Products > Test Equipment
Rohde & Schwarz CMU200
Sas:
--- Quote from: Alfons on January 08, 2020, 08:00:24 pm ---After the signal has moved to the right for approx. 24 hours, it now runs to the left. That commutes back and forth about every 24 hours. The phase shift can hardly be seen with the naked eye. Is this commute normally?
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A question without a clear answer. It is not possible to set the frequency perfectly, the frequency deviation is always there.
We can only create wrong theories. Assuming that you set the ocxo generator perfectly, the GPSDO itself will change the phase shift once a day, along with the synchronization of the satellites with the standard time atomic clocks. Phase shift and drift to the left or right would be due to the low DAC resolution in GPSDO, one bit lower and one bit higher. This setting of ocxo alone is impossible, ocxo has too low accuracy. My cesium clock pulls phase shift over 36h and 2.8E-13 stability takes 5 days GPS tracking. I don't know if by chance the GPS update is currently not every 12 hours.
There are different ocxo generators, used after prolonged shutdown, shocks, shocks require several cycles to stabilize again. Frequency may depend on many factors. From temperature, reference voltage standard, supply voltage, output load, interference, altitude above ground, earth's magnetic field, etc. However, it most likely depends on ocxo consumption. Turning ocxo off and on again is a different frequency and never the same. Set with 0.01Hz accuracy at 10MHz. After many turns on and off, it will out of tune anyway :)
Alfons:
@Sas, thanks for the answer.
Some reports from users say, that the signals would run synchronously. But I can't imagine that either, because there will always be a slight drift. I'm still trying to figure out how big the drift is, how I calculate it. I have to familiarize myself with it, just out of interest. I think the accuracy that I have now is enough for the CMU200.
Ice-Tea:
Was a bit curious, so took a few pics of a "naked" TX/RX board. Figured I'd share. Not scaled. Enjoy!
Robert763:
--- Quote from: MasterTech on March 23, 2018, 10:14:26 am ---
--- Quote from: cmu2017 on March 23, 2018, 07:39:04 am ---- Is it possible to make a print screen save it a usb stick
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In my CRTU I bought a PCMCIA to SD adapter to make screen dumps, but all attempts with different card sizes have been unsuccessful, although someone told me it worked in his unit.
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This is an old post I know, but I just found it and can give you an answer. The CMU200 CRTU-RU basically runs DOS 6.22 and the PCMCIA interface uses the ATA (IDE) hard disc emulation mode. This mode uses a parallel interface and is not supported by SD cards as they only have a serial interface. Like wise the simple PCMCIA to SD adaptors do not support it either. Compact Flash (CF) cards do support ATA mode so a PCMCIA to CF adaptor will work.
dcarr:
I have a working CMU200 -> MMC (SD) card setup. See the pictures below for the PCMCIA adapter and the MMC card I use. I suspect that the it's important to use a SD (or MMC) card below a certain size...
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