Re: Quick and dirty GPSDO build by F2DC and me.
Very good !
I use an STM32F CPU with it's main input clock driven from a 10MHz?OCXO 143-141 (plenty of cheap used ones on aliexpress), I feed the filtered long wave RF signal (from a small tuned ferrite antenna) from either the french 162kHz caesium referenced transmitter or the UK BBC 198kHz rubidium referenced transmitter into one of the ADC ports. I then do software PLL I/Q (in firmware) and use the CPU's DAC output to correct the 10MHz OCXO-143 oscillator. It's as stable as the either of the two transmitters (which are regularly checked/calibrated once a week I believe).
The 10MHz OCXO output I also feed into an Si5351 chip (Si5351's also work with 10MHz clock input if you want) to generate any other frequency I want up to 160MHz (SDR reference input's, frequency counters etc).
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Re: Quick and dirty GPSDO build by F2DC and me.
Very good !
I use an STM32F CPU with it's main input clock driven from a 10MHz?OCXO 143-141 (plenty of cheap used ones on aliexpress), I feed the filtered long wave RF signal (from a small tuned ferrite antenna) from either the french 162kHz caesium referenced transmitter or the UK BBC 198kHz rubidium referenced transmitter into one of the ADC ports. I then do software PLL I/Q (in firmware) and use the CPU's DAC output to correct the 10MHz OCXO-143 oscillator. It's as stable as the either of the two transmitters (which are regularly checked/calibrated once a week I believe).
The 10MHz OCXO output I also feed into an Si5351 chip (Si5351's also work with 10MHz clock input if you want) to generate any other frequency I want up to 160MHz (SDR reference input's, frequency counters etc).
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Re: Quick and dirty GPSDO build by F2DC and me.
Interesting
- I have a pile of old Motorola Oncore M12 GPS modules.
They are all EOL due to the data roll-over issues but does anyone know if I can still use them for the 1PPS output?
Thanks, Larry
On Tuesday, May 11, 2021, 11:05:56 a.m. EDT, Erik Kaashoek <erik@...> wrote:
Anyone looking for a GPSDO with a frequency accuracy in the order of 1e-8 should have a look at this:? I made a quick and very dirty build of his design using only 4 modules found on eBay - Arduino nano - GPS module with 1PPS output (neo-6M or better, I used neo-7M) - SI5351 module with 3 outputs - 16x2 LCD display and some wires etc,?running from a bench 5V supply.  The Arduino SW was modified (??) to have a adaptive measurement time depending on the frequency error observed. With a stable temperature of the SI5351 crystal and the largest measurement/correction cycle time of 400 seconds the stability was better than 0.01 Hz, or 0.003 PPM? The schematic as published by F2DC  My current SW on github does not need the serial data from the GPS, only the pulse per second. The CLK1 output of the SI5351 is freely configurable to any valid SI5351 output frequency such as 10MHz or 100MHz.? Have fun -- HBTE Files section:? /g/HBTE/filesErik, PD0EK
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Re: Convolution - a possible way to provide improved RBW for the tinySA?
It's actually deconvolution ( ?) and it can work as the tinySA RBW filters are well defined and are fairly steep. The required memory may be too high and the frequency resolution is only 260Hz allowing maximum 10 substeps. The required scan time with 10 substeps is at least a factor 10 higher. I may look into this but do not have too much hope. -- HBTE Files section:? /g/HBTE/filesErik, PD0EK
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Re: Quick and dirty GPSDO build by F2DC and me.
Here you see the adaptive algorithm working. It starts with 1 second per measurement and as long as the error is below the measurement accuracy for the current measurement time the measurement time is doubled. If the frequency change is above 10Hz? per 100MHz per measurement interval the measurement interval is halved. Here you see the interval automatically being reduce due to temperature jump and after correction automatically being increasing again.  -- HBTE Files section:? /g/HBTE/filesErik, PD0EK
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Convolution - a possible way to provide improved RBW for the tinySA?
I have very little knowledge of DSP, so would appreciate if anyone here can help out.
One of our club members M0KGW suggested that the RBW of the tinySA or homebrew simpleSA could be improved using convolution.
The idea is if you know the response of the SI4432 FIR filters, (we can measure this) then by sampling at smaller frequency step increments and using convolution then it should be possible to recover some of the information to get improved resolution bandwidth (RBW).? Improved RBW is desirable for measuring intermodulation of transmitters.
Consider say two signals at close spacing, say 1kHz apart.? The SI4432 has a minimum RBW of 2.6kHz so by stepping at say 2kHz intervals it is not possible to pull out these two signals.? If a smaller frequency step is used, then as the signals come in and out of the filter passband the RSSI value will change - the RSSI at each frequency step will be the sum of the filter response for each signal.? Given the frequency response of the filters it should be possible to extract the two signals using convolution in the frequency domain.
45 years ago I might have been able to work out the maths for this, sadly no longer.? Also sad to say I had not even heard of convolution before M0KGW mentioned it.
Is this idea practical and if so how to go about coding it?? I would certainly like to give it a go and see how it works in practice.
73
Dave M0WID
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Re: Quick and dirty GPSDO build by F2DC and me.
Nice!?
Yet again you tempt me into building something - I already have a GPS with 1sec pulse and serial connected to a nano currently just used as a shack clock and a 1pps repeater (hardware, not via the Nano) for a QRP-labs Ultimate 3.
Any feel yet as to how quickly the output compensates for temperature changes?
Dave M0WID
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Quick and dirty GPSDO build by F2DC and me.
Anyone looking for a GPSDO with a frequency accuracy in the order of 1e-8 should have a look at this:? I made a quick and very dirty build of his design using only 4 modules found on eBay - Arduino nano - GPS module with 1PPS output (neo-6M or better, I used neo-7M) - SI5351 module with 3 outputs - 16x2 LCD display and some wires etc,?running from a bench 5V supply.  The Arduino SW was modified (??) to have a adaptive measurement time depending on the frequency error observed. With a stable temperature of the SI5351 crystal and the largest measurement/correction cycle time of 400 seconds the stability was better than 0.01 Hz, or 0.003 PPM? The schematic as published by F2DC  My current SW on github does not need the serial data from the GPS, only the pulse per second. The CLK1 output of the SI5351 is freely configurable to any valid SI5351 output frequency such as 10MHz or 100MHz.? Have fun -- HBTE Files section:? /g/HBTE/filesErik, PD0EK
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Re: How mixer responses to different PORT and LEVEL
Not wanting to answer your questions in detail I suggest you to study the concept of Intermodulation Intercept, both for 2nd and 3rd order. This concept states that with every dB reduction of one of the signals below the intercept point the 2nd order intermodulation will reduce with 2dB and the 3rd order intermodulation with 3dB. Once you know the 2nd and 3rd order intercept points of a mixer (mostly specified for 3rd order as IIP3 level, +15dBm for the ADE-1 mixer when driving the LO port with +7dBm) you can calculate the impact of other signals at the RF port. Signals leaking from one port to another are simply reduced by the isolation between the ports and from there seen as if they are originating from that port. -- HBTE Files section:? /g/HBTE/filesErik, PD0EK
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How mixer responses to different PORT and LEVEL
Sorry long post
Since i saw posting on mixer at time of TinySa development hot time in this forum, i would appreciate advises on how mixer reacts to signal coming from different PORT and LEVEL.
This is for ham receiver. Normal ham receiver has filter to reduce the f3 and f4 as described below. Assume it only has average filter and it is in strong interference field day, so, f3 and f4 still very strong after leaking through the less than perfect filter and reach the mixer. Assume mini circuit ade-1 mixer as used inside TinySa
Actual freq, wanted receive freq is 7.03MHz. Two unwanted freq is 3.52 and 3.51 MHz and their sum is same 7.03 MHz. Modern ham receiver have half octave filter and will attenuate it quite a bit but can still leak through in field day or similar. Yes, they do make contest grade receiver with extra strong filter but that is not the issue here. My question is how this mixer will response in what manner.
Question 1.
Does mixer act differently toward "a pair of signal both coming from RF port (as in ham receiver unwanted out of band interference) and the normal pair of signal, wanted signal, called f1, from rf port at says -90 dBm and a much stronger signal from Lo port at 7 dBm, called f2.
As the example mixer, the IF port will have sum and difference at -95 dBm, as 5 dB conversion loss at f1+f2 and f1-f2.
As for the unwanted interference coming from RF port, called f3 and f4 , is it true that it need to be "quite strong" before f3 and f4 can produce their own set of mixed output at IF port, at f3+f4 and f3-f4 (which is no use here)
Beated product IMD interference signal, f3+f4 shall has same IF frequency as wanted signal f1-f2 (or f2-f1)
Question2
When both f3 and f4 are weak and at similar level as the wanted f1, -90 dBm. How much dBm will the mixed output of f3+f4?? Will it be very weak?
Question 3
What will happen when f3 and f4 both rise to says, -40 dBm, quite strong as incoming signal but much less than the normal beating signal Lo at 7 dBm? Will it start to produce siginificant output at f3+f4?
Question 4.
What are the signal level condition that
f3 and f4 can generate at IF port, f3+f4, at same -95 dBm of the wanted f1-f2 signal?
How strong f3 and f4 need to be? Assume f3 and f4 are same level
Sorry for long post. Many thanks for your time in reading this. Much Appreciated.
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Re: third order intermodulation measurement
On Sun, Mar 14, 2021 at 05:48 AM, dsf sdf wrote:
Hi,
did someone try to measure IMD with 1 to 2 kHz carriers spacing with TinySA?
What is the frequency limit?
? ?The following link may be of assistance,???, the information is for the commercial implementation of the tinySA using one of its automatic measurement features.? My opinion is that, since the minimum RBW of the tinySA is 3kHz, resolving carriers with 1 to 2kHz spacing for IMD measurements may not be possible. Herb
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third order intermodulation measurement
Hi,
did someone try to measure IMD with 1 to 2 kHz carriers spacing with TinySA?
What is the frequency limit?
73' F4BSP
#imd
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Interesting and easy to understand instruction video for NanoVNA:
?
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Might be interesting...
Arv _._
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Might be interesting...
Arv _._
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Re: Noise floor at low frequencies for TinySA with Arduino Zero
Hi Dave,
thanks for the hints with the vias to the lower ground plate. I used the same "flying" construction for the BPF as Erik did - and after adding a lot of vias this reduced the noice floor at low frequencies.
The measurement of the BPF shows now also a lower bandwidth. ?~ 0.7MHz @? -3dB measured from max. peak @ 433.9MHz.
Also the noise floor between 0 - 2 Mhz is now lower and is similar to yours - but still not that good :-)
The measurement shows? S12 (should be the same as S21) and the voltage. Unfortunately I was not 100% familiar with this network analyzer and could not switch to the dBm scale.
Next step will be to use the recomended footprint from the datasheet of the SAW filter.
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Re: Can you use multiple outputs of SI5351 in a high performance VNA?
On Wed, Dec 2, 2020 at 12:17 PM, NahuelArg wrote:
Hi Erik. I'm trying to make an antenna analyzer based on the si5351 but i can't accomplished.
Can I suggest you take a look at the nanoVNA source code? In the nanoVNA the two outputs of the SI5351 are constant 5kHz apart. ? -- HBTE Files section:? /g/HBTE/filesErik, PD0EK
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Re: Can you use multiple outputs of SI5351 in a high performance VNA?
Hello
"high performance" - please define "high" . There is always cross talk in any circuit. It is only a matter of how much. Using two devices should not break the bank I guess.
antenna analyzer
- you have to run CLK0 on PLLA and CLK1 on PLLB
- have you initialized correctly?
- are you loading FMD0 + OMD0 and FMD1 + OMD1 "in pair" correctly? Per
Bo
www.rudius.net/oz2m :: www.rfzero.net
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Re: File /WA2FZW - M0WID ESP32 - ILI9341 Version of the TinySA/simpleSA_0_11.zip uploaded
#file-notice
Hi Dave,
thanks for the help. I tested version 0.12 today, the color setting for the markers works really well after the TFT_eSPI v2.3.4 upgrade.
At first it didn¡¯t work - but I found the cause and now everything is fine.
The reason was that the folder was damaged somewhere during the upgrade and only repaired after the libraries / TFT_eSPI folder was completely deleted and reinstalled.
 -- Gyula HA3HZ
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Re: File /WA2FZW - M0WID ESP32 - ILI9341 Version of the TinySA/simpleSA_0_11.zip uploaded
#file-notice
Hi Gyula
I am using the latest version of TFT_eSPI available from the arduino library manager - 2.3.4.? Any version later than 2.2.16 should be fine.? I see 2.2.16 is not available in library manager so must have had some issues or have been very short lived.
Hi Jim - thanks for the info on compiler error if the rotary encoder is not selected.? Now fixed in my version here, will release an update once I have tested a few more of the options in my_SA.h
To all - I plan to change the way the set centre frequency works.? Currently it also adjusts the span to be twice that of the centre frequency.? I would rather the two were independent, so If I have a span of say 5Mhz set, the changing the centre will keep that span (unless it reaches the limits of the possible sweep frequencies), just change the centre frequency.? Also the focus menu command (Sweep/Focus Frequency) currently uses something called FOCUS_FACTOR defined in my_SA.h, so the span changes with frequency, which I find just weird.? I think this should be a fixed span set to give maximum useful resolution, eg 2.6kHz RBW and 290 data points = 754kHz.? This would be defined in my_SA.h as FOCUS_SPAN, so the user could set it as desired.? The span can always be adjusted afterwards of course.? Maybe 1MHz may be more sensible.? The marker Focus function has an extra menu level to select the span - this could also be done for the focus frequency menu item.? How would you like these menu items to work?
73
Dave M0WID
Dave
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Bo, OZ2M
Gyula Molnar