HI > On Oct 1, 2016, at 4:08 PM, Scott Stobbe <[email protected]> wrote: > > If you used a 6db pad in conjunction with a 50 ohm termination you are spot > on. If you used a 6dB pad as a 50 ohm load, the effective load will be a > bit higher than 50 and the attenuation less than 6 dB. Either way sounds > like the output stage of your OCXO is in spec for 7 dBm into 50 ohms.
The scope is reading -11 dbm after a 6 db pad? Not sure where 7 dbm comes from. > > On Friday, 30 September 2016, Tim Lister <[email protected]> wrote: > >> On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <[email protected] >> <javascript:;>> wrote: >>> You are certainly no where near -40 dBm into 50 ohms as the blog Bryan >>> posted above. Your setup may have 70-80 pF of load (~220 Ohms), if you >> also >>> measured the output voltage with a 10x probe you could work backwards to >>> see how close you are to 50 Ohms output. >>> >>> Roughly speaking it sounds like it will be in spec for amplitude, but to >>> definitive you will have to load it with 50 Ohms as others have >> suggested. >>> Anything can work plug your bnc cable into a 50 Ohm input instrument >> (even >>> if its ancient) and measure the output voltage on the OCXO with a 10X >>> probe. Or a near enough to 50 Ohm resistor as Tim suggested. >> >> I obtained a (Pomona I think) 50 Ohm terminator/6db attenuator The 6 db pad >> and >> repeated the measurements with the MV89A, connecting the RF and GND >> pins through a BNC cable and the terminator directly into the Channel >> 1 of the scope . I now get an amplitude on the scope FFT of -6.99 dB >> measured with the cursors. According to the scope manual this is >> referenced to 1 V rms so this would give a Vrms equivalent to -0.99 dB >> i.e. 0.89 Volts. Assuming I've done the rest of the maths conversions >> right, this would give a peak-to-peak value of 1.26 V and a power of >> ~11 dBm. The -11 dbm. That sounds a lot more like -5 dbm than +7 dbm. This is a pretty typical output on a broken MV89. Bob >> (Assuming everything worked alright, I put the scope captures >> up on our Owncloud at >> https://cloud.lcogt.net/index.php/s/pHBV6EORT33ucjA - Channel 1 is the >> MV89A, Channel 2 is the GPSDO output) >> >> So I think this means my unit is behaving OK ? >> >> Cheers, >> Tim >> _______________________________________________ >> time-nuts mailing list -- [email protected] <javascript:;> >> 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.
