Satellite dish interface

[Croy9000]

I am working on a hobby project to track signal strength on a DirecTV dish (which wont be connected to a set-top box). These newer dishes have a LNB that can be switched to send one of a few satellites downstream through its RG-6 connection. This switching is done by injecting one of 4 possible combinations of 18V/13V and a 22KHz tone.

I have found a TI eval board containing a chip for doing exactly this: TPS65233EVM. It take Vin (J2), and via I²C, outputs the required voltage/signal on VLNB (J13).

My question is about connecting that 18V/13V/22KHz VLNB output to my circuit. My naive thought is just tapping directly into the RG-6 signal path like this:



I don't do much in the analog domain like this. Can anyone give me tips for any additional considerations (like isolation, impedance issues, etc)? Or should this work fine?

Thanks for any help!

[Gyro]

Pah, in the good old days we used to do it the hard way, we didn't need no chip!  It would have been nice to have a compact and efficient off-the-shelf solution like that though.

That eval board is designed to feed into the LNB supply pin of a satellite tuner inside the STB. Inside the tuner you have the necessary filtering to pass the supply and 22kHz signal onto the RF input without messing up the input impedance or attenuating the signal.

You can probably get way with just a series inductor with a self resonant frequency above the 950-2150MHz IF frequency, probably with a decoupling capacitor between the VLNB and the RG6 shield too (before it  goes through the inductor). One of the RF guys may be able to suggest something a bit more scientific.

If you're wanting to get further into dish positioners, switches and other data then you should make yourself familiar with the DiSEqC spec. You can do a lot more than just the Lo band Hi Band and H/V polarization selection from your 4 states of LNB supply voltage and 22kHz. DiSEqC works by on/off modulating the 22kHz...

https://en.wikipedia.org/wiki/DiSEqC