Low TX power with Feather 32U4 RFM69

[akcnc]

Hello,

I have two Feather 32U4 with 900 MHz RFM69 transceivers (Product ID: 3076) that are not transmitting with the programmed power. Is it possible to exchange or otherwise replace these units? They are from order #2905573 on 8/19/22.

I did not do anything that would damage these transceiver modules like using them without antennae and took ESD precautions. They do transmit but I found excessive packet loss compared to other units which led to pulling out the spectrum analyzer. Signal strength was compared using a reference antenna on the spectrum analyzer and same firmware/hardware setup.

Here's the output from a functioning unit:

Upper line shows max value

FPADAPT1_resized.jpg (248.71 KiB) Viewed 73 times

and here is the output of one of the two weak units at the same settings:

Upper line shows max value

FPADAPT7_resized.jpg (260.99 KiB) Viewed 73 times

[adafruit_support_mike]

They are from order #2905573 on 8/19/22.

That's past our 30-day return/replace period. I'm sorry.

Try changing the transmission power settings and see if that has any effect on the output.

[akcnc]

Try changing the transmission power settings and see if that has any effect on the output.

Alright, I tried adjusting the power settings on a bad unit and compared directly to a good unit. It is set to continuous mode, FSK, no frequency deviation to get unmodulated carrier, and 9600 baud. The rest of the setup is the same.

This is max hold on a good unit reaching around -39 dBm and one of the weak units showing -60 dBm. The good unit had power programmed to +0 dBm while the bad unit was set to +20 dBm.

Max hold of good unit vs bad unit

0dbmgood_20dbmbad_resized.jpg (245.02 KiB) Viewed 53 times

I also tried resoldering the antenna to see if it was a bad connection there causing problems. No luck there.

[adafruit_support_mike]

That does look like the board has low transmission power.

If you'd reported it during the 30-day return/replace period, I would have been able to authorize a replacement. At this point, I'm afraid I don't have any service options.