I don t have my notes here, but are these numbers not for the 11729C system including the 8662A rather than for the unit standalone? So as long as you are measuring > 20-30 MHz the difference 848/729 should be much smaller than indicated, or be attributed to the ref?
Xtof. Adrian wrote: > I tried to measure phase noise of a 10811A, but found out that the > specified PN is below the noise floor of my 11729C. > > Can anyone tell why the (phase detector method) PN noise floor is so > much different between the two units? > > 11729C at 100 Hz -126 sBc/Hz (-133 dBc/Hz typ.) > 11729C at 1 kHz -135 dBc/Hz (-140 dBc/Hz typ.) > > 11848A at 100 Hz -150 dBc/Hz (-160 dBc/Hz typ.) > 11848A at 1 kHz -160 dBc/Hz (-170 dBc/Hz typ.) > > Some 25 dB is quite a difference, isn't it? > > Basically, both units apper to be not that much different, except that > the 11729C has an IF amp and power splitter between the input and the > PD L port, while on the 11848A the L input is fed directly into the > mixer. There are some differences in the LNA circuits, but that > shouldn't be responsible for the huge noise floor difference. > > 11929C requires 0 dBm (-5...+10 dBm) 'L' (MW Test Signal) input level, > that is amplified by the IF amp to >+10 dBm at the mixer input. Btw. > the IF amp saturates at input levels grater than -50 dBm. For the 'R' > input (5-1280 MHz), the manual specifies -1...+1 dBm. > > For the 11848A, the L input is +15...+23 dBm, and 0...+23 dBm at the R > input. Below +15 dBm L and R, the system degrades considerably. > Reducing 'L' to +7 dBm adds 10 dB to the noise floor. Reducing 'R' > below +15 dBm adds directly to the noise floor. So, reducing it to 0 > dBm would add 15 dB to the noise floor. > > So, it looks like the 11729C phase detector is more like a +10 dBm > mixer, while the 11848A has a +17...+23 dBm mixer. > > Replacing the 11729C PD with a ultra high level mixer should get the > noise floor close to 11848A specs. It would just require to feed L and > R directly into the mixer rather than using the instrument inputs. > > Any thoughts / experiences referring to this? > > Adrian > > _______________________________________________ > 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. -- Christophe Huygens Dept. Computer Science E-mail: [email protected] Celestijnenlaan 200 A. bus 2402 B-3001 Leuven, Belgium Tel: +32 16 32 70 88, Fax: +32 16 32 79 96 Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm _______________________________________________ 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.
