[time-nuts] Normal operating specs of a Morion MV89?
scott.j.stobbe at gmail.com
Sat Oct 1 19:44:18 EDT 2016
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 <kb8tq at n1k.org> wrote:
> > On Oct 1, 2016, at 4:08 PM, Scott Stobbe <scott.j.stobbe at gmail.com
> > If you used a 6db pad in conjunction with a 50 ohm termination you are
> > 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
> > On Friday, 30 September 2016, Tim Lister <listertim at gmail.com
> >> On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <scott.j.stobbe at gmail.com
> >>> 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
> >>> see how close you are to 50 Ohms output.
> >>> Roughly speaking it sounds like it will be in spec for amplitude, but
> >>> 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
> on a broken MV89.
> >> (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
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