Re: [Discuss-gnuradio] 4702 board

[Eric Blossom]

On Sat, Feb 07, 2004 at 05:55:45PM -0800, cfk wrote:
> Dear Eric:

>     After reading all of the archive today, one message in
>     particular caught my attention, and that was the "4702 tuners
>     available" message. I am wondering if a board to mount a 4702
>     along the lines of your "Microtune 4702 RF Frontend" schematic
>     with the addition of the +33V DC-DC converter might be an
>     appropriate adjunct for the usrp.

Definitely.  It would make a great daughterboard for the new USRP
revision that right now is in layout.  Matt can provide you the
mechanical and electrical specs.  In the meanwhile, here are some of
the relevant signals on the daughterboard bus: differential analog
input to main board, I2C bus, SPI bus, about 8 digital i/o pins that
can be controlled from the host software, 3.3V power and an
unregulated +5V supply.  The analog signal will connect directly to
the VIN+ and VIN- inputs of an AD9862.  You've also got access to the
AUX DAC {A,B,C} and AUX ADC {A,B} of the AD9862 if you need them.

>     This simple board could exchange its DB-25 for a header to
>     jumper directly to the usrp and could be of the same form
>     factor. It could also have the additional interface circuitry
>     added to provide the I & Q signals directly to two of the ADC
>     inputs.

Sure.  Each Rx daughterboard provides both I & Q.

>     I am also thinking that there could be either a power connector
>     for an LNA connected to the 'F' connector input, an LNA on the
>     board or footprints for both. Personally, I am a bit more
>     inclined to think the noise figure is a little better if the LNA
>     were a seperate little cube connected directly to the 'F'
>     connector, rather then on the board, but that is an incomplete
>     thought at the moment.

FYI, the 4702 has an IEC connector, not an F connector.  Perhaps you
build your LNA (switchable in and out) on the daughterboard, cable it
up to the IEC connector and provide either a BNC or F-connector as you
see fit. 

>     I suppose that power connectors could also be shared allowing
>     one power supply to power both a usrp and a "4702 FrontEnd".

We should have enough power through the daughterboard bus to power the
module.  There won't be enough juice for high power xmitters, but that
won't be a problem with this Rx module.

>     If this idea is interesting, it could lead to a family of
>     front-end-down-converters all in a similar form factor for
>     various SDR types and various projects. I personally see the
>     different uses of gnuradio as needing different front ends for
>     different projects as the "universal front end" appears to be a
>     non-realizable dream at this time.

We're all on the same page.  When Matt gets some breathing room he'll
be publishing the mechanical and electrical specs for the whole system,
but particularly the specs for the Tx and Rx daughterboards.

>     Please let me know what you might think of this idea.

Great idea.  We definitely want lots of "plug and play" daughterboards
for the new USRP.  Each daughterboard will also have a bit of EEPROM
(24LC024 or 24LC025) on it that identifies the board.  The host
software will be able to query the motherboard and determine what
daughterboards are loaded.

> Charles Krinke

Eric