Products > Test Equipment
Rohde & Schwarz CMU200
Ringmodulator:
Hi balage,
you can get them ready made with HMC213 for under 20$ delivered.
https://www.ebay.com/itm/HMC213-RF-Passive-Double-Balanced-Mixer-Diode-Frequency-Conversion-Module/264330247742
Chris
balage:
Hi Ringmodulator,
Oh, if I would have found the enclosed earlier, I would bought one. Especially HMC213 costs 15 bucks. ???
Anyway, it was fun to design my own board...
Sas:
@tech255 I have two .02 CMU, one older with PS2 and newer with USB. Both units are removed from the production line, have a generator +13dBm RF3 OUT and only 2W RF1 input. They also have a second generator, B41 and all GSM modules.
@Alfons B12 looks good. I don't know this Pulsar 510 oscillator. I think it is low phase noise ocxo. I calibrate my ocxo once a year, the error is less than 0.1Hz @10MHz.
I use the Anzac (macom) MDC-162 mixer. I amplify the IF from RX / TX module with a 40dB @2-4GHz old cascade amplifier mounted inside and powered from the CMU. At the amplifier output I have about +10dBm, good level to control the LO input of the mixer. Mixer conversion losses around 8dB, RF3 OUT generator output +13dBm level is enough to get 0dBm. I miss the AGC, because of course CMU has no normalization function for tracking generator.
Alfons:
Have now tried the B12-OCXO to compare with the GPSDO as a reference. After the GPSDO had been in operation for three days and nights continuously, I tried to take the phase curve on the oscilloscope to cover. Even without adjustment, the B12-OCXO signal was quite close to the GSPDO and only migrated very slowly.
The best thing I can set is that the signals move against each other at around 20ns per hour. If I turn the spindle trimmer just a mini-mini-tick, the direction changes, I can't find a sync. So there is nothing more. I might be able to get slightly better results by changing the value of the spindle trimmer, but I don't think that will work for long time. I guess everything will be slightly shifted again after restarting the GPSDO.
If I connect the GPSDO to the input of the CMU200, the integrated counter shows me the 10MHz down to 9 digits, the tenth digit oscillates between 1 and 0, the 11 digit fidgets. That is stable.
Alfons:
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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