Re: [Discuss-gnuradio] 4702 usrp daughterboard

[Eric Blossom]

On Sat, Feb 07, 2004 at 10:20:24PM -0800, cfk wrote:
> OK Eric:
>     I have PADS, but I'm a bit faster with Orcad Layout. I'm mostly a
> software guy, but I find the occaisional board layout is actually relaxing.
> But then all software guys are crazy as we know. PDF, ASCII & Gerber it
> shall be.
> 
>     50mm x 50mm, hmmm. Well, the 4702 appears to be 65.4mm long x 12.6mm
> wide so its a bit big for a 50mm x 50mm board. I really wanted to have it on
> a board and not loose. I was thinking of a board that was more like 100mm x
> 100mm (or 4 inches square). Maybe we need to go back and forth with a couple
> of mechanical's.

I believe there are two free dimensions on the Rx boards.  Matt will
provide details soon.  There will be room to get it all solidly
mounted.  It has to be that way; there are electrical connectors down
the length of it ;-)

>     I printed out the usrp picture and the schematic, but I dont know which
> digital interface connector is which yet. Do you have the silk in a gerber
> or perhaps the assy so I can try to figure out how to put the 5 pounds of
> parts into the 2 pound bag.

The picture and schematics are for the rev 0 USRP.  It didn't have any
of the daughterboard stuff, just the SMA connectors.  What we are
talking about is the new revision (which needs a name or number or
something).

> > I think you can get by without a demodulator.  Assume bandpass
> > sampling and put the 36 MHz IF into a single channel (I). You can
> > probably do this with a mini-circuits RF xformer.  Properly terminate
> > the Q input and you're done.  The A/D's are running at 64 MHz so
> > you'll fold down to 4 MHz which is not so great for the 8 MHz SAW, but
> > OK for 7 MHz.  Matt: comments?
> >
> 
> On this one, could you consider a sketch of the circuit with the transformer
> you have in mind? I suspect your mind is closer to what the AD9862's feel
> happy with then mine right now and I would hate to mess up the interface
> twixt the 4702 adn the AD9862 with some silly impedance mistake. For some
> reason, I was thinking that we wanted to feed the usrp with both I & Q and
> put OPA681/OPA691's hither and dither. I need you to straighten me out a bit
> on the transformer, termination of the Q input and opamps a bit.

Either Matt or I will take a shot at this in the next couple of days.

> > Send me your snail mail address and I'll get a couple of modules out
> > to you.
> 
> Its Charles Krinke, 15 Bayside, Irvine, CA 92614 (949) 551-1838.

They'll go out Monday.

> I am beginning it might be a good idea to bring the spare DAC pin from the
> MAX518 over to a header so we can use a 3 pin MTA-100. That way we can have
> ground, power and an optional RF Gain for a VGA (Variable Gain Amplifier)
> instead of just a fixed gain LNA. I know VGA's are more expensive then
> LNA's, but having the signal there seems reasonable.

OK.

Eric