3 ms·

Semi-educated guess: 802.11 is a spread-spectrum signal, where you take your information, and use it to modulate a much faster "noise" signal. (Which is then us

Semi-educated guess: 802.11 is a spread-spectrum signal, where you take your information, and use it to modulate a much faster "noise" signal. (Which is then used to modulate the carrier wave) https://en.m.wikipedia.org/wiki/Direct-sequence_spread_spectrum https://en.m.wikipedia.org/wiki/Direct-sequence_spread_spect... My guess is that by underclocking the PLL, you are slowing down to pseudo-noise signal, so it will have a narrower bandwidth. The 2.4 GHz carrier is generated separately, so is unaffected by lowering this clock. The overall effect would be that your RF signal is still centered in the same carrier, but the signal looks narrower.

makomk 8y ago
Almost. As I understand it, most 802.11 hardware works by creating a baseband I/Q signal with the center frequency at 0 Hz using a pair of DACs and then upconverting it to the final transmission frequency by multiplying it with a seperately-generated carrier frequency. (The idea of negative frequencies may seem a bit strange, but because there are seperate in-phase and quadrature components the math works out.) If you decrease the DAC clock but keep the carrier the same this is what happens.
leetbulb 8y ago
Yeah the ESP8266 has two separate PLLs (RFPLL and BBPLL)[0]. The RFPLL generates the carrier on 2.4GHz. They specifically under clocked the BBPLL[1][2], which is the clock the CPU uses and ultimately what modulates the RF carrier. 0: http://www.danielcasner.org/wp-content/uploads/2015/08/esp8266-decapped.png http://www.danielcasner.org/wp-content/uploads/2015/08/esp82... 1: https://github.com/cnlohr/nosdk8266/blob/master/src/nosdk8266.c https://github.com/cnlohr/nosdk8266/blob/master/src/nosdk826... 2: https://github.com/cnlohr/esp8266oddclock https://github.com/cnlohr/esp8266oddclock
ajb 8y ago
It's not spread-spectrum, but you are otherwise correct - the main point is that the carrier is generated separately. The modulation signal is slowed down, the carrier is not.
- TFortunato 8y ago
  Thanks for the correction! Been a while since I looked at wireless stuff, but on checking it was 802.11b that used DSSS, but newer 802.11 standards use different modulation techniques.

makomk 8y ago

Almost. As I understand it, most 802.11 hardware works by creating a baseband I/Q signal with the center frequency at 0 Hz using a pair of DACs and then upconverting it to the final transmission frequency by multiplying it with a seperately-generated carrier frequency. (The idea of negative frequencies may seem a bit strange, but because there are seperate in-phase and quadrature components the math works out.) If you decrease the DAC clock but keep the carrier the same this is what happens.

leetbulb 8y ago

Yeah the ESP8266 has two separate PLLs (RFPLL and BBPLL)[0]. The RFPLL generates the carrier on 2.4GHz. They specifically under clocked the BBPLL[1][2], which is the clock the CPU uses and ultimately what modulates the RF carrier. 0: http://www.danielcasner.org/wp-content/uploads/2015/08/esp8266-decapped.png http://www.danielcasner.org/wp-content/uploads/2015/08/esp82... 1: https://github.com/cnlohr/nosdk8266/blob/master/src/nosdk8266.c https://github.com/cnlohr/nosdk8266/blob/master/src/nosdk826... 2: https://github.com/cnlohr/esp8266oddclock https://github.com/cnlohr/esp8266oddclock

ajb 8y ago

It's not spread-spectrum, but you are otherwise correct - the main point is that the carrier is generated separately. The modulation signal is slowed down, the carrier is not.

TFortunato 8y ago
Thanks for the correction! Been a while since I looked at wireless stuff, but on checking it was 802.11b that used DSSS, but newer 802.11 standards use different modulation techniques.