I think you have mistaken the tilde symbol as a negative sign. Tim's 11 dBm is into the pad.
7 dBm +- 2 dB into 50 ohms is the spec for the mv89 no? On Saturday, 1 October 2016, Bob Camp <kb...@n1k.org> wrote: > HI > > > On Oct 1, 2016, at 4:08 PM, Scott Stobbe <scott.j.sto...@gmail.com > <javascript:;>> 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 <lister...@gmail.com > <javascript:;>> wrote: > > > >> On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <scott.j.sto...@gmail.com > <javascript:;> > >> <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 -- time-nuts@febo.com <javascript:;> > <javascript:;> > >> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
