[time-nuts] Normal operating specs of a Morion MV89?

Bob Camp kb8tq at n1k.org
Sat Oct 1 16:18:32 EDT 2016


> On Oct 1, 2016, at 4:08 PM, Scott Stobbe <scott.j.stobbe at gmail.com> 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 <listertim at gmail.com> wrote:
>> On Wed, Sep 28, 2016 at 3:30 PM, Scott Stobbe <scott.j.stobbe at gmail.com
>> <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.


>> (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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