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. On Wed, Sep 28, 2016 at 4:58 PM, Tim Lister <lister...@gmail.com> wrote: > On Wed, Sep 28, 2016 at 11:46 AM, Tom Miller <tmiller11...@verizon.net> > wrote: > > Just put a 47 or 56 ohm resistor from the output pin to ground and look > at > > it with a X10 scope probe. > > > > Do you get a sine wave? Over 1 volt pp? > > Hi Tom, Scott, I used about two feet of a (Pomona) coax to > minigrabbers test lead and connected it direct to the scope and set > the attenuation to 1x in the channel menus. I attached the > minigrabbers to the RF and GND pins on the Morion since I didn't fancy > holding a probe near the ~50 degree C Morion case.. I got a nice clean > sine wave and the in-scope measurement routines reported 2.3 V > peak-to-peak. I had 1V/div set so I could fit the OCXO and GPSDO > outputs on the scope screen for comparison. (I haven't been able to > get a screen capture yet as I need to find a small enough capacity USB > key that will be supported by the scope) > > Tim > > > > > Otherwise, you can open up the can and replace the output chip capacitor. > > > > > > Regards > > > > ----- Original Message ----- From: "Scott Stobbe" < > scott.j.sto...@gmail.com> > > To: "Discussion of precise time and frequency measurement" > > <time-nuts@febo.com> > > Sent: Wednesday, September 28, 2016 2:38 PM > > Subject: Re: [time-nuts] Normal operating specs of a Morion MV89? > > > > > > > >> If you used a 10x probe (10 Meg || 10-15 pF) you may have a pretty weak > >> output, but if you could drive a meter of coax or a 1x probe to 800 > mVrms > >> at 10 MHz your probably not too far off spec. > >> > >> 100 pF at 10 MHz is 160 Ohms. > >> > >> On Wed, Sep 28, 2016 at 12:39 PM, Tim Lister <lister...@gmail.com> > wrote: > >> > >>> On Wed, Sep 28, 2016 at 4:14 AM, Bob Camp <kb...@n1k.org> wrote: > >>> > Hi > >>> > > >>> > You have one of the many MV89A’s with an output problem. To be > > >>> > absolutely > >>> > sure of the output, you need to have the scope set to 50 ohm input. > If > >>> it was set > >>> > to Hi-Z, the output is likely even lower….. > >>> > >>> It seems that the scope is 1 MOhm input impedance and is not > >>> changeable. I will have to see if we have any 50 Ohm in-line > >>> terminators around that I can also borrow. Does anyone think that > >>> there is any value in trying to pursue a return and replacement with > >>> the ebay seller (being China, it's likely to be a long round-trip time > >>> for both messages and parcels) or just live with it and move on > >>> (potentially replacing the capacitor later if I get some way of > >>> getting the casing open safely). From what Bob and others have said, > >>> it seems that most of the MV89's have this problem so it seems > >>> unlikely I would get a better one without a lot of trials. > >>> > >>> Tim > >>> > >>> > > >>> > Bob > >>> > > >>> > > >>> >> On Sep 28, 2016, at 1:38 AM, Tim Lister <lister...@gmail.com> > wrote: > >>> >> > >>> >> On Tue, Sep 20, 2016 at 12:56 PM, Bryan _ <bpl...@outlook.com> > wrote: > >>> >>> May also want to check the output amplitude. If memory serves me > >>> correct it is very common for a capacitor inside this model number to > >>> fail. > >>> It can be fixed but requires a torch or a pretty heavy duty soldering > >>> iron > >>> to get the can open. > >>> >>> http://www.rbarrios.com/projects/MV89A/ > >>> >>> > >>> >>> -=Bryan=- > >>> >>> > >>> >> > >>> >> I managed to borrow a Tek TDS 2024B 200 MHz scope from work and > hooked > >>> >> it up to the output of my MV89A. I get a peak-to-peak measurement of > >>> >> 2.3 V which if I have converted it right is ~11 dBm ? Alternatively > if > >>> >> I turn on the FFT mode on the scope I get a peak value of -2.17 db > if > >>> >> I am driving the cursor mode correctly. With the 10 MHz from the > >>> >> radioshackus GPSDO used for triggering, it takes ~18 seconds for the > >>> >> MV89 waveform to drift 1 cycle (this is without anything connected > on > >>> >> the Uin or Uref pins). > >>> >> > >>> >> Tim > _______________________________________________ > 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. > _______________________________________________ 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.
