Hi The sensitivity of BNC connectors goes up quite a bit as they wear out. Both sides of the connection are subject to wear. Replacing both sides is often the only solution when they get noisy. That said, “screw down” connectors are a better way to go.
The “capacitive loading” termination of the mixer is something that a number of us tried to reproduce when the paper came out. Even after fairly extensive conversations with the authors, the effect seems be quite difficult to reproduce. It certainly is not a “general solution” to the problem. Bob > On Mar 25, 2016, at 5:55 PM, Bruce Griffiths <[email protected]> > wrote: > > As long as BNC connectors are avoided as their phase shift isnt that stable.. > A small mechanical disturbance will change it significantly. Actually low > noise PN measurement systems can be very sensitive to cable movement. Bolting > modules to a metal baseplate helps a lot as does using intermodule > connections comprising SMA(m)-SMA(m) barrels rather than cables. > There's also the question of mixer port termination.The nist paper by Walls > and Stein indicates that capacitive termination of the IF port may be > effective in reducing noise whilst maintaining a flat response fro dc to > around 50KHz.Small value resistors in series with the RF and LO ports are > then useful in reducing the VSWR. > Bruce > > > On Saturday, 26 March 2016 10:10 AM, Bob Camp <[email protected]> wrote: > > > > Hi > >> On Mar 25, 2016, at 1:55 PM, jimlux <[email protected]> wrote: >> >> On 3/25/16 5:07 AM, Bob Camp wrote: >>> Hi >>> >>> The reverse isolation issue is indeed one of the weaknesses of this setup. >>> For testing >>> OCXO’s isolation is not a big deal. A normal OCOX has very good output >>> buffering >>> to give it the stability you are after. If you are running (maybe) a VCO >>> with no buffering, that >>> assumption falls apart. The VCO will / can injection lock through the >>> mixer. In that >>> case you *do* need an amp to provide enough isolation to prevent the >>> injection lock. >>> >> >> >> But if someone were building a little module for a cheap and cheerful noise >> analyzer, then the buffer amp would be a separate module. > > That’s how I have always done it in the past. The need for the bufferer is > rare enough that including it in the > basic analyzer module is not cost effective. The HP 3048 has the same basic > issue (isolation) and they made > the same decision there. > > Bob > > >> >> _______________________________________________ >> 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. > > > > _______________________________________________ > 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.
