Pluto as a Digital Frequency Converter

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G4NZV
Posts: 33
Joined: Wed Mar 24, 2021 8:35 pm

Pluto as a Digital Frequency Converter

Post by G4NZV » Thu Mar 25, 2021 9:33 am

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
Attachments
F1F2 GRC blocks.PNG
F1F2 GRC blocks.PNG (120.02 KiB) Viewed 2222 times
G4FRE 250KS 20210323.PNG
G4FRE 250KS 20210323.PNG (42.11 KiB) Viewed 2222 times
G4FRE 6cm 20210323.jpg
G4FRE 6cm 20210323.jpg (81.05 KiB) Viewed 2222 times

Pa3fbx
Posts: 178
Joined: Fri Oct 16, 2020 1:08 pm

Re: Pluto as a Digital Frequency Converter

Post by Pa3fbx » Fri Mar 26, 2021 9:31 pm

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

G4NZV
Posts: 33
Joined: Wed Mar 24, 2021 8:35 pm

Re: Pluto as a Digital Frequency Converter

Post by G4NZV » Sat Mar 27, 2021 9:23 am

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

M0DTS
Posts: 653
Joined: Sun Feb 24, 2008 9:03 pm

Re: Pluto as a Digital Frequency Converter

Post by M0DTS » Sat Mar 27, 2021 12:53 pm

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

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