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Re: [Openbts-discuss] USRP/OpenBTS Extending Range/Coverage Help
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From: Ralph A. S. d. <ra...@sc...> - 2013-07-23 10:28:16
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Believe me, this crosstalk problem is nothing but a rumor from someone who did not understand the difference between crosstalk when using one frequency vs. using two frequencies. In fact I cover 200 m with a standard WBX and two directly attached small antennae without any problems when using GSM1800 with its large uplink/downlink spacing. At a demonstration a few weeks ago it was no problem to cover three floors of a conference center with only a few mW of output power.
The OP must have some error in his setup, maybe mixing up downlink/uplink or input/output. Or some bad cable, bent connector pin, whatever.
Ralph.
From: Kurtis Heimerl [mailto:khe...@cs...]
Sent: Monday, July 22, 2013 6:52 PM
To: Derek Wells
Cc: ope...@li...
Subject: Re: [Openbts-discuss] USRP/OpenBTS Extending Range/Coverage Help
Oh this is one daughterboard? My understanding is that there's a lot of crosstalk on the board with one daughterboard, that's going to limit your coverage a lot. Also may explain why the duplexer does so little.
On Mon, Jul 22, 2013 at 9:49 AM, Derek Wells <der...@gm...> wrote:
John,
Can you discern whether you are uplink or downlink limited?
That is, is your range limitation due to a transmitter problem or a receiver problem? And furthermore, is it the on phone end (unlikely) or the USRP end of the up or downlink?
It sound like you are working off of one daughterboard, is that correct?
-99 dBm sounds pretty low at 15 meters with a Yagi (like Kurtis said). Consider using the "noise" and "power" commands from the CLI and providing some numbers back to the forum.
And because I've done it before with other systems...check each RF connection and cable to make sure you have a male pin mated with a female socket at every connection, and not two female sockets...it happens.
Derek
On Sat, Jul 20, 2013 at 1:37 AM, Kurtis Heimerl <khe...@cs...> wrote:
There's something wrong with your USRP, you should certainly get more than 15 meters with a USRP1 and a 12db Yagi.
On Sat, Jul 20, 2013 at 1:20 PM, john wake <dag...@ho...> wrote:
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
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