X Band LNB

X-bander · 1. April 2022

Hello all,

I'm tuning in a little late for the party. Hope the thread's still active. Have a few questions and concerns... I'm relatively new to this field. Perhaps femi, @strannik and s-band could help.

I have a 2.4m meshed dish, and I'd like to have an LNB to downconvert signals in the vicinity of 7.5-8.4 GHz frequency range, for some software defined radio experiments. Now, it is my understanding that this is not a trivial task, and I was wondering what components I would need specifically. Making them wouldn't be a problem..

If the budget is not an issue, would it be possible to have a rig that could cover the whole range in one go, or would I need a few extra components? For instance, my naive interpretation would suggest that I would only require a dish, an LNB with RF input of 7.5-8.4 GHz (which seemingly is not off the shelf) and then a dongle which would have the right IF input. If this isn't the case, I'm truly curious as to why this wouldn't work..

Would I need to have a Dish - waveguide - polarizer - lnb - dongle ?

Cheers,

X-bander

femi · 1. April 2022

Es gibt hier leider wie im Ka-Band verschiedene Frequenzbereiche wie 7,25-7,75 GHz 7,75-8,5 GHz.

Das größere Problem ist aber das Feed. Selbst wenn du eines findest, stehst du vor der Herausforderung es so zu Positionieren, dass der Brennpunkt stimmt.

Für das LNB solltest du einen vierstelligen Euro Betrag einplanen, Das Feed fällt auch nicht unter Low Budget.

Was den Dongle betrifft, musst du dich mit den SDR Leuten unterhalten.

Der Ausgang ist wie bei anderen LNBs im L-Band. Je nach sonstigen Equipment bekommt man sie auch mit N- oder SMA-Anschluss (50 Ohm).

Überlege dir die Kosten/Nutzen sowie den Aufwand, wäre ja nicht so billig, wenn man in der Mitte dann wo steckt.

Unfortunately, as in the Ka band, there are different frequency ranges such as 7.25-7.75 GHz and 7.75-8.5 GHz.

But the bigger problem is the feed. Even if you find one, you face the challenge of positioning it so that the focal point is right.

You should plan a four-digit euro amount for the LNB. The feed also does not fall under low budget.

As for the dongle, you need to talk to the SDR people.

The output is like other LNBs in L-band. Depending on the other equipment, you can also get them with an N or SMA connector (50 ohms).

Think about the costs/benefits and the effort, it wouldn't be so cheap if you were somewhere in the middle.

**s-band** · 3. April 2022

Hi X-bander, welcome to the forum. It depends on what you are hoping to get out of it.

7.25-7.75GHz - mainly geostationary milsat with little that can be demodulated to give more than an SNR and signal information. Mostly LHCP.

7.5-8.4GHz - Earth observation (weather satellites etc) Some geo some LEO/MEO. Many can be received using SDRs but the bandwidths are high so you'd need a LimeSDR or Ettus/NI with 50Ms/s or thereabouts.

8.4-8.5GHz - Deep space (DSN), most RHCP. You might just be able to demodulate some craft close to Earth but most people with small dishes (<10m) make do with detecting the carriers. The whole RX chain needs to be GPS locked or using something like a rubidium standard or better (you're looking for signals in 1Hz bandwidth sometimes). For most things Airspy, Pluto etc SDRs are fine.

For anything except the geo satellites, you'll need full a az-el mount for the dish in order to track them. A TV card is OK to lock a lot of the Milsat stuff but many people use GnuRadio weather and DSN demodulation. SDR#, HDSDR etc are the easiest to use for simple detection and IQ capture of narrower signals.

As femi said, X band covers a large frequency range. It is possible to cover it all with one set-up but there will be compromises. I use a wide band LNA that covers 7-9GHz and feed that, via a low loss cable, to the equipment indoors. I started by using a rats nest downconverter built from Ebay parts. I now use a spectrum analyser with its IF fed to the SDR (Airspy, Pluto, RX-888) for the narrower signals and the down converters if for wide band (inc Milsat). I usually use the home made 8.4GHz feed and de-polariser. That just about works OK down to 7GHz but the the polarisation is not defined below about 8.3GHz. It's fine for the strong milsat stuff and I have received echoes from the 7GHz uplinks to Lunar craft.

There's a range of equipment shown earlier in this thread varying from high end pro to my scrappy home made stuff. The notes above are only based on my random experimentation and there may be better options;-) What do you want to receive?

X Band LNB

qwer 19. August 2022

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