Author Topic: RFM69HW 433 MHz - Issue: low signal, returned RSSI value -105  (Read 881 times)

RazvanBiro

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Hello everyone,

I am using the RFM69HW module (and RFM69 library) for a new project I'm working on (first experience with this 433 MHz modules). I have sending/receiving problems due to low signal. The RSSI is on  both ends between -105 to -90 dBm.

Test setup for both end devices:
- RFM69HW 433Mhz with wire antenna 1/4 lambda (173 mm).
- my RFM breakout board with 47uF capacitor (simple board used to connect the 2.0 mm spaced pins to typically 2.54 mm space pinhead for Arduino). The antenna pin left out. The wire is connected directly to the RFM.
- Arduino Pro Mini 3.3V (with no led's and no voltage regulator).
- FTDI breakout board 3.3V - used for debugging and power up the arduino and transceiver.
 
The distance between the transceivers is about 1 - 1.5 meters.

In order to be shure that I am not doing something wrong, I used the Struct_receive/Struct_send examples from https://github.com/LowPowerLab/RFM69/tree/master/Examples, slightly modified the code for different test cases:

Case 1: Code as github.
   Struct_receive: RSSI between -105 to -90
   Struct_send: RSSI between -105 to -90
   
   I tried also with more than 10m distance and through 1 wall, transceiver is losing messages but the RSSI remains the same.
   
Case 2: IS_RFM69HW_HCW line commented out on both ends
   Struct_receive: RSSI of -85 to -77
   Struct_send: RSSI of -85 to -76
   
   Both ends lose a lot of messages. Maybe 2 from 10 (20%) of the messages were received.
   
Case 3: IS_RFM69HW_HCW line commented out on only on Struct_receive
   Struct_receive: RSSI of -22  to -28
   Struct_send: RSSI of -105 (time to time)
   
   Struct_Send does not receive the ack that the messages have arrived (console message: "...nothing...")
   
Case 4: IS_RFM69HW_HCW line commented out on only on Struct_send
   Struct_receive: does not receive anything
   Struct_send: does not receive ack
   
I have also tried all the cases with 2 new transceivers, 4 transceivers in rotation (each one tested with each other), wire antenna both 173 and 165 mm long, also tried both ends powered over power supply (in case of current issues)...

Does someone experienced the same thing?
Is there something I am doing wrong?
Can it happen that, if the seller sent me the RFM69W and leave the definition IS_RFM69HW_HCW uncommented the transceiver will get damaged?
I have also attached one image of the RFM69 I have...

Can someone help me with this issue?

Thanks!



Felix

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Re: RFM69HW 433 MHz - Issue: low signal, returned RSSI value -105
« Reply #1 on: June 09, 2017, 10:16:26 AM »
Razvan,
You have HW modules, you must enable the IS_RFM69HW_HCW setting.
You should also add more GND plane to your antenna. Solder a perpendicular wire to the GND pad next to the antenna pad (same length).

RazvanBiro

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Re: RFM69HW 433 MHz - Issue: low signal, returned RSSI value -105
« Reply #2 on: June 09, 2017, 12:26:58 PM »
Hi Felix,

I tried id,.. but it didn't work . :(

I also removed my breakout board and solder the wires and the 10uF cap directly to the pins. (see attached image 1).

Attached are the results:

Felix

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Re: RFM69HW 433 MHz - Issue: low signal, returned RSSI value -105
« Reply #3 on: June 09, 2017, 01:54:08 PM »
Well .. not sure what else to suggest, short of starting with something that is known to work :)
Like .. a Moteino :)

onewhotriedit

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Re: RFM69HW 433 MHz - Issue: low signal, returned RSSI value -105
« Reply #4 on: December 28, 2018, 01:19:26 PM »
Hi alltogether,

I had the same problem and solved it as follow.
I found out that the bitrate directly influences the signal range. In the "initialize"- function is a bitrate of 55555 baud set as default.
The solution may be a change of RFM69.cpp with a lower bitrate, or an additional setting of bitrate within the Setup-function (after initialisation)
Because I am reluctant to change the library, I added following lines to my sketch:

Code: [Select]
#include <RFM69registers.h> // Include- block, needed for recognition of REG_BITRATEMSB / REG_BITRATELSB

radio.writeReg(REG_BITRATEMSB, RF_BITRATEMSB_1200); // setup- function, after radio.initialize(...)
radio.writeReg(REG_BITRATELSB, RF_BITRATELSB_1200);   // setup- function, after radio.initialize(...)

With this changes I have RSSI-Values of about -30 with 1m between sender and receiver, timewise under -30
Other possible values are 2400, 4800, 9600 and more (all listed in RFM69registers.h)
With 1200 I had to set the timeout of sendwithretry() higher (I believe its default value is 50ms) With 200ms it seems to work.

Hope it helps.