GSM repeater

For implementing GSM repeater we need 2TX and 2RX. LMS7002M supports 2TX and 2RX. how ever LMS7002M has two PLLs. one TxPLL and other RxPLL. My understanding is both TX have same LO frequency and both RX will have same LO frequency. For implementing GSM repeater we need to connect TXPLL to TX1 and RX2, RXPLL to TX2 and RX1. I would like to understand how it can be achieved.

Can Terasic GX cyclone V starter kit be used with MyriadRF and zipper boards via HMSC ?


yes it can be connected


What is the frequency difference between your GSM bands? LMS7002M has internal NCO which can be used to get frequency separation between LMS7 channels in your application.


Thanks for giving idea of using NCO for achieving frequency separation between TX1 and TX2 as well as RX1 and RX2. separation requirement is 45 MHz for 900 MHz band, 95 MHZ for 1800 MHZ band and 190 MHZ for 2100 MHZ band.


45 MHz Rx path separation per band is doable using NCO solution in LMS7 transceiver. For higher frequency separation you would require to use external mixer connected to receiver/transmitter input/output.


I guess better option is to use two LMS6002D and microprocessor. only trouble is filters are not completely tunable.

I mean for 2G band select filter band width required to define as Number of channels* 200 KHz.

2 x LMS6002D is a better option for your application.

Internal filters have some flexibility for fine tuning. You can use filter calibration registers to adjust filter bandwidth, see [link].


Thanks for providing critical information on fine tuning filter beyond defined steps. This was helpful.

In case of GSM repeater application incoming signal band ( e,g. say 6.2 MHz out of complete GSM band of 900 MHz) needs to filtered and retransmitted again. This means we do not need I and Q. simple down conversion, filtering and up conversion will be ok for this application.

How to implement single line ( with out I and Q ) receiver and Transmitter ?

other option is of filtering required band from I and Q and looping back. will this approach work ?


From hardware point there couple option you can do:

  1. You can use baseband Loopback options. This would loopback received signal to Tx path. But I and Q channels. But you do not need to use internal DAC/ADC.
  2. You can use analog input/outputs and external filer (if needed). In this way you can use only one channel.

But from application point, I think there are some performance requirements and options mentioned above may not be good enough for them to meet.

My safe bet would be to use some baseband such us small and low power FPGA. Do the digital loopback inside, implement necessary DC offset/ IQ imbalance calibration routines and maybe Echo cancellation filter (depends on requirements).


I agree with you. In fact I am looking for some reference design for the same. can you suggest where should I look for more detail.


There are designs made for the GSM application already. You may check Fairwaves guys [link] or Nuand [link].


Thank you for all the useful information provided in this thread.
This link:!msg/limemicro-opensource/jpcR2kmUVoc/CcB1p_O50wMJ

provides information that one cannot use same TX and RX clocks, 1 mhz separation is required.

So i guess building a repeater with LM6002 is not that simple after all?
All additional information is highly appreciated.


Hi Zortz,

In most repeater applications the frequency separation is used.
The offset frequency depends on the application requirement.
Most of them are about 5 MHz separation or 10 MHz, and LMS6002D is capable of doing that.
So the repeater can be easily implemented.

0 MHz or even 1 MHz separation is rear used in repeaters.
What application you want to make? And why do you need 0 MHz separation?

Here you can find more theory on how repeater works:

for wcdma band 70 Mhz IF bandwidth is required. How to achieve that ?

Hello @Ajayp,

Which band you are targeting?
LMS6002D does not support this BW, but LMS7002M can do this BW via the analog IOs.


There is a recent ‘Instructable’ HERE about using the LimeSDR as a repeater although it seems to be incomplete - there’s no mention of how the duplexers were constructed. I’d very much like to complete this project myself!

You tend to just buy duplexers, rather than make them. If you do a search for Band 20 Duplexer it brings up quite a few results.

Yes, I’ve seen some of these components. I was hoping someone was building the whole gadget … obviously not! The components are extremely small ie 2mm SQR … But I guess I’m going to have to bite the bullet and build them myself. All I need now is a LimeSDR board … Are there any spare ones eg shop spoiled / 2nd hand / unwanted Christmas presents? :wink: