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Rohde & Schwarz CMU200

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msraya:
Hello All!!

I made test with the item...
I disasemble the CMU200 and then before installation the SA keep working.. no trace in screen..  :palm:
It appears that the TXRX board is not settle in place.. Then It worked again  :phew:

So I put out the screening and Put the connector in place, only worked in the place that says Brainbox.
I put the BNC Bulkhead connector in the front plate in the Audio output conector. Then I put the Bulkhead of the audio signal in the rear panel of the unit.. No problems so far..

I put 12V at board and connect the board with little microwave sma cable.. I put 3dB pad after TG generator and adjust to obtain flat response. You can see in the photos...

Then I take a 10.7MHz crystal filter 25KHz BW i cannot remember...
You can measure about 20KHz BW..

It works a treat..  :-+  You can compare the trace with a Rigol TG.. The response is practically identical.
At 100 Hz the noise floor of the R&S is about -100 dBm..

The interface of the R&S is poorer than RIGOL, but it works..

P.D: I try to use 1916.2 MHz with the second internal generator to use the first generator at 100MHz with an input mixer and to sweep from 0 to 1.2GHz...  To test 455KHz Ceramic Filters...

BUT, It doesn't work because the BG7TBL design is using a filter post mixer that have a high frequency passband above 10MHz and the signal below 10MHz is greatly attenuated, so it doesn't appear in the screen....
I think also the mixer cannot work at these low frequency..

I would use a two mixer configuration to translate to 0 MHz..

Regards
Manuel

Brainbox:
The second generator only goes to -60 dBm output power, probably that is too low for the mixer to give sufficient output ?
Indeed the BG7TBL design seems to cuts off from 10 MHz and beneath, but that is the same for the CMU itself.

Nevertheless; with this extension the CMU200 becomes of great value for me.

For frequencies beneath 10 MHz I do use an up-convertor which lift 0-10 MHz by 10 MHz to a useful 10-20 MHz.
Setting the RF generator to 1826.115 MHz in combination with this unit will give you a tracking extension in the 0-10MHz region.

I build the CMU together end mounted the bulkhead at a spare location at the back, the AF positions at the front are already used by the audio extension.
To place the air duct covers back in place I had to drill a hole in one of the plates.

Ericmax:
Hi all.

small test with FreRes64 V5.25.
RF3 to RF1 and RF3 to RF2.
RF3 set 0dBm in FreRes.

10 to 2700Mhz step 10 Mhz.

RF3 out verified with my URV35 + NRV-Z6
i have same graphic of Rf power.

4dB difference from 10 to 2200 Mhz, may be a small problem on this CMU RF unit.   :-//

_Wim_:

--- Quote from: Ericmax on August 21, 2016, 06:54:00 pm ---Hi all.

small test with FreRes64 V5.25.
RF3 to RF1 and RF3 to RF2.
RF3 set 0dBm in FreRes.

10 to 2700Mhz step 10 Mhz.

RF3 out verified with my URV35 + NRV-Z6
i have same graphic of Rf power.

4dB difference from 10 to 2200 Mhz, may be a small problem on this CMU RF unit.   :-//

--- End quote ---

Do you have the same result if you add some dwell time (to let the generator stabilize)? I can't test on mine right now, but will do when I am back at home.

richnormand:

--- Quote from: ZL1CVD on May 06, 2016, 07:54:46 am ---Just upgraded an 8924C for a CMU-200. It has a fault - internal RF loop path 1 test fails. Does anyone have any ideas where I should start? Also does anyone happen to have service manual with circuits - the one i have is missing all module exploded diagrams and circuits. Next step for me it to install a SSD. Cheers.

--- End quote ---

Going back to OPs question:

I have read through the entire thread and did not see if the issue had been resolved.

After fixing the PSU and the LCD display ( https://www.eevblog.com/forum/repair/rohde-schwartz-universal-radio-communication-tester-cmu200-psu-issues/  )  the unit passes all diagnostics tests except the internal RF loop and the 1->4 2->4 external loop.

Before going back in the box I wondered if this is a common problem that is well known in the community. :-//

Cheers and thanks.

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