ESP8266 Community Forum

- Wed Oct 22, 2014 7:39 am #1828 it could be your 50 ohm line like squonk said? the thicknes is not 25-26mill all the way to the connector. looks like lots of reflections there

My analogue knowledge is very very rusty so please dont take it serious

- Wed Oct 22, 2014 8:09 am #1831

it could be your 50 ohm line like squonk said? the thicknes is not 25-26mill all the way to the connector. looks like lots of reflections there

Hmm not sure , even when the full RF power is reflected due to a bit of mismatch (approx 86Ohm @10mil vs 50Ohm @26mil , still terminated with a solid 50.0Z in my SA) , I still don't see how the BW could 'explode' like in the first pic.
Further the mismatch is still present when I did the second measurement with the ESP powered off , but the occupied BW of my AP looks good.

I also tried to put an 10dB attentuator on the RF-In of the SA (SA goes only up to +20dBm), same spectrum but 10dB lower. So definitely no distortion effect of the SA input stage here.

- Fri Oct 24, 2014 1:43 am #1885 I did some further testing , especially for ruling out that the impendance mismatch of the SMA feedline influences the measured spectrum.

For that I first checked if the RF Power of the ESP is within the range written in the ESP8266EX Datasheet.
I used a Minicircuits ZX47-40-S+ Power Detector (I'm too cheap for the Power Detector Head for the SA...)

Thats the output voltage vs RF input Power diagram of the Minicircuits Powerdetector



And that is what I measure



The ESP Datasheet states a output Power of +15.5 to +17.5dBm @ 72Mbps , my AP says the ESP is associated with 65Mbps




So I get roundabout +16dBm out of the ESP , but one have also have to take the RSMA to SMA Adapters and RF Cabling into account what I used to connect the Powerdetector to the ESP (~ -0.5dB) .
Well within the values in the Datasheet

I also did a S22 (aka 2 Port Insertion Loss measurement) on the 50 Ohm line between the RSMA connector and the 5.6pf coupling cap (the part of the PCB where I have a missmatch due to 10mils vs 26mils)




Doesn't look soooo bad afterall

- Fri Oct 24, 2014 10:28 am #1912 DOH!

Okay sometimes it is better to RTFM before doing things

It was indeed a distortion effect on the spectrum analyzer! I left the "High Gain" Option on in the settings menu.

Here is how the spectrum looks when all settings are correct



It's safe to say now that the ESP works on my breakout board as it should.
Compared to the leaked preliminary FCC test report I get similar results. YAY