LNB Local Oscillator offset

[pe2bz]

Hi,
I am wondering how SDR Console (v 3.3 ) handles the downconverter settings for by example LNB use, when the LO frequency is higher as the RX frequency.

I have connected (by bias-t) an LNB for the 19.7 to 20.2 GHz range, which has it's LO at 21.2 GHz. How can I tell SDR Console it's 'inversed' ?

The good thing by using a higher LO is , I can try to tune the SDR to a lower range ( below 19.7 GHz) by tuning the SDR to a higher IF, but I would like to be able to see if the IF frequency indeed goes up when I am tuning down. Somehow I think this is (yet) not supported in SDR Console ?

Thanks for your help.

Ben

[Max]

Hi,
I am wondering how SDR Console (v 3.3 ) handles the downconverter settings for by example LNB use, when the LO frequency is higher as the RX frequency.

Ben

I am not 100% sure, but is it not the "Invert Spectrum" option you need to enable in the "Definitions" options when LO is high?

See attached image.

73

Max

[ik8xld]

Hi,
I made a similar request a while ago.

https://forum.sdr-radio.com:4499/viewtopic.php?t=1672

73 Rocco IK8XLD

[pe2bz]

Hi,
I am wondering how SDR Console (v 3.3 ) handles the downconverter settings for by example LNB use, when the LO frequency is higher as the RX frequency.

Ben

I am not 100% sure, but is it not the "Invert Spectrum" option you need to enable in the "Definitions" options when LO is high?

See attached image.

73

Max

Hi Max, thanks for the reply

I overlooked this setting, but the bad news is that does not appear to do what I assumed it to do. I made an excel sheet with the IF I have to tune to and have that subtracted from the local oscillator to calculate the RX frequency. Wiht both the downconverter and invert spectrum enabled I do not see the signals at the expected 19 GHz range when tuning, but they still are around the IF output frequency, but , the spectrum is inversed, as in, I have one "transponder" with moving bandwidth at the left side with the "invert spectrum" off, and that shows the moving bandwidth at the right when "invert spectrum" is on. So the IF output might indeed show the right results now for the LO being higher as the RX frequency , but the signals show not on the expected 19 GHz range.

Any other suggestions ?

Thanks,
Ben

[Simon G4ELI]

So,

If you have a LNB with a LO above the received frequency then:

* What is the LO frequency?
* What is the frequency you are tuned to?
* What is the Converter definition? I expect this should be an Upconverter?

[ik8xld]

Hi Simon,
These are the specifications of a typical C-band LNB.

OL - IN = IF
5150-3400=1750
5150-4200=950

In this case spectrum is inverted.
It is a down converter
it would probably be enough to allow the negative sign in the RX OFFSET field in converter definition

Rocco

[pe2bz]

So,

If you have a LNB with a LO above the received frequency then:

* What is the LO frequency?
* What is the frequency you are tuned to?
* What is the Converter definition? I expect this should be an Upconverter?

I have connected (by bias-t) an LNB for the 19.7 to 20.2 GHz range, which has it's LO at 21.2 GHz.

Converter definition is downconverter , with LO set at 21.2 GHz , I can not see why this should be an upconverter? As far as I know, I am downconverting a GHz range to the IF output range, so downconverting.

Same applies for C-band LNB's which are common for their LO around 5 Ghz.

I am familiair with the downconverter settings for regular satellite LNB's for QO100 and local 3 cm beacon reception, where the LO is belowe the RX frequency. In this case however, A am "stuck"

Thanks,

Ben

[jdow]

I agree there is a nomenclature issue. However, if it works, use it. What term would you use for something that gives an air frequency, Fair = Flo - Fgen compared to Fair = Flo + Fgen. (FLo = local oscillator frequency and Fgen is the generated low frequency signal.) Now I would say "high side converter" and "low side converter"; but, that's a lot of letters wasting space. BUT, to save confusion that might be Simon's best choice.

{o.o}

[pe2bz]

Sorry all, but I still am clueless in what the solution should be.

Start with the dish pointed to "some satellite" at 31,5 West, which actually carries a telemetry beacon.

LNB is RHCP no matter if powered with 12 or 18 volt.

I do the math and subtract the LO of the LNB from the beacon signal from the list.

19.693850 is the TX frequency. So 21.2 GHz LO minus 19.693850 gives an IF output on the LNB of 1.50615 GHz

HackRF as receiver, no (down)converter and no invert spectrum selected, I clearly see the beacon signal in the waterfall.

But in no possible way I can find a converter / invert spectrum setting combination which shows the same signal at 19.693 GHz.

When I choose the converter as upconverter , with the 21.2 GHz LO frequency, it looks like I get the same waterfall every 10 Mhz. I am still convinced that setting the converter as upconverter makes no sense.

If I take an HF upconverter as example, with 100 MHz LO, it makes sense to set it as upconverter, cause the HF (for example 3.6 MHz) I want to tune is mixed up by the converter to 103.6 MHz

With the upconverter setting at 21.2 GHz LO and my wanted RX frequency being 19.694 GHz I should tune to 40.894 GHz ? That never gives me the "real" frequency in the waterfall when using this (or an C-band LNB) with higher LO frequency.

And running the upconverter with these settings I have the same waterfall output in every 10 MHz part of my HackRF.

Thanks again for your time and patience.

Ben