximum
Rejection:
DC-915 MHz 80 dB minimum
1000-2880 MHz 60 dB minimum
Passband Return Loss: 15 dB minimum
Maximum Power Handling:
CW 10 watts
Peak Instantaneous 40 watts
Intermodulation Products: -110 dBm maximum
with two +34 dBm carriers