Software Defined Radio (SDR) Experiment Board

RE: Software Defined Radio (SDR) Experiment Board

Fruitpunch12 — Tue, 16 Dec 2025 01:39:04 GMT

Hi Shabaz, thank you for the schematic since I am new to RF and hobby radio I have a few questions about the schematic design. First I see you used a 7805 voltage regulator for the power source, can I make my own voltage regulator with power mosfets to preform the same function? I also see you said you used a sd5400 which is quad n channel fet array. I also wanted to ask if I can use something like 4 RFP30N06LE's in parallel. I read that I could replace the dual channel op amp for something else so I might try a design with an NE5532 or TDA2822 in kicad.

I'm just using your schematics as a template for a quadrature demodulator and wanted to know if some of these changes make sense with what your original plan with this project was since I am new to RF circuits as a whole. I plan on using this design for a SDR based transceiver using a teensy 4.1 micro controller for the ADC conversion and I/Q signal processing since I've seen some projects already using it for an SDR set up. Just wanted to ask some of those questions.

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Sun, 03 Dec 2023 12:44:56 GMT

SDR trolling is a thing now:

Source: https://youtu.be/h-fKtt7nRSg?si=UprlB7hwqozUFfD3

RE: Software Defined Radio (SDR) Experiment Board

Observer — Wed, 08 Jun 2022 17:55:15 GMT

I am a QSD fanatic !

From where I can buy the board?

Also, can the 7474 be configured as a simple squarewave driver to the mixer ?

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Sun, 17 Oct 2021 20:23:25 GMT

[View:https://players.brightcove.net/1362235890001/NkxiVJdjx_default/index.html?videoId=6277585064001:740:466]

Note to self: FPGA design quadrature_oscillator_advanced

bypass quad generator, get clock at PMODB[0]

Clocks.fclk0_mhz = 100

oscillator_register.write(0x0, 18)

RE: Software Defined Radio (SDR) Experiment Board

rsjawale24 — Sun, 17 Oct 2021 07:09:31 GMT

This is an interesting project. This got me thinking. How to make a SDR that can send data to PC using USB so that it can be used with GNU radio? I have no knowledge about drivers so that the custom SDR could be detected by GNU radio

RE: Software Defined Radio (SDR) Experiment Board

shabaz — Sun, 17 Oct 2021 02:12:56 GMT

This took quite a few evenings! a lot longer than expected, but finally I have a functioning frequency synth, it uses an off-the-shelf Si5351A board, and a Pi Pico, plus rotary encoder and display.

Now the dilemma, should this synthesizer be a separate PCB, or should the SDR Experiment Board be modified and physically extended (say twice the size, I want to space things out).

Here it is receiving a French radio station (I still need to change the code so that the displayed frequency is 1/4 of the generated signal, and compensate for offset set in the PC SDR software).

Keeping with the experimenter theme, this is using Python on the Pi Pico so that code can be easily modified, and the ready-made Si5351A board means no tiny parts to solder.

The Si5351a board in the photo is an Adafruit model, but lower-cost boards from China are compatible too (I tried it). That's important, because the Si5351A chip is becoming hard to find due to the semiconductor shortages, whereas the China version is using a different chip (which happens to be compatible) which hopefully remains available.

[View:/resized-image/__size/883x552/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/2146.contentimage_5F00_216647.jpg:883:552]

[View:/resized-image/__size/656x412/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/0083.contentimage_5F00_216648.jpg:656:412]

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Fri, 01 Oct 2021 18:08:16 GMT

Radio China International

7.35292 MHz, AM, 8 KHz bandwidth, 12.9K as midpoint, Youssef filter because [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/4075.contentimage_5F00_1.png:16:16]

[View:https://players.brightcove.net/1362235890001/NkxiVJdjx_default/index.html?videoId=6275113863001:740:466]

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Fri, 01 Oct 2021 13:12:03 GMT

I've temporary replaced the local oscillator by this FPGA design. It allows me to scan the frequency range automatically.

[View:https://players.brightcove.net/1362235890001/NkxiVJdjx_default/index.html?videoId=6275072946001:740:466]

[View:/resized-image/__size/620x301/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/0456.contentimage_5F00_216553.png:620:301]

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Thu, 30 Sep 2021 19:36:42 GMT

Nothing yet, but searching ...

[View:https://www.youtube.com/watch?v=s6ebdXs1rvA:1110:699]

The circuit definitely works.

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Thu, 30 Sep 2021 18:18:21 GMT

Workaround for the wrong jack plug that I ordered:

[View:/resized-image/__size/437x900/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/contentimage_5F00_216544.png:437:900]

This will do for the time being. I had this cut-off stereo cable here since ages. Finally it does some service.

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Thu, 30 Sep 2021 16:25:43 GMT

The RF amplifier:

[View:/resized-image/__size/620x194/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/8863.contentimage_5F00_216543.png:620:194]

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Thu, 30 Sep 2021 12:19:35 GMT

Two views of T1

[View:/resized-image/__size/620x273/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/3173.contentimage_5F00_216541.png:620:273]

I ordered a PWB-4-ALBPWB-4-ALB.

Measurements from the datasheet: (they use 130 KHz)

[View:/resized-image/__size/620x119/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/7367.contentimage_5F00_216542.png:620:119]

My measurements with the component not soldered, at 100 KHz (max frexuency of my meter)

L: primary 44.5 µH, secondary 185.3 µH

D: primary 0.14, secondary 0.19

RE: Software Defined Radio (SDR) Experiment Board

Jan Cumps — Sun, 26 Sep 2021 11:26:55 GMT

The IF Amp is finished

[View:/resized-image/__size/562x900/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/7288.contentimage_5F00_212005.png:562:900]

[View:/resized-image/__size/618x380/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/6082.contentimage_5F00_212006.png:618:380]

All fitted well except the jack socket.

According to the label, it matches the BOM: No it doesn't. My order has a 1503 02 - I checked, and I made the mistake when ordering this part.

[View:/resized-image/__size/620x408/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/2330.contentimage_5F00_212007.png:620:408]

Physically, the footprint is different. The pads are OK, but the 2 pins don't fit the holes.

They are at a different position and farther apart, with a 3rd central at the end.

[View:/resized-image/__size/360x300/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/3010.contentimage_5F00_212008.png:360:300]

It wasn't hard to get things to fit. Mechanic force is on the pads now, so I'll have to be careful when (un)plugging..

edit: I checked both datasheets and the pinouts aren't compatible.

I removed it. Luckily without damage. It's good to practice the rework muscles.

[View:/resized-image/__size/620x321/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/3823.contentimage_5F00_212009.png:620:321]

I don't know what i'll do next - build an adapter or purchase the right connector.

RE: Software Defined Radio (SDR) Experiment Board

shabaz — Sat, 25 Sep 2021 17:38:02 GMT

A first experiment of sorts.. what happens when there is no IQ output.

Here is the testbed; the I/Q output can be simply disabled by setting the Q output to zero (just disconnect the indicated jumper):

[View:/resized-image/__size/620x436/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/1220.contentimage_5F00_212004.jpg:620:436]

Next, a radio station is tuned in by adjusting the frequency from the signal generator. As the frequency is adjusted, the spectrum, amplitudes, and the waterfall view can be observed, and compared with the result when the jumper is re-inserted.

RE: Software Defined Radio (SDR) Experiment Board

shabaz — Sat, 25 Sep 2021 14:46:20 GMT

I finally soldered up the board, and started troubleshooting it. Finally, it does seem to work, although I had to connect the antenna to the RF Amplifier input, instead of the filter.. not sure why but that didn't function, I'll attach test equipment to it later. Anyway, I was successfully able to hear the AM broadcast band with SDR Sharp software, with the antenna wire attached as shown in the photo below.

[View:/resized-image/__size/755x418/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/1220.contentimage_5F00_211996.jpg:755:418]

However, to get the board working this far, there is a fix that needs to be done, because there's an issue on the board that prevents quadrature signals being generated : (

The problem is, pin 12 in the circuit diagram here should be connected to pin 5, but was incorrectly connected to pin 6.

[View:/resized-image/__size/538x355/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/8176.contentimage_5F00_211997.png:538:355]

I've updated the blog post with the corrected circuit diagram, and an explanation how to fix it on the board. In brief, pin 12 of U1 needs to be lifted (or the trace leading up to it can be cut) and then that IC's pin 12 needs to be wired to pin 5. The other wire visible in this photo is the fix for the issue Jan discovered earlier (it will still work without that fix, but is needed if the quadrature signals are desired to be isolated using jumpers as shown in the photo). Both fixes are in the blog post section Revision 1 PCB Issues and Fixes and will be resolved in a Revision 2 board.

There's actually another issue which is benign normally, but needs some care if the jumpers are removed. Basically, resistors R4-R7 end up being disconnected from the SD5400 IC, which leaves then floating and not great for a bit of ESD protection.

The revision 2 board will move the resistors R4-R7 to the other side of the jumpers in the photo, and also improve the silkscreen in a few areas, and will be slightly easier to solder. However, for now, if anyone wants to use the Rev 1 board, then the pin 12 issue needs the fix as shown in the photo in red, and the other fixes are only for users who want to isolate connections to (say) add their own circuitry.

[View:/resized-image/__size/773x433/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3d95cdde-5ebc-4fdd-803b-cb3caeff70ed/1205.contentimage_5F00_211998.jpg:773:433]