Re: [Discuss-gnuradio] Practicality of DC-light RF front-end?

[David Bengtson]

Marcus D. Leech wrote:

> I've been thinking about the practicality of a "DC-light" RF receiver
>  front end, for radio astronomy in particular, but also for general use.
>
> It seems to me that something like the MAX2116 (or similar direct-conversion
>  satellite receiver) having a very wide tuning bandwidth (over 1Ghz), could
>  be used as part of a very wideband receciver front end.
>
> My idea would be to use the MAX2116 directly for signals between 950Mhz and
> 2150Hz, and
>  to use a an UP-conversion stage for signals between about 5Mhz and 950Mhz. 
> The idea would
>  be to use another LO, at perhaps 945Mhz (just below the passband of the
> MAX2116), and mix
>  the incoming signals with that, filter, and feed to the MAX2116.  A small
> collection of
>  PIN diodes could be used to route the RF where it needs to go.
>
> Building a 945Mhz fixed-frequency LO wouldn't be that hard, and mixers are cheap
> and
>  plentiful.
>
> What do people think about something like that?
>
> Other wideband receivers often use a collection of synthesizers and VCOs to
> cover the
>  wide bandwidth, but in this scheme, there's only 1 synthesizer to program, and
>  a little RF switching.
>
>  
The big problem with this approach is the required receiver dynamic 
range. 100 dB or more isn't really out of the question for a general 
receiver front-end dynamic range, so you'll need 16 to 18 bit of 
effective digitization to make it work. This is do-able for a 10 to 20 
MHz wide bandwidth, but not at this point in time.

There was a good presentation at SDR Forum last month about the 
problem's with A/D converters in the DC-daylight range. I have the 
goodies at work, I'll dig it up and relay the detail's next week.


Dave