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RFI Source Identification Signature Storage Application
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Greetings Erik,
? ? ? ?A common problem for radio amateurs is the proliferation of modern day RFI sources that cause significant interference particularly to the HF bands. IMHO a portable low cost spectrum analyzer that includes some specific features intended to support tracking down noise sources would be of significant interest for many hams. ? ? ? ? Often noise sources are related to the power line frequency. It has been well documented elsewhere that because there are often multiple A/C power related RFI sources around the home and within the local hydro grid that an ability to record the time domain signature of the most offending noise is helpful for identifying the most significant cause. Once a problem is located within one's home it can usually be corrected. If a power grid problem is pinpointed it has been experienced that usually the utility will repair it expediently. Spectrum analyzers with time domain signature waveform comparison capability are now used by many utility companies for locating RFI sources. ? ? ? I found it interesting that that the tinyVNA firmware already offers a zero span mode with time domain display capability. I wonder if the time domain display could be designed to lock on to a hydro buzz type of noise and store a few cycles? If this were implemented the offending RFI?waveform signature could be compared to noise sources found in the field to help identify the source. Possibly a split screen display with the stored waveform shown within the top half and real time waveform in the bottom half would offer a convenient means for the user to compare signatures. ? ? ? ?I am interested in evaluating a tinyVNA for the purpose of tracking down RFI sources. Best Regards, Tom, VA7TA |
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Greetings Erik,?
? ? ? ? ? ? ? ?Further to my first message in this thread I have become aware that there are small, inexpensive pocket size battery powered oscilloscopes available with trace storage capabilities. Possibly a small portable scope could work well in conjunction with the tinySA to provide a time domain display with signature storage capabilities. ? ? ? ? ? ? ? ?I wonder if during zero span mode if it would be possible to connect an external scope for time domain viewing the linear amplitude characteristics of the signal being monitored? IMHO it would be a useful feature. Best Regards, Tom, VA7TA |
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Would something as shown in this post help?
/g/tinysa/message/37 The scan speed in zero span can be set but the upper bandwidth of AM demodulation is about 1kHz (maybe 2kHz)? After measuring the scan can be paused and later the tinySA can be connected to a computer to grab the screen I do not yet foresee saving scans to flash as I'm not sure how many flash writes can be endured |
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Internal flash allow minimum 10k write cycles (as in datasheet)
Possibly use external SD card for this, and use simple SPI transfer mode (easy connect to display SPI bus) Transfer modes
Cards may support various combinations of the following bus types and transfer modes. The SPI bus mode and one-bit SD bus mode are mandatory for all SD families, as explained in the next section. Once the host device and the SD card negotiate a bus interface mode, the usage of the numbered pins is the same for all card sizes. ?
SPI bus mode: Serial Peripheral Interface Bus is primarily used by embedded microcontrollers. This bus type supports only a 3.3-volt interface. This is the only bus type that does not require a host license.
One-bit SD bus mode: Separate command and data channels and a proprietary transfer format.
Four-bit SD bus mode: Uses extra pins plus some reassigned pins. This is the same protocol as the one-bit SD bus mode which uses one command and four data lines for faster data transfer. All SD cards support this mode. UHS-I and UHS-II require this bus type.
Two differential lines SD UHS-II mode: Uses two low-voltage differential interfaces to transfer commands and data. UHS-II cards include this interface in addition to the SD bus modes.
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? ? ? ? An analog AM bandwidth of 1KHz would be sufficient for tracking down utility power noise sources which typically generate 100 or 120 Hz fundamentals along with a few harmonics. The amplitude significant harmonics typically fall below 1 KHz. A real time, linear analog amplitude response output for connection of an external scope may be the most practical way to support hydro related RFI source searching. Maybe a filtered PWM output active during zero scan mode might be worth considering. The pocket size scopes which I discovered advertised online have significant trace storage and PC USB interface features. Some interesting models are priced within the $50-$100 range, IMHO not too bad of a financial burden for those serious about using the tinySA for tracking down RFI sources.
Tom, VA7TA |
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As the internal flash can endure above 10k write cycles I assume using the internal flash with a warning not to store too often is OK.
Saving settings to one of the internal memory slots now also saves the stored trace and loading a saved setting will restore the stored trace. This provides 4 memory slots to save traces? |
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Greetings Erik,
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? ? ? ?Here are some additional comments which I hope are helpful:
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? ? ? ?Although the screen view at " /g/tinysa/message/37 " shows a time domain capture of a signal the trace shown would need to be expanded to be useful for RFI signal signature identification. It is apparent the signal amplitude shown in this trace was compressed due to the 10dB/div Y axis scale and that the sweep duration captured too many cycles.? IMHO a linear voltage Y axis scale is necessary for this application to produce a trace similar to what would be obtained by an oscillosope connected to an AM detector output with scope settings as follows:
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? ? ? ? ? ? ? ?- Sweep duration set to capture one or two cycles.
? ? ? ? ? ? ? ?- Vertical sensitivity set so the signal is near full amplitude of the screen.?
? ? ? ? ? ? ? ?- Single sweep triggering with storage to capture the waveform.
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? ? ? With a linear scale mode and appropriate vertical gain the signal would be expanded to cover a much wider range of the Y axis. To expand the X axis signal view the availability of a sweep duration of 20 mS would be desirable for utility power related RFI. A 20mS sweep would provide a view of just a couple of cycles of 100/120 Hz related noise. Should a noise with a fundamental of 50/60 Hz be encountered the 20mS sweep duration would result in a single cycle capture which would still be useful.
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? ? ? ?In addition to a normal sweep trigger mode the availability of a single sweep trigger option would be a significant enhancement. Because of the random inconsistencies of typical RFI noise signals a steady trigger point for repetitive sweep cycles might not be available. A single sweep mode with trace storage would be very useful for capturing a noise signature that could otherwise be blurred by the varying trigger points that very possibly would be encountered using repetitive sweep modes.??
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Best Regards,
Tom, VA7TA |
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Tom,
I already added the ability to have linear Y axis. Triggering is something that makes sense in zero span mode anyway. In the setting/scan speed/point time menu option you can set the time per one of the 290 scan points in microseconds. Shortest time for a full scan is 100mS Will have a look at triggering. |
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A rather basic trigger mechanism is implemented,
If a signal is above a settable level a capture is done. Here a 433MHz RF remote control transmission I need to add some info on the horizontal time scale and decide if it is going to be trigger once or trigger always as now you have to pause sweep to prevent further captures |
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Greetings Erik,
? ? ? ? ? ?Looking good!!! This feature that would permit the screen capture of a sporadic burst IMHO could prove very useful. Terrific that you can do this for both time and frequency domain displays! ? ? ? ? ? ?IMHO if it is practical to implement multiple modes of triggering that would be desirable. Oscilloscopes typically offer Auto, Normal and Single trigger modes. Situations occur where one needs a Single?trigger that captures and holds the view. For recurring cyclic situations Normal? triggering where the capture is repeated each time the trigger point is reached is very useful. Auto?triggering simply provides a recurring sweep mode whether or not a trigger point is reached. Auto is useful for obtaining a trace whether or not there is a signal present which is the typical spectrum analysis mode which you have no doubt already implemented.? Tom, VA7TA |
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On Thu, May 7, 2020 at 01:41 AM, <erik@...> wrote:
As the internal flash can endure above 10k write cycles I assume using the internal flash with a warning not to store too often is OK.At this moment i implement SC Card support for NanoVNA H4, it very simple and good work. Use SPI interface some as display, need only SD_CS,?SPI_MOSI,?SPI_SCLK signals (SPI shared vs display and work on some speed), good if exist SD_CD (for SD card insert); It very low cost solution, need ~7kB flash and ~600 bytes RAM for full dile read/write Fat16/32 support (can extend, use FatFS lib) |
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On Fri, May 22, 2020 at 09:52 AM, DiSlord wrote:
At this moment i implement SC Card support for NanoVNA H4, it very simple and good work. Use SPI interface some as display, need only SD_CS,?SPI_MOSI,?SPI_SCLK signals (SPI shared vs display and work on some speed), good if exist SD_CD (for SD card insert);Dislord, ? ?Will your SC Card support also include transferring stored traces to a PC?? What formats do you anticipate being a to store to the SC Card? - Herb |
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