bypass diplexer

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royae
Posts: 5
Joined: Sun Dec 03, 2017 11:58 am

bypass diplexer

Post by royae » Sun Dec 03, 2017 12:04 pm

Hello !

I have a RTL-SDR V3 dongle.

I would like to sample 2 RF signals ‎simultaneously with it :
- first signal by tuning the RT820v2 tuner and use the I pin ADC of the dongle
- second signal by using the direct sample RF chain of the V3 dongle and the Q pin ADC

Is-it possible to configure the dongle this way ?

I suppose I have to disable the down-converter of the realtek chip, that is get the raw ADC output of the IF (no I/Q transformation) from the I pin and similarly for the second signal on the Q pin.

The second signal would be injected in place of the diplexer that is used for the direct sampling mode. But I don't know where is the diplexer on the board. Where can one find a shematic for the V3 dongle ?

royae
Posts: 5
Joined: Sun Dec 03, 2017 11:58 am

Re: bypass diplexer

Post by royae » Sun Dec 03, 2017 7:40 pm

up : more explanations about my project

rtlsdrblog
Site Admin
Posts: 1874
Joined: Mon Nov 19, 2012 11:54 pm

Re: bypass diplexer

Post by rtlsdrblog » Sun Dec 03, 2017 11:45 pm

Hmm I'm not sure if it's actually possible to get the two ADC branches simultaneously. Though the E4000 chip does use both together so it might be possible, but it would require some investigation of the driver code.

The V3 is already set up so that the R820T signal goes into the I-branch ADC ports, and the HF signal goes into the Q-branch. There should be no need to modify the dongle. If you wanted to inject a signal directly into the Q branch, then juust remove the transformer T2 and connect to the Q-branch breakout holes in the top right.

royae
Posts: 5
Joined: Sun Dec 03, 2017 11:58 am

Re: bypass diplexer

Post by royae » Mon Dec 04, 2017 10:00 am

rtlsdrblog wrote:
Sun Dec 03, 2017 11:45 pm
Hmm I'm not sure if it's actually possible to get the two ADC branches simultaneously. Though the E4000 chip does use both together so it might be possible, but it would require some investigation of the driver code.
I will try that with the help of the datasheets one can find about the realtek chip.
rtlsdrblog wrote:
Sun Dec 03, 2017 11:45 pm
The V3 is already set up so that the R820T signal goes into the I-branch ADC ports, and the HF signal goes into the Q-branch. There should be no need to modify the dongle. If you wanted to inject a signal directly into the Q branch, then juust remove the transformer T2 and connect to the Q-branch breakout holes in the top right.
Cool, thanks for the info.

royae
Posts: 5
Joined: Sun Dec 03, 2017 11:58 am

Re: bypass diplexer

Post by royae » Sat Dec 09, 2017 10:21 pm

remove the transformer T2 and connect to the Q-branch breakout holes in the top right.
Well I have some problem finding those parts on the PCB... Could you please explain a bit more where they are?

rtlsdrblog
Site Admin
Posts: 1874
Joined: Mon Nov 19, 2012 11:54 pm

Re: bypass diplexer

Post by rtlsdrblog » Sun Dec 10, 2017 8:31 am

The transformer is the large component with wire coils on the bottom right (with the USB facing to the right).

Q-branch holes are directly to the left of the LDO. (The wider spread holes)

royae
Posts: 5
Joined: Sun Dec 03, 2017 11:58 am

Re: bypass diplexer

Post by royae » Mon Dec 11, 2017 1:13 pm

OK, got them thanks !

Another question : What is the "easiest" way If I need to inject my signal after the preamp and before the 24Mhz low pass filter (direct sampling rf chain) ?

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