USRP 2932 For GNSS Receiver

[NitinSharma]

Hi All 

I am using USRP 2922/2932 to record GNSS signals. I could get some Signals while recording GPS using USRP 2922.. I am using active antenna 20 dB gain + Bias Tee + external LNA 13 dB gain.. This works fine sometimes (only 1 out of 100 or more). I was able to acquire few GPS satellites but was not able to get preambles in them (No navigation data). I used RF record and Play back VI with 1.57542 G as Carrier frequency 25 dB gain, 10000 as write buffer setting and 4 MSPs settings. I am not sure whether this VI receives data continuously or not? If it can receive data continuously why I am not able to get any Preamble even in 20 GB of data.  While it shows good acquisition results (attached herewith). I hope USRP is capable of continuous recording? Do I need to explicitly mention somewhere to select active GPS antenna connected in Rx1 port?

The data was recorded in I16 format, which need lot of disk space and time to process. USRP 2932 specification says we can use it in I8 mode also.. However, I am not able to find any details about how we can record data in I8 format. Even few details mentioned in some other similar post are not very clear. As I am not able to find any I8 mode in property node of USRP. niUSRP property node has no option of I8 as far as I tried. I tried using data typecasting from I16 to I8 but it subtracts 256 from all I16 samples only.. I do not know how that will be useful and I do not think it is correct.. can any one help in getting records in I8 format also how to record GPS data using USRP 2922  or 2932.. how much external gain will be required for the same..? How I can increase bandwidth of my recording to 20 MHz or more?