DBSRX filter efficiency?

GNU Radio
1

Dear Gnuradio hackers,

I have problems with the DBSRX module of the USRP: I see GSM on all
frequencies. I hope somebody can answer my questions: Is there an
antialiasing filter somewhere in the design? If so, what is its nominal
efficiency? Where can I find data sheets for the MAX211x chips?

Thanks in advance,
Andreas

2

On Mon, May 18, 2009 at 12:08:01PM +0200, Andreas Bogk wrote:

Dear Gnuradio hackers,

I have problems with the DBSRX module of the USRP: I see GSM on all
frequencies. I hope somebody can answer my questions: Is there an
antialiasing filter somewhere in the design? If so, what is its nominal
efficiency? Where can I find data sheets for the MAX211x chips?

Thanks in advance,
Andreas

Hi Andreas! Welcome!

Try turning the Rx gain down.

The datasheets should be on Maxim’s site, though I think they’re
discontinuing the part. If you can’t locate them, let me know and
I’ll see if I can’t find one for you.

Eric

3

Eric B. wrote:

Hi Andreas! Welcome!

Thanks! :slight_smile:

Try turning the Rx gain down.

Been there, done that. It doesn’t get rid of the images.

The datasheets should be on Maxim’s site, though I think they’re
discontinuing the part. If you can’t locate them, let me know and
I’ll see if I can’t find one for you.

I can’t find them, and googling for MAX211x only brings me to Gnuradio
related information. Is there a magic part number I need to know? I’d
appreciate the datasheets, or alternatively the information that the
filters are indeed in the chip and not tunable.

Cheers,
Andreas

4

Eric B. wrote:

[datasheets]
OK, I’ll look for them later on today.

Matt sent me the correct part number (MAX2118), and I’ve found the data
sheet.

The chip has a controllable IF-filter bandwidth. It can be controlled
using the set_bw method on the daugherboard subdevice. Pass it the
desired bandwith in Hz. The DBSRX code will accept a value between 1e6 and
33e6, though the chip’s only spec’d down to 4e6. By default we’re
running it wide open (33e6).

I’m going to play with this, thanks for the info!

Andreas

5

On Mon, May 18, 2009 at 07:11:43PM +0200, Andreas Bogk wrote:

The datasheets should be on Maxim’s site, though I think they’re
discontinuing the part. If you can’t locate them, let me know and
I’ll see if I can’t find one for you.

I can’t find them, and googling for MAX211x only brings me to Gnuradio
related information. Is there a magic part number I need to know? I’d
appreciate the datasheets,

OK, I’ll look for them later on today.

or alternatively the information that the
filters are indeed in the chip and not tunable.

The chip has a controllable IF-filter bandwidth. It can be controlled
using the set_bw method on the daugherboard subdevice. Pass it the
desired bandwith in Hz. The DBSRX code will accept a value between 1e6
and
33e6, though the chip’s only spec’d down to 4e6. By default we’re
running it wide open (33e6).

Eric

6

Marcus D. Leech wrote:

Arggggh! I knew it had to happen some day. What happens to DBS_RX
when MAX2118s aren’t
available any more?

We have plenty of chips and boards for the near future. They make a
replacement chip (MAX2112), which will require a board spin.

Matt

7

Eric B. wrote:

Arggggh! I knew it had to happen some day. What happens to DBS_RX
when MAX2118s aren’t
available any more?

–
Marcus L.
Principal Investigator, Shirleys Bay Radio Astronomy Consortium