Electronics > Repair
CMU200 Rx level issue / failed loop test
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Sas:

--- Quote from: _Wim_ on January 24, 2022, 09:34:59 pm ---Congratulations. Looks very good! Can you post a picture how you installed the BHD filter?

--- End quote ---
I soldered the same, isolated with Kapton tape. I removed the solder mask and added a GND solder pad (PB tin) under the filter on pcb (i marked the size and location in the photo). I soldered the filter with hot air, then soldered the top of the filter to ground and the in / out connection with a soldering iron (new toy on board JBC CDE-2BQA  ;D ;D ;D ).

The waveforms look similar, my deviation from +0.7 dB to -1.2 dB. My gain drop is more linear. If you have a problem, it may be possible to correct it with an attenuator (I think 6 dB, I marked in the photo).
It will not change the fact that you may have too low gain (from -0.1 dB to -1.4 dB) in the whole spectrum analyzer operating range or too low signal generator level. I don't know why. Spectrum analyzer gain too low or generator RF level too low. Missing +0.8 dB gain (or generator RF level) causes errors from loop test 1-> 4 / 3-> 2. May require calibration or some repair.
_Wim_:

--- Quote from: Sas on January 25, 2022, 09:18:33 am ---I soldered the same, isolated with Kapton tape. I removed the solder mask and added a GND solder pad (PB tin) under the filter on pcb (i marked the size and location in the photo). I soldered the filter with hot air, then soldered the top of the filter to ground and the in / out connection with a soldering iron (new toy on board JBC CDE-2BQA  ;D ;D ;D ).

The waveforms look similar, my deviation from +0.7 dB to -1.2 dB. My gain drop is more linear. If you have a problem, it may be possible to correct it with an attenuator (I think 6 dB, I marked in the photo).
It will not change the fact that you may have too low gain (from -0.1 dB to -1.4 dB) in the whole spectrum analyzer operating range or too low signal generator level. I don't know why. Spectrum analyzer gain too low or generator RF level too low. Missing +0.8 dB gain (or generator RF level) causes errors from loop test 1-> 4 / 3-> 2. May require calibration or some repair.

--- End quote ---

Thanks for the additional info and pictures. Maybe I will experiment a bit more with the filter placement in the future, but for now I am quite satisfied how it works. Nice JBC you have there, makes my JBC BT-2BWA look "old fashioned"  :)
Bravo:
I found some filters on Arrow electronics website. They are smaller than the originals but have the correct spec.
So some kapton tape & thin wire will be required.
They are discontinued & very cheap. They have large stocks ............until throw them out.
The 836.5 Mhz one has a  part No B39841B4147U410  @ $0.45 for one.
The 1842.5 Mhz one has a part No SF1192B  @ $0.73 for one.
Bravo:
I ordered some filters from 
https://www.ectransistors.com/10-PCS-INDUCTOR-TRANSFORMER-MMCL-DFC3R836P025BHD-3R836P025-DFC3R836P025BH.html

After paying for them & courier shipping, they told me that the price had gone up 500%, so I payed the extra. They then shipped the filters by economy post. Assuming the packet is not empty, they are still cheaper than the ones on Ebay, but you have to buy 10.   >:D
Bravo:
I fitted the small 836Mhz filters from Arrow,  part No B39841B4147U410. They work fine.
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