From: Nor G. <no...@gm...> - 2010-02-26 17:08:43
|
Hi I've been playing with OpenBTS for a few weeks now and would like to share some experiences with the list. Clocking I first tried using the USRP 64 MHz clock. It was far off and none of my phones found the signal. Purchased a 13 Mhz TCXO on ebay and soldered it to a 4x clock multiplier from TI (free sample). Works perfectly. Tx/Rx isolation I'm using a single RFX900. After I removed C202 the isolation was app. 50 dB and it was possible to send to and receive from a phone anywhere in the same room. I then grounded pin 8 on U209 and that raised the isolation to 65 dB. That made it possible to take the phone to the next room. I wanted more isolation and tried shielding the TX amplifer. Took me a whole day to make and solder a box around the tx amplifers, but the improvement was only 2 - 3 dB. At this point I actually considered cutting the RFX900 in two to separate the transmitter and receiver, but I had one more idea first. I completely removed the trace from U209 pin 3 to C205 and soldered a new SMA connector to the board, placed directly above C205 with the center pin soldered to C205. This seems to have (I'm not able to measure accurately) increased the isolation to 90 dB. Rx gain Even with the improved isolation, it was still not possible to setup a call from outside the house. To avoid receiver saturation because of tx leaking into rx, I had to reduce the rx gain from 80 dB to 30 dB. To compensate for the loss of sensitivity, a 40 dB amplifer (Lucent KS21583 L9, $20 on ebay) was connected outside the USRP. I now have a good balance between up-/down-link range, and are able to setup a call when the Nokia Field Test Display indicates a signal strength of -100 dBm. With a small whip antenna on the BTS that is 1/2 mile away. With a decent antenna it would be a lot more. Duplexer I'm using a "G-way Microwave Diplexer P/N CD940/6SK-E" (I know a diplexer is supposed to be different from a duplexer, but it works fine, so I don't care). It has 6 cavities on each side and provides more isolation than I can measure. This was also $20 on ebay. Nor |
From: Jakub <46...@wp...> - 2010-03-01 08:12:09
|
<div> </div> <div>Hello</div> <div>Good qality for long distance operation (more than 50m) is using two</div> <div>SAW dplexers dismounted from Nokia 3310. This duplexer are two bands 900/1800-RX/TX and can handle 1W of rf power.</div> <div>Duplexers can be used as a filters when connected 50R SMD resistors to unused ports</div> <div>With this duplexer connected between rx ends and external receive TMA with good calculated</div> <div>gain results will be reale good (using duplexers as a filters is needed for using separeted antenna</div> <div>for rx and tx).</div> <div>The second improvement is using good rf isolation at powering rx and tx part of transceiver and good shielding this parts.</div> <div>At the TX ends good effects is achived by connecting this saw filter and adding MMIC power amplifier, especcialy good effects is with BGY916/5 or BGY2016 16W power amplifiers.</div><br /> |
From: Alexander C. <ale...@gm...> - 2010-03-01 10:34:33
|
Hi Jakub, All, Jakub -- Great to hear your results! Could you place your results on the wiki too, please? If you have any pictures about your setup and picture which shows where duplexer is located in 3310, it would be great if you upload them to the wiki too. Then others can reproduce your results more easily. If you have more information about the quality of such solution then just ">50m" it would be nice to hear about it too! All -- In general, please consider adding copying information from your mails to the wiki if you post useful information from which others may benefit, such as ways to modify USRP for longer ranges. It will be a good donation to the project, as documentation is always too sparse in open-source projects. And this way we will grow our documentation base constantly. PS Does 3310 really have duplexer? I always thought that most handsets just re-tune their rx/tx on every frame or use switches, but do not use duplexers. 2010/3/1 Jakub <46...@wp...>: > Good qality for long distance operation (more than 50m) is using two > SAW dplexers dismounted from Nokia 3310. This duplexer are two bands > 900/1800-RX/TX and can handle 1W of rf power. > Duplexers can be used as a filters when connected 50R SMD resistors to > unused ports > With this duplexer connected between rx ends and external receive TMA with > good calculated > gain results will be reale good (using duplexers as a filters is needed for > using separeted antenna > for rx and tx). > The second improvement is using good rf isolation at powering rx and tx part > of transceiver and good shielding this parts. > At the TX ends good effects is achived by connecting this saw filter and > adding MMIC power amplifier, especcialy good effects is with BGY916/5 or > BGY2016 16W power amplifiers. > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > Openbts-discuss mailing list > Ope...@li... > https://lists.sourceforge.net/lists/listinfo/openbts-discuss > > -- Regards, Alexander Chemeris. |
From: Matt E. <ma...@et...> - 2010-02-26 18:00:06
|
On 02/26/2010 09:08 AM, Nor Gsm wrote: > Hi > I've been playing with OpenBTS for a few weeks now and would like to > share some experiences with the list. > Clocking > I first tried using the USRP 64 MHz clock. It was far off and none of my > phones found the signal. Purchased a 13 Mhz TCXO on ebay and soldered it > to a 4x clock multiplier from TI (free sample). Works perfectly. > Tx/Rx isolation > I'm using a single RFX900. After I removed C202 the isolation was app. > 50 dB and it was possible to send to and receive from a phone anywhere > in the same room. I then grounded pin 8 on U209 and that raised the > isolation to 65 dB. That made it possible to take the phone to the next > room. I wanted more isolation and tried shielding the TX amplifer. Took > me a whole day to make and solder a box around the tx amplifers, but the > improvement was only 2 - 3 dB. At this point I actually considered > cutting the RFX900 in two to separate the transmitter and receiver, but > I had one more idea first. I completely removed the trace from U209 pin > 3 to C205 and soldered a new SMA connector to the board, placed directly > above C205 with the center pin soldered to C205. This seems to have (I'm > not able to measure accurately) increased the isolation to 90 dB. Thank you for doing this investigation. I had not thought of grounding that pin and it looks like it gives a very easy 15 dB improvement. I'm glad you are able to get 90 dB by completely bypassing the antenna switch. Any antenna switch is going to have some leakage, and that is always going to be the dominant source. > Rx gain > Even with the improved isolation, it was still not possible to setup a > call from outside the house. To avoid receiver saturation because of tx > leaking into rx, I had to reduce the rx gain from 80 dB to 30 dB. To > compensate for the loss of sensitivity, a 40 dB amplifer (Lucent KS21583 > L9, $20 on ebay) was connected outside the USRP. I now have a good > balance between up-/down-link range, and are able to setup a call when > the Nokia Field Test Display indicates a signal strength of -100 dBm. > With a small whip antenna on the BTS that is 1/2 mile away. With a > decent antenna it would be a lot more. This is also a great data point. I have been saying for some time that 80 dB of gain is WAY too much. It will cause even relatively weak signals to saturate and make you more susceptible to blocking from other phones and even other base stations. Noise figure stops improving long before you get to 80, so there is little to be gained by having such a high gain. As you have found, 30 works well if you have an LNA in front. If you don't, then something in the 45 to 55 range is probably optimal. Thanks for being so thorough in your analysis and for reporting your findings to all. Matt |
From: Harvind S. <hs...@ke...> - 2010-02-26 20:13:31
|
Nor, Thanks for the experiment results! We've found that an external LNA of 30dB with a USRP gain of 30-40dB to be about ideal. I'll provide some more data as soon as I get more than 100B/s internet connectivity. Also, the Rx gain will be configurable from the command line in an upcoming release. --- Harvind On Fri, 2010-02-26 at 18:08 +0100, Nor Gsm wrote: > Hi > > I've been playing with OpenBTS for a few weeks now and would like to > share some experiences with the list. > > Clocking > I first tried using the USRP 64 MHz clock. It was far off and none of > my phones found the signal. Purchased a 13 Mhz TCXO on ebay and > soldered it to a 4x clock multiplier from TI (free sample). Works > perfectly. > > Tx/Rx isolation > I'm using a single RFX900. After I removed C202 the isolation was app. > 50 dB and it was possible to send to and receive from a phone anywhere > in the same room. I then grounded pin 8 on U209 and that raised the > isolation to 65 dB. That made it possible to take the phone to the > next room. I wanted more isolation and tried shielding the TX > amplifer. Took me a whole day to make and solder a box around the tx > amplifers, but the improvement was only 2 - 3 dB. At this point I > actually considered cutting the RFX900 in two to separate the > transmitter and receiver, but I had one more idea first. I completely > removed the trace from U209 pin 3 to C205 and soldered a new SMA > connector to the board, placed directly above C205 with the center pin > soldered to C205. This seems to have (I'm not able to measure > accurately) increased the isolation to 90 dB. > > Rx gain > Even with the improved isolation, it was still not possible to setup a > call from outside the house. To avoid receiver saturation because of > tx leaking into rx, I had to reduce the rx gain from 80 dB to 30 dB. > To compensate for the loss of sensitivity, a 40 dB amplifer (Lucent > KS21583 L9, $20 on ebay) was connected outside the USRP. I now have a > good balance between up-/down-link range, and are able to setup a call > when the Nokia Field Test Display indicates a signal strength of -100 > dBm. With a small whip antenna on the BTS that is 1/2 mile away. With > a decent antenna it would be a lot more. > > Duplexer > I'm using a "G-way Microwave Diplexer P/N CD940/6SK-E" (I know a > diplexer is supposed to be different from a duplexer, but it works > fine, so I don't care). It has 6 cavities on each side and provides > more isolation than I can measure. This was also $20 on ebay. > > Nor > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ Openbts-discuss mailing list Ope...@li... https://lists.sourceforge.net/lists/listinfo/openbts-discuss |
From: Alexander C. <ale...@gm...> - 2010-02-26 21:08:08
|
Hi Nor, Great results! Could you post your results to an appropriate wiki pages, please? This should help others to find this information more easily. I think it's a good time for someone to clean up one-RFX patch to make it possible choose boards configuration from the config file. Then it should be possible to include it into mainline after David's approval. -- Regards, Alexander Chemeris. |
From: Sylvain M. <24...@gm...> - 2010-02-26 21:08:22
|
Nor, Yes thanks a lot :) I'm working on a RF front end for openbts so that's precious info :) First, I'm a little surprised that moving the RX2 SMA before the antenna is such a gain. After all, once C202 is removed and the pin grounded, there is no more connection to the TX side through there. What am I missing ? Second, when looking at the figures choosing a LNA, we noticed that we couldn't put a very strong one if we didn't want to saturate the input stage for close phones (think more picocell where the bts can be only a couple meters from the antenna). My reasoning was such : - Phone TX power is regulated but the lowest then can transmit at is 0 dBm on a 0 dB gain antenna - Traveling trough 1 m of air: about 40 dB loss - Simple RX antenna 3 dB gain - Duplexer insertion loss 3 dB - Our external LNA : x dB gain - Our external RX filter insertion loss : 3.5 dB - The RFX LNA MGA82563: 13.5 dB - Maximum input level at the AD8347 (when set at minimum gain) : - 2 dBm So : -2 dBm = 0 dBm + 0 dB - 40 dB + 3 dB - 3 dB + x dB - 3.5 dB + 13.5 dB => x = 28 dB absolute max for the LNA (after that -> saturation in the mixer) And that's without much safety margin. In the end, we chose a 15 dB LNA because there wasn't one ~ 25 (only single stage 15-16 or double stage 31-33 ...). Do you see anything wrong with my math here ? Cheers, Sylvain |
From: Nor G. <no...@gm...> - 2010-02-27 16:25:12
|
2010/2/26 Sylvain Munaut <24...@gm...> > Nor, > > Yes thanks a lot :) I'm working on a RF front end for openbts so > that's precious info :) > > First, I'm a little surprised that moving the RX2 SMA before the > antenna is such a gain. After all, once C202 is removed and the pin > grounded, there is no more connection to the TX side through there. > What am I missing ? > My best guess is that the signal leaks through the common power supply. > Second, when looking at the figures choosing a LNA, we noticed that we > couldn't put a very strong one if we didn't want to saturate the input > stage for close phones (think more picocell where the bts can be only > a couple meters from the antenna). My reasoning was such : > > - Phone TX power is regulated but the lowest then can transmit at is > 0 dBm on a 0 dB gain antenna > - Traveling trough 1 m of air: about 40 dB loss > - Simple RX antenna 3 dB gain > - Duplexer insertion loss 3 dB > - Our external LNA : x dB gain > - Our external RX filter insertion loss : 3.5 dB > - The RFX LNA MGA82563: 13.5 dB > - Maximum input level at the AD8347 (when set at minimum gain) : - 2 dBm > > So : > > -2 dBm = 0 dBm + 0 dB - 40 dB + 3 dB - 3 dB + x dB - 3.5 dB + 13.5 dB > => x = 28 dB absolute max for the LNA (after that -> saturation in the > mixer) > > And that's without much safety margin. > In the end, we chose a 15 dB LNA because there wasn't one ~ 25 (only > single stage 15-16 or double stage 31-33 ...). > > Do you see anything wrong with my math here ? > No. 15 dB sounds like a good choise for close range operation. And, provided you have the required tx/rx isolation (two RFX cards), you can easily reconfigure for wide area coverage by turning up the AD8347 gain. My reasons for using the 40 dB amp were: 1. It was the only amplifier I had available 2. I was aiming for long range and did not worry about phones close to the antenna 3. The system was limited by the 90 dB tx/rx isolation BTW: What is the effective tx/rx isolation when using two transceiver boards? Nor |
From: <ope...@ol...> - 2010-03-09 21:44:08
|
Hi all, On Sat, 2010-02-27 at 17:25 +0100, Nor Gsm wrote: > 2010/2/26 Sylvain Munaut <24...@gm...> > Nor, > > Yes thanks a lot :) I'm working on a RF front end for openbts > so > that's precious info :) > > First, I'm a little surprised that moving the RX2 SMA before > the > antenna is such a gain. After all, once C202 is removed and > the pin > grounded, there is no more connection to the TX side through > there. > What am I missing ? > My best guess is that the signal leaks through the common power > supply. > > Second, when looking at the figures choosing a LNA, we noticed > that we > couldn't put a very strong one if we didn't want to saturate > the input > stage for close phones (think more picocell where the bts can > be only > a couple meters from the antenna). My reasoning was such : > > - Phone TX power is regulated but the lowest then can > transmit at is > 0 dBm on a 0 dB gain antenna > - Traveling trough 1 m of air: about 40 dB loss > - Simple RX antenna 3 dB gain > - Duplexer insertion loss 3 dB > - Our external LNA : x dB gain > - Our external RX filter insertion loss : 3.5 dB > - The RFX LNA MGA82563: 13.5 dB > - Maximum input level at the AD8347 (when set at minimum > gain) : - 2 dBm > > So : > > -2 dBm = 0 dBm + 0 dB - 40 dB + 3 dB - 3 dB + x dB - 3.5 dB + > 13.5 dB > => x = 28 dB absolute max for the LNA (after that -> > saturation in the mixer) > > And that's without much safety margin. > In the end, we chose a 15 dB LNA because there wasn't one ~ 25 > (only > single stage 15-16 or double stage 31-33 ...). > > Do you see anything wrong with my math here ? > No. 15 dB sounds like a good choise for close range operation. And, > provided you have the required tx/rx isolation (two RFX cards), you > can easily reconfigure for wide area coverage by turning up the AD8347 > gain. > I am working with Sylvain on the RF front. Apart from the duplexer and LNA there will be place for one or two saw-filters on the USRP RX input side. Our calculations show that one saw filter should be sufficient, but just in case we put room for a second one. Did any of you experiment or do measurements with saw filters on the USRP RX input. Best Regards, Martin Dudok van Heel > |