Rohde schwarz CMS50

[JasperNL]

Hi all,

I have the opportunity to buy a Rohde Schwarz CMS50 radio test set from my employer. Before I make the purchase I would like to know if the device is fully functional. I am testing and figuring out all the functions. I’m a bit confused with the following results:

First image:
Connected a 434Mhz antenna to the high power INPUT 1 jack. Creating a RF signal with my remote car key. The device measures -33dBm.
Second image:
Connected a 434Mhz antenna to the low power INPUT 2 jack. Creating a RF signal with my remote car key. The device measures -72dBm.

Why is there a 39dB difference between the channels? Is the input 2 damaged and reading low? Is there a setting that can cause this difference? Or replace user?





Second situation:
INPUT 1 jack is connected to INPUT 2 jack with a 50E coax. Device is operating in tracking mode.
First image: output power: 0dBm
First image: output power: -10dBm
First image: output power: -20dBm
First image: output power: -40dBm

I would expect that the measured power is about the same as the source power. But the measured power is about 55dBm lower. Consistently for the different output power settings.
Why?






Thanks in advance!
Greetings Jasper
Netherlands

[dave_k]

Start by setting the input attenuation to manual ..

[JasperNL]

With the INPUT 1 jack (image 1) the RF attenuation is set manual to 0dBm.
With the INPUT 2 jack (image 2) the manual RF attenuation can't be selected by the user. AUTO is the default when using INPUT 2.

This is also the case when in tracking mode. AUTO is the default.

[JasperNL]

I received an email from an EEVblog member/visitor. He owns the CMS54. More options and higher spec but comparable.
He did the following test on his unit.

Source: 0dBm 10MHz with 30dB attenuator on the input.
Both inputs measures the same power level. What you would expect.



My CMS50 input 2 is definitely damaged 

[tautech]

It seems you might get it very cheap then? 

[JasperNL]

I think i found the problem
The first amplifier in the input 2 path is faulty. When i bypass this amplifier the signal level goes up.
It is N317. Does anybody know what type it is?

[tautech]

Have you checked all the passive components close by?
In a recent thread for a SA fix a fusible resistor was open that was incorporated in the design to protect the input stages.
Lets hope somebody can recognise your 4 terminal smd marked "1" device.

[rastro]

Possible candidates:
 http://www.minicircuits.com/pdfs/ERA-1+.pdf
http://www.minicircuits.com/pdfs/MAR-1+.pdf (probably closer to 1GHZ range)

On the mmic amps it may be helpful to look what voltage and bias resistors are being used and then compare it to the recommended supply voltage/bias resistors in the data sheet. 

[Marcel]

First amplifier input 2 (red in the CMS52 service manual) 1NA03184

[KJDS]

First amplifier input 2 (CMS52) 1NA03184

I'd guess that should be INA03184

[JasperNL]

Marcel send me some schematics of the CMS52 input board. Thanks for that
Unfortunately is does not match my CMS50 input board. But I think is worth a try to replace the faulty part with an INA03184.

[JasperNL]

Received two INA03184. First thing i noticed is that the package is twice as small as the original one. It is not the correct part but I tried it anyway.
The signal level is now 10dB higher than it is supposed to be. So the MMIC was definitely faulty.
The INA has 25dB gain. That means the original one had about 15dB gain.
The search continues....
 

[Fraser]

From memory one of the Minicircuits MAR series had something close to 15dB gain.

The MAR-1 looks a possibility

When I see a 4 pin package like that with a single number between 1 and 8 on it, I think MAR or ERA series. MAR predates ERA and is a larger package.

I have attached datasheets and a useful document that details the markings etc.

[KJDS]

One minor word of warning, and my memory is a little hazy on the details, but once upon a time the original MAR series amplifiers were GaAs devices. IIRC, it was Avantek who upgraded their line to an InGaP process and used this upgraded process to make amplifiers with the same specification. Whilst the spec stayed the same, the gain, instead of falling gracefully above the max spec'd frequency carried on halfway to daylight. When used as replacements in many circuits they oscillated.

To keep things obvious to all, the new advanced devices were given the name of the previous ones and the old devices were renamed. I wonder if any of the other RF guys on here remember the details more clearly than I. The change took place around 2001 I believe.

[Fraser]

@KJDS,

Interesting information. Thank you 

I have used MAR series amplifiers for many years because they are stated as unconditionally stable (except for the MAR-8) and tend to be well behaved in most situations. I was not aware of the change that you mention but it is definitely something I will watch out for in future.

I personally love the small MMIC gain blocks as they are so easy to use and provide very respectable performance for their cost. I have used better MMIC amplifiers with a flatter response but the cost increases significantly with better flatness of response.

They are certainly better than the old Philips OM series hybrid amplifiers that I used to use.

Aurora

[rastro]

Aurora,

Thanks for posting "MMICs markings.pdf" -  this is a really handy cross-reference/identification sheet.

[JasperNL]

Still no luck finding the service manual for the CMS50.
Does anybody have any idea where i can find or buy the service manual?
 

[merox]

Still no luck finding the service manual for the CMS50.
Does anybody have any idea where i can find or buy the service manual?

Have you already tried calling Rhode & Schwarz for a manual? I've read many repair stories on http://www.amplifier.cd (german site) and the support was always described as very helpful. Sometimes they even switch you through to the former developer of the defective hardware and they seem to have been always very willing to help in troubleshooting.

[JasperNL]

Thanks merox for the tip.
I emailed R&S about the identification of the the part. They responded the next day with the partnumber:

MSA-0104

Never thought company's like R&S support the hobbyist with their old gear.

Rohde & Schwarz THANKS!!


 

[merox]

Never thought company's like R&S support the hobbyist with their old gear.

Well, as we say in germany: "It doesn't hurt to ask!" (Fragen kostet nichts!)

And it seems the part is cheaply available at ebay.

[Fraser]

MSA0104 is equivalent in spec to a Mini-Circuits MAR1. The MMIC shown in your picture has the markings of a MAR-1 component. No issue which is used but interesting all the same 

Aurora

[sorenkir]

Hi,
I had 2 MMICs "fixed" by simply heating them (quite a lot, in an attempt of desoldering them): one MAR-8 (in a Rohde Schwarz SMX) and a MWA-230 (in a Wavetek 5155A).
I don't know why (I don't think it was a solder joint problem), but maybe worth a try ?
Michel.

[JasperNL]

Replaced the MMIC wih MSA0104 and its working again
Levels are now correct. Maybe it needs calibration but for now i am very happy.
Thanks for all your input.

[tautech]

Replaced the MMIC wih MSA0104 and its working again
Levels are now correct. Maybe it needs calibration but for now i am very happy.
Thanks for all your input.

 
Merry Christmas