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The new version solved the problem. I have it running now. Thank you Frank! Now I have to learn how to use Tisho's menu! I am embarrassed to say that I figured out the problem with the LO birdies and the problem was me. It turns out that the FFT mode in my new oscilloscope does not include an...

Interesting. Perhaps it is because I am using the 8mA setting on the Si5351 or have a termination problem. I am also running the LO through a length of coax - I may have an impedance mismatch. I will investigate later today. I too was alarmed at the temperature reading. But if I put my finger...

For the new software, I get this error compiling because the define is only called with HARDWARE_DO7JBH_T41 enabled. 73, Bill WH7U

Oh nice. Preselectors are great. I think a good set of filters plus a preselector might be a good idea. The only people who don't like preselectors are very lazy people :-) Thank you for updating the code. I am excited about Tisho's menu assistant and tuning steps and the bug fixes! I have not...

I think this is probably the best way to go. The narrow IF could have smaller integrating capacitors so a naturally narrower bandwidth. I know that this project was not meant to compete with the top end receivers out there. But you have built all the difficult pieces in DSP - the performance of...

Thank you Karlchen. I did not know wideband transformers were available.

Frank, you are a genius! I found that my Si5351 drive strength was set very low. I turned it up to 8mA and added a 50 Ohm resistor to my receiver and it came alive! It is working much better now and all the weird noise is gone. Thanks for the tip. In case anyone else might be having this...

On another subject, I wanted to see if I could make a transformer that covered from 100 kHz to 200 MHz for the input to a wide-band QSD. This is a very large bandwidth for one transformer. A 2-core transmission-line transformer can provide good unbalanced to balanced 50 Ohm to 200 Ohm very...

Hi Frank, Si5351 I think you are right. Thank you for the link - I reviewed it and also re-read the data sheet. When I get back to the radio, I will check to see that I have the setting at 8 mA. It sounds like I don't. IF: Youngblood explained the compromise in IF bandwidth in part 4 of his...

@DD4WH and everyone. I am not having great performance from my modified QRP Labs QSD receiver and Teensy setup. I finally bought myself an oscilloscope, an RF generator, a large pile of filters, a small pile of attenuators, and a step attenuator so I can do some actual testing to figure out what...

Mirror rejection is the same as image rejection. I think it is more of a DSP term than a radio term, but it means the same thing.

I didn't measure it yet. I need to get some more attenuators. I used to have a whole bunch of them but now I only have a few.

Nice work Tisho! Sounds like your radio is working well. I like the menu - it looks great.

Ok Frank. I figured out how to make complex bandpass filters. After fruitless research and less-fruitless experimentation, it is actually embarrassingly trivial. I don't know why this information is so hard to find. I can't find any good reference material on complex filters - just a bunch of...

I recreated the filter kernel in calc_cplx_FIR_coeffs in MATLAB and plotted the response. I see now how it is a Hilbert filter and Bandpass filter both. This is for 96 kHz sampling rate, decimation by 8, and an IF frequency of 24 kHz (that gets decimated down to 3 kHz). I set the bandwidth from...

@DD4WH Hi Frank, I read the chapter in my DSP book on FFT convolution. I don't have the Lyons book but I do have "Digital Signal Processing" by Steven W. Smith. I also have the standard Oppenheim/Schafer book you list in your references. Then I worked my way through the code. I think I...

Hey Frank. No problem on all the time it took. I'm learning and having fun with this stuff. I am planning to dig into this filtering business a bit more. It may take time because I have to juggle work/fun. I have been reading through the forum and getting up to speed, but I still don't have a...

hi Karlchen, I was trying to get the Potato chips from the Potato distributor listed on their website and the distributor told me they didn't have stock. I didn't know there was an online shop. I am going to order some! Thanks for the tip! The PA0RWE is a nice board. I like the simplicity of...

Hi Frank B, I checked again a little more carefully. At 256kHz sample rate, my S meter is almost at max with noise, so I didn't think it was working. But you are right. I can hear signals. I don't have any strong WFM stations near me so I tried it at 7MHz and the signals are there - I just can't...

Here is a link to MATLABs ARM code generator if you want to see what it is all about: https://www.mathworks.com/help/releases/R2018a/supportpkg/armcortexmdst/examples.html

@DD4WH Hi Frank, I spent way too much time fooling with MATLAB today. Making FIR filters is easy. Making linear phase FIR filters is a bit trickier but still easy. Making minimum phase FIR filters took me a long time to figure out, but now I have a methodology that works. I made a 4096...

Frank B. Thanks for checking on that. I'm going to experiment some more with my setup to see if I just have a lazy chip or I'm doing something wrong. I still need to replace the caps in my receiver to get my bandwidth opened up - that might be part of my issue.

Hi Frank, I see what you mean about the AD8333. That is not as great as it first appeared. I have spent a great deal of time trying to find a quadrature detector chip that is a little faster than the one we are using. The Potato Chips fit the bill, but I tried to get some and they are not...

This almost looks like it is designed to work with the Si5351. https://www.analog.com/media/en/technical-documentation/data-sheets/AD8333.pdf Could have different transformers for LF and HF to have a pretty high performance SDR from 40 kHz to 50 MHz.

Hi Frank. Thanks for the explanation! I don't know why there should be a linear calibration factor. If the reference frequency is corrected, everything "should" fall into place. But some of these chips play weird tricks so who knows? I put my PCM1808a board on the other side of a shield so...

Hey Les Happy to accidentally help. :-) I was playing with the different bandwidths and noticed that the 256k didn’t work but the 192k works fine. Trying to figure that out. The chip is only rated for a sample rate of 96 kHz so maybe this setting is the clock frequency for the PCM1808? I’m...

I am working my way through the code and figuring it out bit by bit. There is a lot of stuff in there! One thing that I am confused about is that the sampling rate can be set up to 256kHz. But the PCM1808 spec sheet is only rated to 96kHz. Are you pushing the chip beyond its specified limit or...

Thanks Frank B. It is within a few Hz at 1 MHz and 30 MHz both. I'm happy with that. I've thought about hooking up one of my little GPS boards to give it a precise 1 Hz clock. Then I can run a fixed clock out of the Si5351 into a Teensy pin and set it up as a counter. Then measure the error once...

Never mind Frank. I figured it out. I was tuning into one of the harmonics near my signal generator. After reading through the text doc in the Si5351 library... the calibration is in parts per billion. So I measured the frequency error and divided it by the frequency and multiplied it by one...

Hi Frank, Thanks! I'm excited to start experimenting. I have the latest code and the correct Si5351 library. I think you have the calibration_constant and calibration_factor reversed. The calibration constant is 0 and the calibration factor is 1e9. I tried your calibration method but I think...

My newly build receiver is off in frequency. I have the calibration constant set to 0. My crystal is 27 MHz and I'm using the DD4WH hardware setup. I set a test oscillator up at 1 MHz and my receiver receives it at 0.978373 MHz which is 21627 Hz low. This is also 21627 ppm so not just crystal...

Here are some pictures of my finished Convolution SDR. Now I need to put some filters in there.

That makes sense. So long as there is a divide by 2 in the output register of the Si5351, the 2xfo should work fine. I also saw somewhere that two outputs of the Si5351 can be set to the same frequency but with a 90 degree phase offset. I think Hans Summers (QRP Labs) figured it out, but I don't...

@DD4WH The reason for using the 4xfo is this: Crystal oscillators begin with a sine wave. A crystal is a very narrow filter - in frequency terms, an FFT with one bin turned on and the rest off -- so only one frequency (so a sine wave). Converting a sine wave into a perfect square wave is nearly...

Have you made any progress on the variable gain op-amp idea Frank? I have been thinking about it. As you say, keeping the level into the ADC high but not overloading is important for the dynamic range of the receiver. Also, I have been using a magnetic loop antenna which typically has better...

Those are impressive measurements Tisho. If you want to double check that you are getting good numbers, you can add more attenuation and see if the NF changes (it should not). But with more attenuation you also have to be careful that your signal is not leaking from the signal generator to the...

Hi Tisho, Your plan to measure noise figure sounds excellent. It is a great way to quantify your improvements as you refine your receiver. The tricky part of NF measurements is the bandwidth. Noise figure is the commonly used performance metric for UHF and microwave receivers because they have a...

I bought my terminators from this place: https://www.w5swl.com And this is the model: https://www.w5swl.com/Mini-Circuits-SMA-Male-14-Watt-Termination-Load-DC-2GHz_p_6170.html Measured with my old Fluke 79 III meter, which I admit has not been calibrated in years, I measure 49.9 Ohms on both of...

I need to fix my example above. I forgot to include the gain of the audio amps. But the principle is still correct.

Hi Tisho, I always choose TI parts if I have the option. My only reason for this is that their data sheets are very good and almost always have the necessary info for a designer. If they don't tell you how they tested something, it isn't really much use, but TI does tell you most of the time. I...

QEX requires a subscription. But all the software and PCB files etc. are available here: http://www.arrl.org/qexfiles Look for the January/February article by James Koehler. I am almost positive that the ARRL made the article available publicly, but I can't find the link. This is the magazine -...

WH7U - only be careful when buying these switches with Aliexpress - defective non-functional pieces have been reported at some retailers. I can confirm that. Thanks for the warning radek. I usually buy chips at Mouser here in the US. I've had bad luck with chip clones over the years.

Here is a picture of my nanoVNA. This is the authentic version. The two 50 Ohm terminators that are not in the box I purchased separately (the ones that come with the nanoVNA are not very accurate). I recommend getting a couple of 50 Ohm terminators that are 1% or 2% if you want to do accurate...

If you decide to get a nanoVNA, make sure you don’t get one of the cheap clones. Go to nanovna dot com and get that one. I don’t know why people are making cheap clones of something already so cheap but it is a big problem according to the nanovna forums. I will post a picture of mine which is...

I have a nanoVNA. It works well for an inexpensive VNA and you can’t beat the price. But I also built a VNA from an article in the Jan 2020 issue of QEX that I prefer. Either one will work well for testing the switch. And they really help with filters and antennas.

Thanks Tisho. Those are nice little switches if they work well at low frequencies. The manufacturer designed them for GSM and WCDMA so they likely work fine but maybe they didn't bother to test them outside the intended range. I am a little worried about the footnote in the PE4259 data sheet...

Hi Tisho, Nice work in the receiver. I have a question. The data sheet for the PE4259 says that the bandwidth is 10 MHz - 3.0 GHz and the PE42641 states 100 MHz - 3.0 GHz. Have you tried these switches at lower frequencies? I know data sheets don't always tell the whole story. Bill

I'm in a meeting at work while I'm typing this, so I hope it makes sense. It might clear up some things in the discussions I have been catching up on. As far as the noise discussions for different amplifiers etc., here is how I think of it (for what its worth). A high performance receiver is...

Here is the schematic. I had trouble attaching it.

Hi Frank, You could do that? Interesting idea. Normally, at low voltage, FET switches are better at pulling signals to ground. They may struggle if floating if the audio gets near Vdd. I have used the technique in the attached schematic (from the book Experimental Methods in RF Design).