Why Six Peaks?

joelindo · February 04, 2021, 12:20:18 PM

Spectrum analyzer picture of RFM69 transmitting at 915MHz. Why are there six peaks?

Felix · February 04, 2021, 12:23:01 PM

Maybe an explanation how and what you transmit, and also how you measure, would make it a real starting point for a discussion.

joelindo · February 04, 2021, 02:51:40 PM

I'm just trying to learn! . . . Here's the program that shows up on SDRSharp. The noise floor is between -60 and -65. Notice also that I'm not writing to the fifo, yet the tx sends a carrier. Registers are set to factroy before program runs either by hard reset, or pwr on reset.

import spidev
spi = spidev.SpiDev(0,0)
spi.max_speed_hz = 2000000
rx = spi.xfer([0x81,0x0c]) #address and data
spi.close()

joelindo · February 04, 2021, 02:53:47 PM

Also, carrier continues to emanate after program ends. Hard reset or switching to stby mode required to stop it.

Felix · February 05, 2021, 10:24:05 AM

Maybe if you used my library I could throw my 2 cents in here but I don't even know where to begin.
SDRSharp tells me nothing. Do you capture with an antenna, or straight from radio output?
Your photo shows no amplitudes. Just nothing much to talk about $:-\$

joelindo · February 05, 2021, 11:30:45 AM

I wish I gave it some thought before posting my last. Just figured out that 0x81 getting 0x0c is telling the transmitter to turn on.

joelindo · February 05, 2021, 11:35:28 AM

I have a Tektronix TDS 210 scope and the SDRSharp.

joelindo · February 07, 2021, 02:45:16 PM

Yea, it's antenna to antenna. . . I'm so far behind all of you that I don't know the appropriate questions to ask. I do have an idea to chase down. If my SDR spectrum analyzer is close to accurate about dB levels, I should be getting levels higher than -40dB with the default settings. I'll be back later, probably much later, with more intelligent questions.