ESP32 Based SDR Transmitter - Part 4 Transmitter on the Air

LPF board

RF Tools Filter designer

The ltspice file I was using

0:00 Intro
0:59 Designing the filters using rf-tools
2:45 Looking at the lowpass filter in ltspice
4:29 Looking at filter input impedance
6:13 Looking at the filter on the spectrum analyzer
7:34 Looking at a 14 MHz bandpass filter in ltspice
9:07 14 MHz BPF on spectrum analyzer
9:51 A bit of a diversion into toroid winding and the effects...
13:28 Testing setup
15:10 Single tone on oscilloscope
16:05 Two tone test
16:57 Single tone on spectrum analyzer
18:28 Two tone on spectrum analyzer
20:04 Changed to 7 Mhz - confirming that LPF is removing harmonics
21:21 Finally transmitting. Results received by K3FEF websdr endpoint
22:39 Wrap up and next steps

[rfdave]

Great Video Ian. Sad to see this series at the end, but excited to watch for the next plan series. I have enjoyed following your videos. Also enjoyed write code for some features and learning and tinkering with Tayloe detector. Love it.

[jburchm]

Thank you for showing the filter construction process. I always find them fascinating. Sorry to hear about your scope!

[vkycj]

Fantastic video Ian. I have really enjoyed the SDR series - especially the testing and verification with Spectrum Analyser and Oscilloscope. Cheers, Jamie, VK2YCJ, Newcastle, Australia.

[andrethomas]

Great video as always! With awesome results! To answer your question on 1st or 2nd harmonic - The fundamental is the same thing as the first harmonic... so the unwanted ones are 2nd, 3rd etc

[mikehibbett]

Brilliant analysis on the coils, thanks

[khimbittle]

Great video, I really enjoy all of the SDR experiments, I am trying this same technology on my RC transmitters/receivers.

[RAUK]

Great project! Personally I ended up using yet another tuning capacitor in double-tuned circuit the one that tunes the coupling. Gives an extra degree of freedom. 73s and HNY!

[Masirah]

Excellent video. I like that you showed everything.

[johnwest]

I've found it's always better to have a 4-channel 'scope so you can blow up 2 of them and still be able to look at 2 channels. I use them sort of like spare tires. :)

[youian]

Thanks Ian for another very interesting video. Happy New Year. Looking forward to some great content in the new year. Sounds very interesting! This series has been enormously useful and will be a great reference. Cheers, 73, VK7IAN

[antaf]

Thanks for the great videos Ian!! Just a question, looking to the filter toroids in the previous video I found that the indicated value for the inductance is quite different from theoretical one calculated for Amidon cores, for example, for 10m the indicated inductance is 1.40uH with 16 turns on T37-6, by computation I found 0.77uH. Is, in your opinion, this difference due to the (primary) winding all bunched to leave room for the other (secondary) winding, as you clearly explain in this video? Many thanks, and have a wonderful new year. Antonio, IW0FCI

[alexandrvalentinovich]

Good result, thanks, Ian!
R9OFG, 73!

[pjmccracken]

Thanks for this series Ian, I really enjoyed it ! I have wound plenty of trifilar transformers but never done a bifilar plus separate winding, any chance you could give a brief explanation of how this is done and/or a very short video on it ? I've scoured youtube but failed to find anything useful.