ESP32 Based SDR Transmitter - Part 4 Transmitter on the Air

In this video I get the transmitter on the air and test the output in the lab and hear the output using a PA based websdr.org endpoint.
Part 1 - • ESP32 Based SDR Transm...
Part 2 - • ESP32 Based SDR Transm...
Part 3 - • ESP32 Based SDR Transm...
LPF board
github.com/thaaraak/lpf
RF Tools Filter designer
rf-tools.com/lc-filter/
The ltspice file I was using
github.com/thaaraak/ltspice/b...
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

[@alexandrvalentinovich164]

Good result, thanks, Ian! R9OFG, 73!

[@jburchm1]

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

[@na5y]

Thank you Jonathan - scope off in the mail today!

[@Masirah1]

Excellent video. I like that you showed everything.

[@na5y]

Glad you like the video - thank you for the comment

[@khimbittle7705]

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

[@na5y]

Thank you Khim - glad you enjoyed!

[@rfdave3980]

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.

[@na5y]

Thank you for the kind comments. Definitely looking forward to the next video - in particular the audio switching. The RF switching I'll do with relays but the audio switching I might be doing with either an FST3253 or a dedicated audio switch like the older CD4052

[@rfdave3980]

@@na5y Will you use two FST3253, one for transmit and the other for receive? I plan on using two, line out 2 for TX Quad and line in 2 for RX Quad. Line in 1 for Microphone Line out 1 for Speaker Amp .

[@na5y]

@@rfdave3980 Exactly what I had planned

[@johnwest7993]

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. :)

[@na5y]

I like your way of thinking ;)

[@andrethomas1800]

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

[@na5y]

Thank you Andre for the clear up on harmonic enumeration!

[@vk2ycj]

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.

[@na5y]

Thank you Jamie. I might have mentioned this before but I went to Primary and High School in Beresfield. A small world indeed!

[@vk2ycj]

Yep, yep, one of the boys at the radio club told me you lived in the Newcastle area in the past.

[@R2AUK]

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!

[@na5y]

Thank you Alex - I definitely think being able to adjust the decoupling cap is the way to go!

[@123risu]

Great project 👍 New year greetings!

[@na5y]

Thank you - and a happy new year to you also!

[@4youian]

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

[@4youian]

PS, a little trick in ltspice is to set the AC signal to 2 (instead of 1) so it adds 6dB to the graph.

[@na5y]

@@4youian Hah - nice trick. Happy New Year to you too Ian!

[@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.

[@pjmccracken]

I am guessing you can do either method as shown between 11 and 13 minutes in this video ?

[@na5y]

@@pjmccracken Thank you for the kind comments Peter. Here's where I got the idea for the bifilar + separate: www.wb5rvz.org/ensemble_rxtx/09_qse Look down the page for transformer T2. Let me know if this makes sense - its simpler than it sounds ;) You simply wind the bifilar 11T and then wind the single winding over the top of that

[@na5y]

@@pjmccracken I actually wound one in this old video kzbin.info/www/bejne/baqVenutq7poqas starting at 01:58

[@antaf56]

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

[@na5y]

I believe the calculation on toroids.info is based on covering the toroid approx 90% of the circumference. How bunched up did you have the 16 turns? You really don't need to leave any space for the secondary - you can simply wind over the top of the primary if you like. Have a great new year yourself Antonio and thank you for the comment!