Thanks, everything is clear now. I will have a try with a pair of Schottky diodes as 10 db give 3.16 attenuation and so no enough for a +-15V rails , I want to be sure ;=) ) Regards Loïc
-----Message d'origine----- De : [email protected] [mailto:[email protected]] De la part de John Miles Envoyé : mardi 25 octobre 2011 22:55 À : 'Discussion of precise time and frequency measurement' Objet : Re: [time-nuts] 8560E DC Coupling phase noise measurements > -----Original Message----- > From: [email protected] [mailto:time-nuts- [email protected]] > On Behalf Of Loïc MOREAU > Sent: Tuesday, October 25, 2011 1:01 PM > To: [email protected] > Subject: [time-nuts] 8560E DC Coupling phase noise measurements > > Hi, > In the process of measuring phase noise with a 'demphano' gear, I am > a bit > reluctant to connect my 8560E in DC mode to get 30 Hz low frequency > sensitivity: the SA input is very sensitive to DC voltage and may be > destroyed by a voltage larger than 200mV. > > So with a LNA having no blocking DC output I would like to know the > best way to protect the SA. > > I suppose that putting a 100µF capacitor between LNA and SA is not > especially a good idea as a charged capacitor to DC rail may have the > same effect that no caps at all. > > I am looking for some advice in that domain to pursue phase noise > measurements, for now I connect the SA with a caution after PLL lock > and measuring the SA input with a DC voltmeter before switching to DC > SA input but this mode of operation is a bit frightening. > > Any idea ? The 200 mV limit is only with 0 dB of RF attenuation. With a quadrature PLL and LNA, you don't need to use 0 dB. 20 dB is probably OK, and if not, you can make up for it with more gain. A pair of back-to-back Schottky diodes would be another alternative. -- john _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
