Universal LNB + SDR

[ImmortalBee]

I've been playing around with a simple total power receiver using a Universal Astra LNB+sat finder meter and offset satellite TV dish. So far I've been content carrying out basic drift scans of the sun and reading the meter at fixed intervals, but recently I've been considering where to go next. I'd really like a better way of recording, and my original plan was to connect a multimeter across the back of the sat finder and record the voltage but recently I read about connecting the LNB to an SDR (e.g. here).

The problem is that the guy above is from the US, where standard LNBs have a single band 12.2 GHz - 12.7 GHz whilst the UK Universal LNB I have has high and low bands which are shifted by different frequencies and hence the intermediate frequency ranges overlap. I'm not at all knowledgeable about RF things, but the IF frequency ranges do not overlap entirely and the region 10.7-10.85 GHz is the only region downconverted to 950-1100 MHz. This suggests to me that I should be able to observe at this frequency, but are there any issues (e.g. electronic or oddities of the FFT) that will mean that the superposition at the higher intermediate frequencies will affect the lower intermediate frequencies?

 

(Apologies for being a RF noob, I'm sure there's a really simple reason why something won't work )

[Carl Reade]

Hi not sure what way the USA LNBs work but firstly all outputs on UK LNBs require power so you will need to add a bias tee the same as Cotos thread before connecting to the sdr.

The sat meter buzzer wires provide a voltage based on the signal strength so you need to connect them to an ADC then to the pc.

You can get volt meters with data loggers built in to connect to a pc.

You could use an Arduino board  to pc which has built in ADC to measure up to 5V more with a resistor inline.

You could use a purpose made ADC.

Ref the LNB you may want to look at the Sky Q new type which is totally different to the universal type. Sky have done away with the high/Lo band IF and now use just horizontal/vertical over an IF band 230Mhz right through to 2300Mhz.

Carl

[robin_astro]

1 hour ago, ImmortalBee said:

the UK Universal LNB I have has high and low bands which are shifted by different frequencies and hence the intermediate frequency ranges overlap.

The LNB only operates on one band or the other at any given time, depending on a 22kHz tone being present or absent so assuming you are not applying the tone, your nominal frequency range (depending on the filtering in the LNB) is 10.7-11.7GHz  mixed down to 950-1950MHz by the 9.75GHz LO.   

https://en.wikipedia.org/wiki/Low-noise_block_downconverter#Universal_LNB_("Astra"_LNB)

Cheers

Robin

[ImmortalBee]

17 hours ago, Carl Reade said:

Hi not sure what way the USA LNBs work but firstly all outputs on UK LNBs require power so you will need to add a bias tee the same as Cotos thread before connecting to the sdr.

...

You could use an Arduino board  to pc which has built in ADC to measure up to 5V more with a resistor inline.

 

Thanks for the advice.

I actually like the sound of the arduino. Previously I assumed I'd use a multimeter, except my current one cannot be connected up to a PC and logging ones are pretty expensive. The arduino method sounds cheap and like it would keep me entertained for a while before I move onto getting a spectrum with an SDR.

 

16 hours ago, robin_astro said:

The LNB only operates on one band or the other at any given time, depending on a 22kHz tone being present

Ah I see. Thanks.