Re: [Discuss-gnuradio] USRP for Radioastronomy

[Matt Ettus]

Marcus D. Leech wrote:
> Lamar Owen wrote:
> 
> 
>>How did you get the flatter baselines?  Was this through the DBS_RX or
>>baseband?  Did Charles see this?  :-)
> 
> 
> The DDC was set to -5.75Mhz.  Doesn't the TVRX produce a 5.75Mhz IF?
> 
> Perhaps (rampant speculation, and apologies to everyone, especially Matt,
>   if I'm wrong) the 40ft 21cm feed produces an IF that's in the passband
>   of the TVRX, and that's what we're looking at.  Or maybe it's something
>   else entirely.
> 


2 separate issues here --

Yes, this was recorded using the TVRX since the IF we were connected to
was at a very low level.

The reason the baseline was flat is independent of the daughterboard.
By sending 4 MS/s over the bus (4 MHz BW) and decimating by a factor of
4, you get the 1 MHz of BW you see in the figure.  Since we are looking
at the center 1 MHz, it is in the flat part of the passband.

Matt