Re: [Discuss-gnuradio] RA Receiver front end

[Marcus Leech]

If you already have an USRP, I might suggest the DBSRX receive daughtercard.

I have this configuration, and that's how I'm proceeding with my RA setup.
 The DBSRX can receive from 800Mhz to roughly 2300Mhz, which nicely
 covers both the hydrogen line, and the several OH+ lines.

The noise figure of TV tuners is generally terrible, but since any real
 RA type is going to use an LNA of as high quality (noise-figure and gain)
 as can reasonably be afforded, and situate it right up at the feedpoint,
 the noise figure of the tuner/downconverter is largely irrelevant.  Other
 factors, such as phase-noise will be important if you're doing 
fine-tooth-comb
 type spectral observations (such as would be required for SETI, for 
example).
 But for taking spectra of natural phenomenon (such as red-shifting), then
 the close-in phase-noise artifacts aren't going to be a big deal for you.

Digital TV tuner modules can mean a number of things.  Sometimes, they
 just mean "direct conversion", which produces an I/Q analog signal 
intended
 to be digitally manipulated to turn it into an MPEG stream.  Sometimes 
they
 mean that a digital (MPEG, typically) signal comes out of the tuner 
module.
 The DBSRX is based on a direct-conversion I/Q tuner chip, the MAX2118
 that converts the incoming signal at the chosen frequency into a 
"baseband"
 quadrature (I and Q) signal that stretches from DC to several dozen Mhz.


I have a paper that I wrote on my first direct-conversion RA receiver here:

http://www.propulsionpolymers.com/radioastronomy/seti_receiver.pdf

Frank Rawlins wrote:

> Hi Groups (sara and gnuradio),
>
> I am planning to use UHF TV tuner module and satellite TV tuner module for the 
> front end of RA receiver.  The frequencies of interest are 600MHz (TV antennas 
> are cheap!) and 1.4GHz.  I have a R-8500 receiver but choose the TV tuners 
> because of their wide bandwidth.  The IF of each can be amplified and fed to 
> integrator/DC amp or the IF could be fed to the USRP.
>
> I want to choose the best tuners with regard to Noise figure etc.  There is very little 
> on the internet regarding the specifications of each type.  The web site "TV tuners 
> in Donberg's Warehouse" list over a hundred TV tuners with prices but which one do I 
> choose? Could it be they are all the same to an industry standard specification? I have 
> some tuners from old wrecked TVs  Guess what? there is no model number on the modules.  
> Another problem - what about identifying the pin-outs?  There is one very good website 
> using a TV tuner UV916 building a 45-860MHz receiver (just put UV916 into search engine). 
>  I cannot find any more information regarding other types.
>
> Finally, I must admit I am confused between analogue and digital tuners.  Hope 
> someone has experience of TV tuners and able to help.
>
> Best wishes,
>
> Frank Rawlins
> South Coast England
>
>
>  

--
Marcus Leech                            Mail:   Dept 1A12, M/S: 04352P16
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