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Re: [Discuss-gnuradio] FrontEnd4702 take 2

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] FrontEnd4702 take 2
Date: Tue, 24 Feb 2004 21:17:05 -0800
User-agent: Internet Messaging Program (IMP) 4.0-cvs

Quoting cfk <address@hidden>:

     The changes relate to trying to make the board per the USRP mechanical
> constraints firstly. I made the board 2000 mils hi X 2450 mils wide. The
> growth is on the left side as viewed from the top of the USRP with the board
> in the upper left slot. I made the mounting holes per the 150mil setback
> (first three) and the 300mil setback (bottom right corner).

Sounds good

>     I did add 10uf, 0.1uf and 1000pf on dvdd, avdd and +5. Additionally, I
> put an opamp in place of the MAX518 and am driving it from aux_dac_a from
> the USRP. Currently I am thinking MAX406, but I may change to a Linear
> Technology LT1678. If anyone has a better idea, I am all ears (even have my
> Mickey Mouse hat available with extra ears).

All good choices.

>     There are now two 4702 tuners on the board. The first one has its MA0
> pin grounded so it should respond to I2C address 0xC0 and the second has its
> MA0 pin left open so it should respond to I2C address 0xC2.

While we're at it, let's really go all out -- the 4702 can handle 4 different
addresses.  Thus, we could put 2 of these boards, with 2 4702s each, on the
USRP at once, necessitating the 4 addresses.  With a pair of 2-pin jumpers we
can accomodate that.  If you give the address select pin on one 4702 a 15K R to
+5V, and then provide a jumper which can pull that to ground, it will be
selectable.  Similarly the other one could have a jumper to +5V, and would be
open otherwise.

>The agc voltages
> are common, although if you think the opamp should be a dual and use the
> aux_dac_b, that is OK with me.

I would go with a dual opamp and use both DAC outputs.

>     The schematic has grown to two B size pages and they are
> http://home.pacbell.net/cfk/frontend4702_1.pdf and
> http://home.pacbell.net/cfk/frontend4702_2.pdf

They look good.

>     The layout is shown as an Xray view through the board and is at
> http://home.pacbell.net/cfk/frontendcomponent.pdf . Please view it as a
> parts placement idea only at this time as it isnt routed yet. I am hopeful
> that I will be able to make it just a double sided board. That is, the
> component side will have most of the traces. This leaves the majority of the
> solder side as a ground plane with traces as required in it. I will route
> the power supply lines as wide traces. Currently, signal traces are planned
> at 12mils and the power supply traces at 25mils or in a couple of long
> cases, 50mils.

That file seems to be missing from your site.

> side p.s to Matt: Is the schematic file available for study by me?

Yes, I'll get you a copy of the schematics.


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