I tried at the time, and it was still that bad to disconnect the RX of the LO, so I changed a version, today I have received the PCB, tomorrow I will solder in my free time, compare the results before and after, which is also a good knowledge, before I thought that was enough shielding

On Mon, Jun 5, 2023 at 08:42 AM, m0wid wrote:

Interesting - you have used a larger higher resolution display - nice!

I do not see these 30MHz harmonics on the high range, though I do have a spurious signal at 270MHz, so I think there is more to it than just filtering.

For the low range sweep the RX SI4432 is the detector, while in high range the LO SI4432 is the detector.? If I turn the ref output on (this is generated by the LO SI4432) I get similar spurious response to your screen shot (actually much worse), even with no connection from the ref output to the input.? I wonder if there is a software bug and the ref output is not being turned off properly?? Can you test the high range with the ref output on and off?

If the spurious responses are still there with the ref output off then I think you need to look at the layout around the LO SI4432 and see if there is a clock trace nearby or underneath.

You could also possibly try removing the capacitor between the RF switch and the SI4432 and see if the spurious response remains.? Then you will know if the signal is from within the SI4432 or outside.

Interesting - you have used a larger higher resolution display - nice!

I do not see these 30MHz harmonics on the high range, though I do have a spurious signal at 270MHz, so I think there is more to it than just filtering.

For the low range sweep the RX SI4432 is the detector, while in high range the LO SI4432 is the detector.? If I turn the ref output on (this is generated by the LO SI4432) I get similar spurious response to your screen shot (actually much worse), even with no connection from the ref output to the input.? I wonder if there is a software bug and the ref output is not being turned off properly?? Can you test the high range with the ref output on and off?

If the spurious responses are still there with the ref output off then I think you need to look at the layout around the LO SI4432 and see if there is a clock trace nearby or underneath.

You could also possibly try removing the capacitor between the RF switch and the SI4432 and see if the spurious response remains.? Then you will know if the signal is from within the SI4432 or outside.

Dave

you are right, some series resistor could reduce the harmonics from the clock,but I debug through series resistors, and the best is -80dbm(before it was -70dbm, see the picture)



And I chose SAHi and SALo two modes to set the same 240-350MHz, the test results are different.



So I attribute the reason to SAHi mode because it doesn't go through the filter.

and I mistakenly wrote it to change to 130MHz, then the accuracy should be that the IF can choose a 240MHz SAW filter.

Can't the IF filter be replaced?

@ blackberryer

I cannot see the image unfortunately.? 30MHz is likely to come from the oscillator traces.? Any oscillator tracks routed near the modules or RF signal lines?? Maybe some decoupling caps or series resistor could reduce the harmonics from the clock.? Another possibility could be to add a simple High Pass filter to the high range input.

I am struggling a little to understand what you have written.? I think you are suggesting a method to see 800Mhz signals using the mixer and IF filters.

The IF SAW filter frequencies are fixed and quite narrow, so the signal into the detecting SI4432 needs to be in the range of the IF filter passband, around 433.9MHz.? Of course different SAW filters could be used with different passband frequency.? SAW filters are bandpass filters.

A 130MHz SAW filter is of no use as the SI4432 only receives in the range 240-930MHz.

If the LPF is bypassed then you could mix a LO of (800-433.9 = 366.1MHz) with the 800MHz, however then a signal at 433.9-366.1 = 67.8MHz would be detected and possibly give odd results.? This might be OK so long as the user understood that this could happen.

You could possibly switch in a high pass filter (or bandpass filter) when looking at frequencies above the IF frequency, but there would be a range of frequencies around the IF frequency that would not be usable (say 350-500MHz).? The low pass filter or high pass filters could be external to keep things simple.

For most amateur radio applications having reasonable results in the 1-350MHz region is more useful than 500-800MHz, also the gap between ranges is not helpful, hence the design is optimised for the lower frequencies.


Good luck

Dave

Is this understanding correct?

Then the image below is a screenshot after I switched to HF mode before, and the input was completely unconnected.
As you can see, it seems to be a lot of harmonics generated by 30MHz

In low mode the input signal is mixed with the Local Oscillator from the SI4432 to produce the IF.? This IF is filtered in the SAW filters (B3550 or whatever you used in your build) - the IF frequency is therefore limited to be in the passband of these filters.? The SI4432 does some more DSP filtering internally.

The #define statements shown in your pictures are not for the low mode sweep but for the test modes for the SI4432 FIR filters and the SAW filters.

The low input is filtered by the 350Mhz low pass filters.? These are there to avoid alias products, and also to make the output in signal generator mode fairly clean.

In the high mode the signal goes directly into the SI4432 with no external filtering.??

Remind me of the issues you have with unclean traces - in high mode, low mode or both???

Dave M0WID

Hi,m0wid


2.
And I see that my_SA.h limits the IF/RX frequency，Why is the IF frequency limited to a maximum of 500MHz?
In principle, isn't it okay to choose an IF frequency that is larger than the sweep frequency?

Hello,

Where to find version SimpleSA ESP32 0.14? to do some tests
or put the zip file
I have the 0.15, 0.11, but i want test the 0.14
Thank's

骋é谤补谤诲,
Please give me your postal address in a private message and I will send you a Si4432 module. If you need a row of 1.27 mm spikes, I can send one.
--
Gyula HA3HZ

Hello all, Hello Dave,

hello,
here the answer about the 5 transistors
Interisting....

cdt

开云体育

开云体育

hello,

John,

It looks? like you need to expose some copper on your input to solder to.

-John K6JDS

No error, your pcb is correct.

Nice job, let us know how well it works.

Bill - the capacitor is made up of the pads on the top and bottom side of the pcb
--
Terry VK5TM
https://www.vk5tm.com

William

here the original project
I think no error??
You confirm or ?

cdt