[Discuss-gnuradio] Limited Rx BW on XCVR2450 daugtherboard

[Stephen Lai]

Hi All,

I've been having problems sending a 25 Msym/s BPSK stream between two USRP2's with XCVR2450 daughterboards.  I've tracked it down to the Rx circuitry limiting the passband to ~14 MHz when at least 20 MHz should be available.

Sifting through the db_xcvr2450.c/db_xcvr2450.cc files, I think there may be a bug which causes the baseband LPF in the MAX2829 device to cutoff at 7.5 MHz instead of 9.5 MHz when the board is configured for Rx.

Referring to "LPF Register" on the MAX2829 datasheet, the old code...

static void
set_reg_lpf(struct db_xcvr2450_dummy *db){
  int reg_lpf = (
    (db->common->d_rssi_hbw<<15)  |
    (db->common->d_txlpf_bw<<10)  |
    (db->common->d_rxlpf_bw<<9)   |
    (db->common->d_rxlpf_fine<<4) | 7);
  send_reg(reg_lpf);
}

...seems like it should read...

static void
set_reg_lpf(struct db_xcvr2450_dummy *db){
  int reg_lpf = (
    (db->common->d_rssi_hbw<<15)  |
    (db->common->d_txlpf_bw<<9)  |
    (db->common->d_rxlpf_bw<<7)   |
    (db->common->d_rxlpf_fine<<4) | 7);
  send_reg(reg_lpf);
}

...to be set correctly.

Has anybody else had problems with this?  I'm using txrx_edk10.1_r11370.bin.  I don't have Xilinx/EDK tools installed on my setup, but if someone is willing to build a load with the fix, I can test it out.

thanks,
Steve