en:sdrx
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en:sdrx [2013/07/26 05:33] – [The LO calibration] fluktuacia | en:sdrx [Unknown date] (current) – external edit (Unknown date) 127.0.0.1 | ||
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==== Verified software ==== | ==== Verified software ==== | ||
* [[http:// | * [[http:// | ||
- | * [[http:// | + | * [[http:// |
* [[http:// | * [[http:// | ||
+ | * [[https:// | ||
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===== Noise interference problems ===== | ===== Noise interference problems ===== | ||
- | Some uses experience miscellaneous difficulties with unwanted interference during the measurements. This chapter summarizes some experiences with the most commonly occurring types of interferences and the possible solutions. | + | Some users experience miscellaneous difficulties with unwanted interference during the measurements. This chapter summarizes some experiences with the most commonly occurring types of interferences and the possible solutions. |
- | At first, let us see the picture of correctly set receiver without the connected antenna and equipped with " | + | At first, let us see the picture of a correctly set receiver without the connected antenna and equipped with a " |
- | {{: | + | {{: |
- | Notice the increased signal in the middle (at zero audio frequency), that is caused by the line frequency (of 50Hz) __(?utility / mains )__ induction in audio cables connected to the sound card. By improving the position the cables and ground loop, further reduction is possible. | + | Notice the increased signal in the middle (at zero audio frequency), that is caused by the line frequency (of 50Hz) __(?utility / mains )__ induction in audio cables connected to the sound card. By improving the position the cables and the ground loop, further reduction is possible. |
The next picture shows the case of antenna connected in relatively RF-free environment. | The next picture shows the case of antenna connected in relatively RF-free environment. | ||
- | {{: | + | {{: |
- | Now we are getting to circumstances, | + | Now we are getting to the circumstances, |
- | We will illustrate the problems using the assembly (shown in the picture below), that cannot be generally considered a good idea to use if we are aiming for a minimal noise interference. The notebook with a plastic cover has a minimal capacity to attenuate the radiated energy. There are lots of AC adapters and long, poorly shielded cables on the table. | + | We will illustrate the problems using the assembly (shown in the picture below), that cannot be generally considered a good idea to use, if we are aiming for a minimal noise interference. The notebook with a plastic cover has a minimal capacity to attenuate the radiated energy. There are lots of AC adapters and long, poorly shielded cables on the table. |
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==== Ethernet over copper ==== | ==== Ethernet over copper ==== | ||
- | One of the most obvious reasons for interference is the switched on ethernet. It is characterized by its thin periodic spectral lines with highest density in the region around 25MHz. | + | One of the most obvious reasons for interference is the switched on Ethernet. It is characterized by its thin periodic spectral lines with highest density in the region around 25MHz. |
The picture below illustrates such state quite clearly: | The picture below illustrates such state quite clearly: | ||
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{{: | {{: | ||
- | There are more solution | + | There are more solutions |
=== Shielding === | === Shielding === | ||
- | The conventional [[http:// | + | The conventional [[http:// |
{{: | {{: | ||
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{{: | {{: | ||
- | You can see, that there are sill a lot of Ethernet caused artifacts in RF signal. They can, however, be attributed mostly to the transmission of parasitic signal through the power cord into the same outlet, that powers the SDR receiver. | + | You can see, that there are sill a lot of Ethernet caused artifacts in RF signal. They can, however, be attributed mostly to the transmission of a parasitic signal through the power cord into the same outlet, that powers the SDR receiver. |
- | If you connect the converter to an other outlet, the interference will significantly decrease in strength. | + | If you connect the converter to another |
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{{: | {{: | ||
- | It would be certainly possible to proceed further with similar measures. To add the ferrite to all of the cables, to separate the outlets, to enclose the receiver with a box, etc. | + | It would certainly |
==== SMPS ==== | ==== SMPS ==== | ||
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The MDS of -120dbm on 150MHz. | The MDS of -120dbm on 150MHz. | ||
- | Towards the lower frequencies it increases, toward higher it decreases. | + | Towards the lower frequencies it increases, toward |
==== Image frequency rejection ==== | ==== Image frequency rejection ==== | ||
- | The minimal and easily achievable | + | The minimal and easily achievable image frequency rejection |
The image frequency rejection must be trimmed for each band separately, since it depends on detuning of the phase of mixer switching and for different frequencies the detuning can vary. | The image frequency rejection must be trimmed for each band separately, since it depends on detuning of the phase of mixer switching and for different frequencies the detuning can vary. | ||
- | The effect of the temperature on settings is not extensive and so it is possible to create a correction table for all operating bands. Some software tools (like Linarad) are able to create such table automatically after the calibration is running and proper generator is connected to the receiver' | + | The effect of a temperature on settings is not extensive and so it is possible to create a correction table for all operating bands. Some software tools (like Linarad) are able to create such table automatically after the calibration is running and proper generator is connected to the receiver' |
=== Image frequency rejection settings === | === Image frequency rejection settings === | ||
- | An interesting method involves the use of linearly modulated signal, that creates a " | + | An interesting method involves the use of linearly modulated signal, that creates a " |
==== Electromagnetic interference ==== | ==== Electromagnetic interference ==== | ||
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===== FAQ ===== | ===== FAQ ===== | ||
- | * Can I power the receiver with +/-10V? The signals on output reach amplitudes of the order of 10-100mV max. Why is than necessary to have such wide power supply range? | + | * Can I power the receiver with +/-10V? The signals on output reach amplitudes of the order of 10-100mV max. Why is than necessary to have such a wide power supply range? |
- | The wide power supply range is necessary, because as soon as a strong signal reaches NF band, it must not cause saturation | + | The wide power supply range is necessary, because as soon as a strong signal reaches NF band, it must not cause saturation |
- | * Why is there no integrated voltage | + | * Why is there no integrated voltage |
- | The stabiliser | + | The stabilizer |
* Do I have to power the receiver with +/-12V supply? Is the +/-10 not enough? | * Do I have to power the receiver with +/-12V supply? Is the +/-10 not enough? | ||
- | The receiver can be powered even with +/- 5V. If you're planing to use the receiver in a portable mode, we recommend the Li-ion batteries in pair for every branch, making the total power supply of +/- 7,4V, which should be sufficient for most applications outside | + | The receiver can be powered even with +/- 5V. If you're planing to use the receiver in a portable mode, we recommend the Li-ion batteries in pair for every branch, making the total power supply of +/- 7,4V, which should be sufficient for most applications outside the town (without strong signals). The accumulators in notebook batteries (of typical size 18650) are mostly suitable. The decreased capacity of old batteries does not matter, because the receiver' |
* Why does the receiver have I and Q output? Can I use the mono input of the sound card for signal digitization? | * Why does the receiver have I and Q output? Can I use the mono input of the sound card for signal digitization? | ||
- | The low-frequency signal from the receiver has I/Q format, so it can include the full input high-frequency signal data. It is basically a vector format, that can be demodulated in principle by any modulation with bandwidth lower than is the bandwidth of A/D conversion. [[http://cs.wikipedia.org/ | + | The low-frequency signal from the receiver has I/Q format, so it can include the full input high-frequency signal data. It is basically a vector format, that can be demodulated in principle by any modulation with bandwidth lower than is the bandwidth of A/D conversion. [[http://en.wikipedia.org/ |
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- | {{ : | + | {{ : |
The radioastronomy is quite perspective field for the deployment of this receiver and a large portion of research is currently devoted to it. | The radioastronomy is quite perspective field for the deployment of this receiver and a large portion of research is currently devoted to it. | ||
- | It's also good to point out, that amateur astronomers have a greater chance of success in the field of radio- than optic astronomy. In order to get results, radioastronomers need a lot of stations over a large area and that is easier to achieve for independent individuals than for organisation. | + | It's also good to point out, that amateur astronomers have a greater chance of success in the field of radio- than optic astronomy. In order to get results, radioastronomers need a lot of stations over a large area and that is easier to achieve for independent individuals than for organization. |
- | An example of project, that supports this notion is eg. [[http:// | + | An example of a project, that supports this notion is [[http:// |
===== Radio meteor detection stations ===== | ===== Radio meteor detection stations ===== | ||
- | The receiver is suitable for use in the radio meteor detection network, as is the case of several observatories in CR. [[http:// | + | The receiver is suitable for use in a radio meteor detection network, as is the case of several observatories in CR. [[http:// |
{{: | {{: | ||
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====== Ideas for improvements ====== | ====== Ideas for improvements ====== | ||
- | * <del> To add a logarithmic scalar output indicating "the extent | + | * <del> To add a logarithmic scalar output indicating "the extent of the receiver's saturation". </ |
- | * To add a module with a suitable ADC and so eliminate the complications with the funcioning | + | * To add a module with a suitable ADC and so eliminate the complications with the functioning |
- | * <del> To desing | + | * <del> To design a module with a galvanically separated symmetrical power supply. </ |
* To figure out a way to compare the gain between the individual receivers. (preferably digitally) | * To figure out a way to compare the gain between the individual receivers. (preferably digitally) | ||
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Adding more modules to the arrangement could create a complete set where the receiver would be independent on a computer. Its realisation has several variants: | Adding more modules to the arrangement could create a complete set where the receiver would be independent on a computer. Its realisation has several variants: | ||
- | * The receiver with a tunable oscillator and module with LDC that would show the tuned frequency. The buttons below the LCD would allow the retuning of the receiving frequency. | + | * The receiver with a tunable oscillator and a module with LDC that would show the tuned frequency. The buttons below the LCD would allow the retuning of the receiving frequency. |
- | * A second variant would be the same as the first one, with an exception of digitising | + | * A second variant would be the same as the first one, with an exception of digitizing |
====== UHF SDR SDRX02A receiver ====== | ====== UHF SDR SDRX02A receiver ====== | ||
- | **The design of the receiver described below is still only in preliminary stage of development** | + | **The design of the receiver described below is still only in a preliminary stage of development** |
- | The design should probably be even more modular. That includes separate VGA input amplifier, input band-pass filter, I/Q demodulator with input band-pass filter. | + | The design should probably be even more modular. That includes |
- | ACD with parallel anti-alias filter and FPGA with parallel USB interface. | + | ACD with a parallel anti-alias filter and FPGA with a parallel USB interface. |
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**The design of the receiver described below is still only in preliminary stage of development** | **The design of the receiver described below is still only in preliminary stage of development** | ||
- | The design should include separate input amplifier (VGA), input band-pass filter to limit the possible intermodulation, | + | The design should include |
- | Analog Frond End ADC with input anti-alias filter and FPGA with PCIe interface for connection to the thunderbolt module. | + | Analog Frond End ADC with input an anti-alias filter and FPGA with a PCIe interface for connection to the thunderbolt module. |
en/sdrx.txt · Last modified: 2013/12/07 11:20 (external edit)