Re: [Openbts-discuss] 52 MHz clock oscillator - clock output spec

[Eugene B. <eug...@sa...>]

Can the DACs be ranged? For example, just provide an analog voltage between 1.5 (00h) and 2V (255h) so the 8 bits are focused on the 0.5V range?

Eugene Blanchard
Instructor
School  of Information and Communications Technologies
SAIT Polytechnic
(403) 774 - 4875
Broadcast Systems website http://broadcast.sait.ca
Telecom Systems website http://telecom.sait.ca


-----Original Message-----
From: Matt Ettus [mailto:ma...@et...] 
Sent: Wednesday, February 02, 2011 4:48 PM
To: Eugene Blanchard
Cc: OpenBTS
Subject: Re: [Openbts-discuss] 52 MHz clock oscillator - clock output spec

> -----Original Message-----
> From: Matt Ettus [mailto:ma...@et...]
> Sent: Wednesday, February 02, 2011 10:35 AM
> To: Eugene Blanchard
> Cc: OpenBTS
> Subject: Re: [Openbts-discuss] 52 MHz clock oscillator - clock output spec
>
> On 01/31/2011 11:24 AM, Eugene Blanchard wrote:
>> Excellent points. The TCXO that I had built is actually a VCTCXO so
>> it would work by software control. Looking over the USRP docs at
>>
>> http://gnuradio.org/redmine/wiki/gnuradio/UsrpFAQ
>>
>> I see that there are eight auxiliary 8 bit D/A output ports available
>> on the USRP. Four of the eight are assigned to RXA/TXA and the other
>> four to RXB/TXB. Are all eight being used? Would it be possible to
>> use one for control of the VCTCXO?
>
>
> There are 4 channels going to each daughterboard.  No existing
> daughterboard uses channels C or D, I would suggest using one of the C
> channels.


Just to expand on what I said here...  The "C" DACs are 8 bits.  The "D" 
is actually 12 bits, so if you need more resolution, it might be useful. 
  However, D is a sigma-delta converter, and may need a little extra 
filtering.  There already is a filter on board, but more can't hurt.

Matt