NanoVNA-H
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hugen79
Noise improvements.
I improved the noise adding few caps to the Silicon Labs clock generator chip and now the standalone instrument is fully working up to 1.5GHz with only a very little residual noise above 1.4GHz that it is appreciable in the Smith chart only. I still have some issue with the PC communication because of the battery charger that disturbs the clock. I already thought a solution for this too, but I'm waiting for the sot23 P-MOSfet, to check if it works as thought. Once I fixed it I'll publish the "how to" of the whole hardware fixing. In the meantime I have a couple of desiderata to your code.
- the flashing LED 2 is very noisy and useless. It's much better to keep it off, if your intention was to give a pace indicator, I suggest you to implement it as a virtual indicator somewhere on the LCD screen (I currently removed its limiting resistor to keep it off).
- Since there is still a little noise above 1.4GHz, It would be great if the calibration was done not by one acquisition of the raw data per calibration step as it is now. It should be better if you get more scans of the raw data and average them to get the correction coefficients averaged on more scans (say 10 scans, for example). This will take a little more time during the single calibration steps, but it should warrant that the noise is corrected on its averaged value and not randomly on the instantaneous values acquired during the single scan. Have a great day. Massimo
regarding to LED 2, NanoVNA-Q disable it during sweep cycle to avoid noise: https://github.com/qrp73/NanoVNA-Q/releases
so, there is no need to desolder something. You can just change firmware.
Not really so. The clock generator's inner PLLs are always locked also during the non scanning time. So the perturbation on the integrators of those PLLs still deteriorate their output phase noise during the scan time.
BTW, even if I seen that in the latest versions the LED 2 is apparently off during the scan, using a DSO on the limiting resistor pad, I always see some voltage spikes of few ms in duration there.
For these reasons I removed that resistor and the noise above 900MHz dropped a lot, despite I already downloaded the latest version of NanoVNA-Q.
My current mods consist on:
- added one 4.7F X7R capacitor in parallel to C9 and one other on C10
- added one 68uF/6.3 tantalum capacitor in parallel to C9 and the 4.7uF already in parallel as above
- added one 68uF/6.3 tantalum capacitor soldered on U3 input pin and grounded to the ground plane near Y1
- removed R3
Doing the above, after a correct calibration, I get a Smith chart plot with just a little noisy plot of 2/3mm above 1.3GHz, making the instrument well usable in the HAM radio 23 cm band for antennas and filters checkings. The SWR plot at 1.5GHz with the calibrated dummy load on the CH0 port shows 1:1.1 max 1:1.2 spikes, but below 1.3GHz is flat to 1:1 The return loss with the reference load used for the calibration, at 1.5GHz is better than -25dB on any board I checked, not that bad indeed I did the test on 6 boards of three different versions, two having the ground clips and one having the nanoVNA-H board. And the results are almost the same. Attaching the USB port, I still have noise above 900MHz, but I already checked that it is due to the battery charging. Detaching the battery positive wire and powering the VNA by the USB only, after a new calibration, the results are the same for the stand-alone running reported above. For this reason I planned to put a P-MOSfet in series to the battery to detach the battery from the circuitry when the instrument is turned on and the power come from the USB port. This way the battery charging will be still allowed when the instrument is turned off, but it's thought to remove that noise during the instrument is powered on. I just to check it when the MOSfets will be delivered.
Have a great day.
Massimo
Not really so. The clock generator's inner PLLs are always locked also during the non scanning time. So the perturbation on the integrators of those PLLs still deteriorate their output phase noise during the scan time.
No, it performs PLL reset at the beginning of sweep. So, any voltage fluctuations outside sweep time doesn't matter.
NanoVNA-Q has 10 ms stabilization delay after LED off, before it starts sweep.
And NanoVNA-Q don't blink with LED at all until end of sweep.
At this point I don't really know why I seen that sensible improvement after having removed R3.
Anyways, I'm sure that I also seen some glitches during the sweep. Let me return to home because now I'm in office and I can't check it one more time until I'll be back to home.
You're seen it, because used firmware which uses LED blinking during sweep. NanoVNA-Q firmware disables LED during sweep and don't blink until the end of sweep.
No, I'm not sure that I seen it with V0.4.3 indeed, but I'm sure that I seen it with your V 0.4.2, and (if I'm not wrong) that function should have been already done.
One doubt: what is your noise above 1.3GHz without any additional caps on the 5V & 3.3V power lines? My doubt is that having increased the capacitance on the 3.3V U3 output, that could have introduced some sort of instability at the voltage regulator output after current pulses on it's input that lasts more than those 10ms. I must check resoldering R3. I'll tell you this night.
Hi qrp73. yes you are right and I was wrong I didn't realized that when the LED2 is on, there is a PWM signal on it and having the horizontal scale of the DSO on 1ms/div I probably confused the ON state with OFF state of the LED2 when the PWM was there. Here below you can see the 1.3GHz and 1.5GHz with the LED blinking. (please note that I had to detach the battery + wire to get these plots from the nanoVNA Saver, because I still haven't received the MOSfets). What do you think about the 10 time averaging suggestion during calibration? It could better correct the scan above those 1.3GHz.
Thank you for sharing your work about this nice device.
Noise problems introduced by USB connection I will use the new power chip in NanoVNA-H V3.4 to improve this problem. I will try to increase the capacitance of the si5351 to reduce noise. The problem of LED flicker noise can be improved by software. If you prefer, you can send your address to my email at [email protected] and I will send you the modified PCB. Thank you!
hi hugen79, first off all, thank you for considering this issue, and for sharing your work on the nanoVNA-H board.
Since I had 6 nanoVNA on the table (only one was mine, the others were owned by friends of my local radio-club, I'm not a collector :-) of course), I believe I missed to update one and probably I did the check on that one, because I well remember how the noise dropped down after having removed R3. Anyways, considering how much the instrument is sensitive to the power supply noise I would keep that LED off since in my opinion is useless, but this is just an opinion of course. About the USB connection I already ordered the MOSFETs and I hope they'll come here soon (Italian Postal Service permitting). I planned to detach the battery when the USB power is applied and the instrument is turned on, it should take just 3 components comprising the MOSFET, not that complicated indeed. I probably mount the components on a very small piece of prototyping board and solder it in place of the battery connector.
Anyways your nanoVNA-H 3.4 PCB is surely well accepted, I 'm curious to know how it is handled the new power chip.
By the way, do you know from where it cames the R40, C45 and C46 network configuration? I admit that I know very little about the electrical layer USB specs, but do you know what's the usefulness of the 2ohm resistor in series to the second 10uF capacitance?
I'll send you a direct e-mail for the 3.4 PCB.
Have a great day.
Massimo
The specifications of r40, c45, and c46 are from the data sheet of Ip5303. The series r40 and c45 are used to ensure the loop stability of ip5303. However, when an external USB power supply is connected, the MOSFET inside the ip5303 turns on and uses an external USB power supply, causing external interference to enter the power supply. For the new PCB, I will use the FM9688, a power chip widely used in Bluetooth headset chargers in China. The chip charging circuit and DC-DC circuit work independently, and the external circuit is simple and easy to install on the nanoVNA PCB. on.
Hi hugen79, thank you for the explanation, I seen that in the datasheet it was there, but (at least in the English version) I didn't find any explanation for it.
However, when an external USB power supply is connected, the MOSFET inside the ip5303 turns on and uses an external USB power supply, causing external interference to enter the power supply.
I'm not sure the noise come from the USB line, I suppose is something due to the pulsed current into the battery during the charging process, because if you remove the battery and leave the USB power alone the noise is no longer there. For this reason I thought to put a MOSFET based switch between the battery and the Ip5303. About the FM9688: I haven't found the english datasheet. I'm no way able to read the Chinese ideograms :-( Have a great day. Massimo
causing external interference to enter the power supply.
According to my tests, this is not external interference. You can apply very clean external power (with no noise), but anyway it will be noisy. Also it is not related with cable, because there is no noise when usb cable is connected, but external voltage is not supplied.
I think the root of cause may be the following:
- IP5303 generate noise
- external voltage leads to a little different power supply voltage and it leads to some change in behavior
causing external interference to enter the power supply.
According to my tests, this is not external interference. You can apply very clean external power (with no noise), but anyway it will be noisy. Also it is not related with cable, because there is no noise when usb cable is connected, but external voltage is not supplied.
I think the root of cause may be the following:
- IP5303 generate noise
- external voltage leads to a little different power supply voltage and it leads to some change in behavior
The difference in voltage will cause the gain of the sa612 to differ, resulting in errors. Maybe a separate charge pump can further reduce the noise, and I will do some tests.
I perfectly agree with qrp73 when he wrote:
According to my tests, this is not external interference. You can apply very clean external power (with no noise), but anyway it will be noisy. Also it is not related with cable, because there is no noise when usb cable is connected, but external voltage is not supplied.
In my opinion the problem is in the charging current pulses coming from the USB supply that produces inevitable little voltage spikes on the battery, since the voltage of the battery influences the calibration, in my opinion it's clear that those spikes are the cause of the performance deterioration.
I don't know if FM9688 will fix the issue, for doing that it should have two different switching mode PSU inside: one step-up for driving the load and one step-down for charging the battery; they should have very different PWM frequency to allow the step-up to be more reactive to the battery voltage changing caused by the lower frequency step-down charger. In the datasheet, I see the schematic of the FM9688 and I don't see other than one inductor in that design, this lead me to think that it should not be much better than the Ip5303 under this context, but I could be wrong, of course.
Have a great day.
Massimo
I tried to replace the XC6206 with an ultra-low noise LDO RT9193, and I found that the noise has dropped. I will make a PCB test. hugen
I tried to replace the XC6206 with an ultra-low noise LDO RT9193, and I found that the noise has dropped. I will make a PCB test.
Nice one. If it's confirmed the "thorn in the side" of the instrument is the clock generator, since the mixers are not powered from the 3.3V regulator.
I tried to replace the XC6206 with an ultra-low noise LDO RT9193, and I found that the noise has dropped. I will make a PCB test.
Nice one. If it's confirmed the "thorn in the side" of the instrument is the clock generator, since the mixers are not powered from the 3.3V regulator.
Sorry, I made a mistake. Due to my wrong connection to the RT9193 pin, the actual output voltage of the LDO rises to 3.6V, and the performance improvement is due to the voltage rise. But this gave me a new idea to improve performance, I am making new attempts.
https://github.com/qrp73/NanoVNA-Q/issues/13#issuecomment-552679259 Mine(Green PCB) was around 6.5 MHz
qrp73/NanoVNA-Q#13 (comment) Mine(Green PCB) was around 6.5 MHz
Thanks for your feedback, I will modify the schematic in v3.4.
Hi hugen79,
Sorry, I made a mistake. Due to my wrong connection to the RT9193 pin, the actual output voltage of the LDO rises to 3.6V, and the performance improvement is due to the voltage rise. But this gave me a new idea to improve performance, I am making new attempts.
Don't worry: anyone who has never made a mistake has never tried anything new! (Albert Einstein)
:-)
I would have here the mosfets and tell you if the patch works for the USB powering. Anyways, as I have them here, I'll surely inform you about how the patch works.
For the 7.5/6.5Mhz peak issue: I didn't noticed of it, but I must say that I have already added the 100nF on the mixer as per the NXP datasheet. Since I don't see anything there on any of the 3 different versions I have here, I can confirm you that it works fine. I didn't reported that caps mod, just because I was convinced that they did nothing to the instrument, since I never looked to that narrow range before. My compliment to Owen for having catched that issue. Here in Italy we say: "he catched the the needle in the haystack".
Hi coralenka Fantastic plots, how do you get them so noise-free up to 1.5GHz?
In the meantime, I just received the MOSFETs and checked the USB switcher and it works good, but above 1.3GHz as per the battery powered mode the noise is still there.
The mod consists of place on a small piece of proto-board (3 by 2 pads) an AO3401 P-channel MOSFET as follows: DRAIN connected to the positive wire of the battery SOURCE connected to the PCB positive battery pad GATE connected to the ANODE of one 1N4148W diode and a 10kohm resistor (both on the little piece of proto-board). The diode CATHODE is connected through a short wire to U3pin3, while the other pad of the 10kohm resistor is connected through a short wire to U2pin1. Doing that circuitry, the battery charges only when the nanoVNA is not powered but the USB plug is connected to a current source. When the nanoVNA is powered on, the battery is disconnected and the noise is as in the plots attached below. Have a great day.
Massimo
HiI made no mod to my device yet
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Pe joi, nov. 14, 2019 la 0:45, Pmax65[email protected] a scris:
Hi coralenka
Fantastic plots, how do you get them so noise-free up to 1.5GHz?
In the meantime, I just received the MOSFETs and checked the USB switcher and it works good, but above 1.3GHz as per the battery powered mode the noise is still there.
The mod consists of place on a small piece of proto-board (3 by 2 pads) an AO3401 P-channel MOSFET as follows: DRAIN connected to the positive wire of the battery SOURCE connected to the PCB positive battery pad GATE connected to the ANODE of one 1N4148W diode and a 10kohm resistor (both on the little piece of proto-board). The diode CATHODE is connected through a short wire to U3pin3, while the other pad of the 10kohm resistor is connected through a short wire to U2pin1. Doing that circuitry, the battery charges only when the nanoVNA is not powered but the USB plug is connected to a current source. When the nanoVNA is powered on, the battery is disconnected and the noise is as in the plots attached below. Have a great day.
Massimo
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I made no mod to my device yet
Hi coralenka, interesting. Has your nanoVNA the battery installed? I ask because when attached to the USB port, I experienced a great increase in noise bove 900MHz in all the 3 hardware versions I checked. Your seems incredibly quiet even when attached to the PC. Have a great day. Massimo
Yes the battery is attached and at the same time the device is connected to the computer...I use the hardware version 0.4.0-273 de YO4AUL
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Pe joi, nov. 14, 2019 la 15:14, Pmax65[email protected] a scris:
I made no mod to my device yet
Hi coralenka, interesting. Has your nanoVNA the battery installed? I ask because when attached to the USB port, I experienced a great increase in noise bove 900MHz in all the 3 hardware versions I checked. Your seems incredibly quiet even when attached to the PC. Have a great day. Massimo
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Hi coralenka,, it's gorgeous. Could you publish a photo of the nanoVNA? Have a great day. Massimo
This is my device
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Pe joi, nov. 14, 2019 la 20:12, Pmax65[email protected] a scris:
Hi coralenka,,
it's gorgeous.
Could you publish a photo of the nanoVNA?
Have a great day.
Massimo
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HI coralenka, I'm not sure, did you send anything about how it looks your nanoVNA? I can't see anything.
This is my device
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Pe vin., nov. 15, 2019 la 1:02, Pmax65[email protected] a scris:
HI coralenka,
I'm not sure, did you send anything about how it looks your nanoVNA?
I can't see anything.
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It seems there is something wrong in the file handling because I can't see anything. Could you send the photo to my e-mail? My address is [email protected] I would like to know what HW it is, because I've some nanoVNAs from friends of my local radio club to modify and above 1.3GHz it seems really hard task to comply. Thank you for considering my requests. Have a nice day. Massimo - IK1IZA