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[Discuss-gnuradio] Better link to front end layout

From: cfk
Subject: [Discuss-gnuradio] Better link to front end layout
Date: Wed, 25 Feb 2004 17:18:21 -0800

Dear Guys:

    Thank you for all the comments today. I appreciate the help.

    Next, sorry about the mis-spelled link to the layout. It is
http://home.pacbell.net/cfk/frontendlayoutcomponent.pdf . Honest.

    I will change the schematic to include resistors to program the I2C
address for each 4702. The way it works is the voltage on MA0 can be ground,
dvdd, or 1 or 2 bands around a volt or so. There is a cute voltage
comparator in some of these I2C chips that allows one to set the voltage so
say 1.0V and get a different address. So, I'll put two resistors and include
a table for changing the I2C addresss of the 4702 tuner.

    I am also planning on changing the opamp to a Linear Technology LT1678,
which is a dual and sensing aux_dac_a for the first tuner agc and aux_dac_b
for the second tuner.

    I routed the board yesterday, but now I have a few changes. There are
currently 12 unconnecteds, but I should have that figured out Friday or

    The layout is just a two sided board. The component side has most of the
traces. The solder side is mostly ground plane, with some components and
some traces. I originally thought I might have to use a multilayer board,
but it seems to be coming together nicely as just a double sided board.

    Lets not worry too much about too many more features. I think the plan
should be to make a small fab run of 10 or so and ensure that the circuitry
is OK, there isnt too much ground noise, the analog circuitry works OK and
all of that. It is really easy to change the layout and make a second
revision. Since I dont have to pay anyone to lay it out for me, that works
out very well. I am mostly interested in making sure the 5->33V converter
works OK, the ground noise is small enough and the daughterboard doesnt
adversly affect the USRP for this revision.

    p.s. to Matt: Do you remember offhand which electrolytic model and
manufacturer you are using on the USRP. I would like to use the same part so
we can have a common parts list twixt the USRP and the frontend
daughterboard. It will be a little extra effort for me to check the bill of
materials, but I would rather like to be able to say "Matt have you got 10ea
10uf's you can matter transport to Irvine", or "Here, Matt, are some of
those tricky diodes you use elsewhere".


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