[Discuss-gnuradio] top-posting considered harmful

[Eric Blossom]

Folks, please trim your posts.
Do not top post like I just did (to illustrate what I'm talking
about).  For that matter, don't blindly bottom post either.  
Note the 5 copied messages. 

Thanks,
Eric



On Wed, Mar 07, 2007 at 02:52:18AM -0800, Brett Trotter wrote:
> 
> Out of curiosity, what generation USRP do you have? My Rev 3 board has quite
> a lot of clearance on the TX-B side (1/4"ish- not measured)
> 
> 
> Weber, Michael J. (US SSA) wrote:
> > 
> > I have identified the cause of the shorting issue I was experiencing and
> > thought I would share. The bottom-left corner mounting hole of the USRP
> > passes very close to the internal heat sink pad for the 3.3V regulator;
> > this pad is at 3.3V due to the regulator design (tab is hot). Some of
> > the green board mask had scraped off when the mounting post for the Side
> > B daughtercards was installed, which brought that mounting post, and by
> > extension the enclosure, to the 3.3V potential. Photos of the board site
> > are at http://www.likesgadgets.com/gr/  When the SMA jumpers connected
> > the ground to the case, a short occurred.
> > 
> > I was also able to reproduce the short out of the enclosure just by
> > tightening down the mounting screw for a daughterboard into that same
> > mounting post; the lock washer bit through the daughterboard mask and
> > shorted the daughterboard ground plane through the mounting post to the
> > 3.3V heatsink pad.
> > 
> > Even though there is no lock washer between the mounting post and the
> > 3.3V regulator heatsink pad, the raised edge of the pad caused the mask
> > to rub off when the mounting post was tightened (or perhaps earlier, who
> > knows?)
> > 
> > The short term solution is to insulate the side B mounting post from the
> > 3.3V pad with a very thin insulating washer, scotch tape, or perhaps to
> > not mount that post. This prevents the enclosure from being connected to
> > the +3.3V buss when we really do want it grounded. If the washer is too
> > thick it will cause the daughterboard to bend or not fully seat in the
> > nearby connector.
> > 
> > IMHO, the long term solution for the next batch of USRPs is to increase
> > the clearance between the mounting hole and the 3.3V regulator heatsink
> > pad that the hexagonal mounting stud does not cover or touch the pad.
> > That will prevent problems for folks with overenthusiastic fingers. :-)
> > 
> > Best,
> > Mike
> > 
> > 
> > -----Original Message-----
> > From: address@hidden
> > [mailto:address@hidden
> > On Behalf Of Weber, Michael J. (US SSA)
> > Sent: Friday, March 02, 2007 11:58 AM
> > To: George Barrinuevo; address@hidden
> > Subject: RE: [Discuss-gnuradio] USRP + case = electrical short??
> > 
> > George, thanks for the information!
> > 
> > I would be very surprised if the USRP design did not intend to allow for
> > RF grounding to a case, but I supposed it's possible. Good grounding is
> > essential to good RF performance, especially with the proximity of the
> > analog and digital circuits.
> > 
> > Matt, is this in fact the design, or is this behavior a fluke?
> > 
> > Thanks,
> > Mike
> > 
> > -----Original Message-----
> > From: address@hidden
> > [mailto:address@hidden
> > On Behalf Of George Barrinuevo
> > Sent: Thursday, March 01, 2007 8:56 PM
> > To: address@hidden
> > Subject: Re: [Discuss-gnuradio] USRP + case = electrical short??
> > 
> > Hello,
> > 
> > I experienced a similar issue with my BasicRX and other daughterboard.
> > Here is what I found.  When all is working fine, the motherboards green
> > LED blinks. 
> > Otherwise, it does not blink or come on when there is a short.  When I
> > loosened the nut/washer that holds the SMA jumper cable to the case, the
> > short went away.
> >  It appears that when this nut it tightened too much, the locking washer
> > will bite through the black pant on the enclosure and make contact with
> > the enclosure metal which causes a short.  My solution was to loosen
> > this nut a bit.
> > 
> > A better solution is to find plastic thin washers and use this instead
> > of the locking washers supplied with the enclosure.  However, I was not
> > able to find a plastic washer in the right size.  Someone on this
> > mailing list used a sheet protector with an exacto-knife to cut out a
> > shape of a washer.
> > 
> > Does anyone have a better/easier solution to this problem?
> > 
> > Thanks,
> > 
> > --- "Weber, Michael J. (US SSA)"
> > <address@hidden> wrote:
> > 
> >> Hello,
> >> 
> >> I have a USRP with an RFX2400 mounted on the A side and a FLEX900 
> >> mounted on the B side. Everything works great UNTIL I connect the SMA 
> >> jumpers from a TX/RX port on either board to the case. When the 
> >> connection between the TX/RX ground and the case is made, a short 
> >> occurs, the regulator gets very hot, and the voltage at the input jack
> > 
> >> drops to about 2V. Of course I disconnected the power as soon as I 
> >> discovered what was happening. The board seems happy out of the case, 
> >> or even in the case if the antenna port jumpers are not installed. I 
> >> have to other units just like this one running with no problems, 
> >> though one of them has a FLEX400 instead of a FLEX900.
> >> 
> >> So... any ideas where the short is? I inspected the case and USRP but 
> >> didn't see anything telling, but there's a lot of tiny components and 
> >> traces.
> >> 
> >> Help?
> >> 
> >> Thanks,
> >> Mike
> >> 
> >> -----------------------------
> >> Mike Weber * 703-668-4516
> >> Network Engineer, BAE Systems
> >> 
> >> 
> >> _______________________________________________
> >> Discuss-gnuradio mailing list
> >> address@hidden
> >>
> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >> 
> > 
> > 
> > George Barrinuevo
> > address@hidden
> > 
> > 
> > 
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> > 
> > 
> > 
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> > 
> > 
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> > 
> > 
> 
> -- 
> View this message in context: 
> http://www.nabble.com/RE%3A-USRP-%2B-case-%3D-electrical-short---EXPLAINED-tf3358833.html#a9350646
> Sent from the GnuRadio mailing list archive at Nabble.com.
> 
> 
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