Hi, I’m Carlos, I’m an electronic engineering student at the Industrial University of Santander, Colombia.
I am doing a social project related to Othernet to provide academic and learning material for areas of the country without internet access
Would anyone be kind enough to provide me with a schematic circuit of the LNB?
I enclose the block diagram.
You will find texts in your university library with schematic examples for making a low noise amplifier and a bandpass as well as a frequency downconverter. You need to remember though that at 11GHz you are already into the frequency zone where circuit board layout must be designed properly to prevent accidental coupling of components capacitivly or an unintended inductor in the traces and components cancelling out your signal. This microwave circuit design difficulty is why we downconvert into an easie to use UHF signal and then send that down the feedline.
Read these Wikipedia articles to find the sources you need
One thing your block diagram doesn’t include is a bandpass to split off the DC power supplied through the coaxial cable.
So far I see othernet supplying inexpensive commodity LNBs which have been tested for use with the satellite transmitting in the user’s area.
I think, The dual band lnbf that is currently shipping with also adds the 22khz detection on the receiver coax to shift the local oscillator from 9.75GHz to 10.6GHz. How this is accomplished… I don’t know.
Some of the lnbf’s also have two antenna elements (90 degrees rotated) to allow either “vertical” or “horizontal” reception … not exact since rotating the lnbf also skews the orientation. Many are selected based on dc voltage (for example 13vdc or 17vdc)
I think the term used on a satellite transponder is useful, they call it a bent pipe, as in it(the low noise amplifier stage) receives a band of so much khz or mhz(depending on design) and retransmits it on another band. The dual band LNB does the same thing, I assume you mean that it will downconvert either/both bands down to the same frequency, overlayed upon each other. Just treat the signal we squirt down our feed cable which is the same encoding as found on that higher band, as received just downconverted; pretty much the same as when a radio tuner throws the signal at the mixer and leaves you with the IF.
As for the polarity it isprobably just two antenna wires or PCB traces to two pins attached to two LNAs inside an IC with voltage detection for polarity to decide which LNA/antenna/pin circuit to choose.