[USRP-users] TVRX2 Automatic Gain Control problem

Marcus D. Leech mleech at ripnet.com
Wed Jun 20 23:19:08 EDT 2012

> Hi Marcus,
> Firstly, i would like to thank you for the info about the AGC 
> configuration and the TDA datasheet. However i'm now worried with that 
> you've said about the use of two TVRX2.
> "Also, keep in mind that only a *single* TVRX2 can be used per USRP1 
> due to I2C addressing limitations."
> This is weird, because in fact i'm using two TVRX2 in one USRP1 and i 
> can tune both boards, although the tuned frequency for both TVRX2 
> channels (RX1 and RX2) is mirrored for both boards on the RXA and RXB 
> slots. This would not be a problem for my application because i really 
> need that all RX channels from both boards be tuned at the same frequency.
> On Gnuradio, i can see the four channels receiving radio signals on 
> the tuned frequency (each channel is connected in a different antenna) 
> and using the uhd_usrp_probe command i can obtain the ID from both 
> boards, each in their correspondent slots. Presume this happens 
> because of the data stored at the EEPROM memory in each board.
> Now my doubt is: Am i getting the two TVRX2 channels tuned each time i 
> set the central frequency for both boards? Or one of the boards isn't 
> communicating and it's tuned because the central frequency is stored 
> in EEPROM memory and read by the TDA receivers when USRP1 and TVRX2 
> boards are turned on?
> Cordially,
There is no frequency or parameters information stored in the EEPROMs.   
I'm rather surprised that this is working apparently-sanely.
   Which may purely be by accident.  There is insufficient I2C address 
demuxing on the the TDA18272 chip, so you can only have two of
   them on any given I2C bus, and the USRP1 only has a single I2C bus.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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