From: "Bob Lewandowski" <bob.lewandow...@vixel.com> Picosecond Pulse Labs (www.picosecond.com) manufactures coaxial DC blocks that operate from 700 Hz to >26 GHz (3 dB BW) and stand off 16 Vdc. You can also get a .086 in. diameter 'Semi Flex' coax cable from Tensolite/QMI (www.qmiinc.com). It has tin dipped bare outer braid and is more flexible than conventional semi-rigid coax. Cut the cable, strip back the outer shield and dielectric to expose about 0.1" of center conductor, solder the coax shield to the ground pad of a bypass capacitor location, and the center conductor to the capacitor pad connected to the power bus. Then insert the dc block ahead of the 8591E and look at the spectrum of the noise on the bus.
You can also measure bus impedance as a function of frequency by connecting a network analyzer to the same point by using a Smith Chart plot of S11. Calibrating the NWA and establishing the correct reference plane can be somewhat tricky in this process. The inductance of the traces and vias connecting the coax to the power and ground planes limit the low end measurement range at higher frequencies, but it may yield a useful comparison. --- From: "Raza, Ishfaqur" <ishfaqur.r...@intel.com> There is a HP Blocking capacitor, Model 10240B. It has BNC connections. I have used it in series with regular cables going to a spectrum analyzer to see the HF components on different surfaces. The component has 200V maximum DC tolerance. ------ From: Nitin Bhandari <nbhand...@extremenetworks.com> You might want to try to use a DC blocking capacitor in series with the probe. This will protect your analyzer input and still provide you with the information that you want - the noise spectrum. -------- From: "Bob Weber" <rwe...@txc.com> To make measurements like this with a 'scope or spectrum analyzer, I solder a thin coax (like RG-178) to the PCB where I want to make the measurement. Use vias to the planes that are near each other and unused by other components. Solder the shield directly to the gnd via, and solder the center conductor to the power plane via thru a 100nf SMT cap (overall lead must be very short). RG-178 with the TFE dielectric and FEP jacket lets you solder right on the coax without melting the insulation. Put a BNC or Type-N connector on the other end, and connect to the equipment of your choice (make sure there is an internal or external termination). Secure the coax to the board so that the vias are not stressed (or ripped off) by moving the cable. You can also use the same setup to inject noise into the plane with a signal generator and see what frequencies and noise levels cause the board to malfunction. ============= _______________________________________________________________________ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html _______________________________________________________________________ ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
