Pluto as a Digital Frequency Converter
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This forum is run by the BATC (British Amateur Television Club), it is service made freely available to all interested parties, please do not abuse this privilege.
Thank you
Pluto as a Digital Frequency Converter
Pluto maybe used as a Digital Frequency Converter to move a chunk of spectrum up to ~2.5MHz bandwidth from one band to another. This example shows reception of a 8Degree sidelobe of a 6cm DATV DVBS2 transmission from G4FRE over a 17.5Km path between Malvern and Tewkesbury using a Portsdown4 and Minituner tuned to ~2322.5MHz.
The technique of shifting chunks of spectrum is very useful as it opens up possibilities of DATV reception on frequencies outside the tuning range of the Serit tuners used in various projects.
Degradation of signal was crudely assessed by converting the QO-100 beacon IF from a non-locked LNB at ~742MHz to 2322.5MHz improving the MER by ~0.4dB.
The GUI shows the spectrum display of G4FRE's 5762.5MHz signal, blue line is the live spectrum, green line is with the maximum hold function enabled. (This is very useful in peaking the dish as the 'best' can be easily observed). If '0Hz offset' is selected a receive frequency can be directly entered otherwise it serves as an offset for fine tuning.
Caveats on this technique are:
- Certain frequencies will not work e.g. When the RX and TX are close together, when the RX is a multiple of the TX
- Band Pass Filters maybe needed for reception in some circumstances
- Approx. 30dB of attenuation is needed between the Pluto TX output and the Serit tuner input
- If the TX output is connected into an antenna then it should be remembered that the whole of the bandwidth converted will be transmitted plus harmonics
I used GRC v3.7 with gr-iio blocks on a i5 windows10 PC
Steve G4NZV
The technique of shifting chunks of spectrum is very useful as it opens up possibilities of DATV reception on frequencies outside the tuning range of the Serit tuners used in various projects.
Degradation of signal was crudely assessed by converting the QO-100 beacon IF from a non-locked LNB at ~742MHz to 2322.5MHz improving the MER by ~0.4dB.
The GUI shows the spectrum display of G4FRE's 5762.5MHz signal, blue line is the live spectrum, green line is with the maximum hold function enabled. (This is very useful in peaking the dish as the 'best' can be easily observed). If '0Hz offset' is selected a receive frequency can be directly entered otherwise it serves as an offset for fine tuning.
Caveats on this technique are:
- Certain frequencies will not work e.g. When the RX and TX are close together, when the RX is a multiple of the TX
- Band Pass Filters maybe needed for reception in some circumstances
- Approx. 30dB of attenuation is needed between the Pluto TX output and the Serit tuner input
- If the TX output is connected into an antenna then it should be remembered that the whole of the bandwidth converted will be transmitted plus harmonics
I used GRC v3.7 with gr-iio blocks on a i5 windows10 PC
Steve G4NZV
- Attachments
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- F1F2 GRC blocks.PNG (120.02 KiB) Viewed 2607 times
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- G4FRE 250KS 20210323.PNG (42.11 KiB) Viewed 2607 times
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- G4FRE 6cm 20210323.jpg (81.05 KiB) Viewed 2607 times
Re: Pluto as a Digital Frequency Converter
Nice,
I still struggle with gnu radio to understand the simple thing of getting it to work for me..
I see ideas of DATV relays 70cm in and 13 cm out using a pluto and a raspberry.
Any chance you create some image for a RPi to download and start easy?
Best regards Benno
I still struggle with gnu radio to understand the simple thing of getting it to work for me..
I see ideas of DATV relays 70cm in and 13 cm out using a pluto and a raspberry.
Any chance you create some image for a RPi to download and start easy?
Best regards Benno
Re: Pluto as a Digital Frequency Converter
I like the idea of using a Raspberry Pi4 & Pluto as a Digital Frequency Converter and I am working on a solution.
However, there is still an unresolved issue when using the Pi4 in that the TX output spectrum has discontinuities. IF the Pi4 work is successful I am happy to share the .grc file and will investigate the possibility of providing an image.
Steve G4NZV
However, there is still an unresolved issue when using the Pi4 in that the TX output spectrum has discontinuities. IF the Pi4 work is successful I am happy to share the .grc file and will investigate the possibility of providing an image.
Steve G4NZV
Re: Pluto as a Digital Frequency Converter
Yes this works well.
You can make some very sharp filters in software to remove unwanted signals close in to the desired one, like we have on 2m and 70cm for example.
Rob
You can make some very sharp filters in software to remove unwanted signals close in to the desired one, like we have on 2m and 70cm for example.
Rob
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Re: Pluto as a Digital Frequency Converter
This thread needs greater exposure as a very handy way of shifting Non-Serit frequencies (9 & 6cms at least) into range.
I wonder if it would run OK on a RPI4 or 5, so you could do away with all that pesky downconverting, LOs, filters etc.....
Although to TX DATV on 6cms you either need to upconvert or usa a laptop/PC and DATV Easy 2.17, so it might as well run on a PC....don't suppose even a RPI5 would manage the work of DATVEasy 2.17...
Gareth (currently doing it the LOs, filters etc way...)
I wonder if it would run OK on a RPI4 or 5, so you could do away with all that pesky downconverting, LOs, filters etc.....
Although to TX DATV on 6cms you either need to upconvert or usa a laptop/PC and DATV Easy 2.17, so it might as well run on a PC....don't suppose even a RPI5 would manage the work of DATVEasy 2.17...
Gareth (currently doing it the LOs, filters etc way...)
Re: Pluto as a Digital Frequency Converter
I have just bought a raspberry pi 5 8Gb and can confirm that GNU radio companion seems to work well on it. It used to struggle when running on a raspberry pi 4.
I did a quick test running a simple frequency converter and it appeared to work OK.
Benno, to get this working I did the following...
Create a SD card using the raspberry pi imager utility. Selecting the 64 bit recommended Raspberry Pi OS.
Boot the RP5 to the desktop then use 'add programs' to search for everything that includes the word GNURadio. Select all of the results and install them. It may not be necessary to install everything but it probably doesn't do any harm.
GNURadio Companion will then appear in the programming menu and will support both Lime and Pluto.
As it works fine from the desktop environment it should also be possible to build a stand alone version that would work without a monitor.
If I get the time I may investigate if Langstone can be made to work on the RP5. At the moment is won't work because the framebuffer on /dev/fb0 is not available on the standard build.
Colin G4EML
I did a quick test running a simple frequency converter and it appeared to work OK.
Benno, to get this working I did the following...
Create a SD card using the raspberry pi imager utility. Selecting the 64 bit recommended Raspberry Pi OS.
Boot the RP5 to the desktop then use 'add programs' to search for everything that includes the word GNURadio. Select all of the results and install them. It may not be necessary to install everything but it probably doesn't do any harm.
GNURadio Companion will then appear in the programming menu and will support both Lime and Pluto.
As it works fine from the desktop environment it should also be possible to build a stand alone version that would work without a monitor.
If I get the time I may investigate if Langstone can be made to work on the RP5. At the moment is won't work because the framebuffer on /dev/fb0 is not available on the standard build.
Colin G4EML