CC1120: RSSI differences between TRXEB and CC1120EM-420-470 and my custom daughter card

It's not clear:

The daughter boards (containing the CC1120) you are testing are custom, it's only the mother board (containing the MCU) that is different?

--

Do you use the same type of antenna in all tests?  

Same antenna on all.  Our custom board with the CC1120 is the same for TX and RX.  No MCU on those.  Our RX motherboard and TX motherboard are custom which connects to a CC1120 board.  Almost in the same way it's done with the TrxEB board.

Hi Sutton,

Could you share your schematic and layout so that I can take a look?

Regards,

HG

5611.160-4020A2.pdf160-4020A2_layout.pdf

Sure.  Here are the files.  These have been uploaded on various other posts earlier for other non-related troubleshooting issues, and other techs said they looked good.  But, have a look.

I also have produced this testing grid.  I have 4 custom TX/RX boards and 1 TrxEB (the other is damaged until I get another one soon).  If I put the custom boards in various configurations, these are the results.  For example, when board #1 is a TX and the the others are used as a RX along with the TrxEB, those numbers are the dB results of receiving the TX packet.  Note that #2 isn't there.  It is a damaged board.  #3 as a TX or RX looks to be a problem, for sure.  But, not sure what that means.  And, #1, 4, and 5 seem to be transmitting well to the TrxEB, but not among each other as well.  So, I was looking for answers on why.

RSSITestGrid.pdf

So basically different mother boards containing MCU gives different RSSI with the same RX and T boards? 

Typically issues like this are caused by frequency offset and antenna detuning. But since the RX and TX boards are the same for all tests it's not offset and if you use the same antennas in all test it shouldn't be an antenna issue.

Is the SPI interface for some reason active (clocked) when you receive? 

The SPI bus is turned off when the RX is waiting for a packet (External Interrupt).  We bought some antennas specifically tuned to 433Mhz.  Closest we could get to 434Mhz.  So, each TX and RX board (#1-#5) each have its own antenna.  See example of board #3.

Hi Sutton,

Could you try the following and post the result here:

Transmit with TrBEx1 and receive with your custom boards.

Do the tests that you have done conducted instead of with an antenna.

Measure the output power from your device with a spectrum analyzer conducted.

Regards,

HG

In addition to the above:

- Check the frequency offset

- Have you verified that the TX power is s expected? (conducted measurements, good and bad RSSI combination)

- Could you post a picture of the full setup? Eq daughter board on mother board with the combination that gives good RSSI and poor RSSI.  

TX/RX RSSI Testing (dB)


				RX

		1	2	3	4	5	6	TrBEx1(2631)	TrxEB2

TX


1		X		-65	-40	-65		-27


2			X

	
3		-80		 X	-75	-90		-60


4		-45		-50	X	-50		-25


5		-45		-55	-45	 X		-27


6							X



TrxEB1		-50		-60	-45	-75		 X


TrxEB2										X

TrxEB tests.  I have a 2nd board on order.  2nd board USB failed.  I am in the process of doing some output measurements from the various tests.

pics of my setup 2 RX pics (display), 2 TX pics (3V Duracell battery), and pic of TX/RX boards.  RX/TX boards plugged into either RX or TX as a daughter card.