Hi all

Can someone please provide me with some guidance? We are working on a

passive radar project and the aim is to implement a pcl radar receiver

on the USRP1 using TVRx daughterboards. I have the Microtune 7901.

I did some tests to see what the effects of the RF and IF amplifiers

in the tuner are (linear region,etc.). I noticed that the maximum

output of the TVRx is -15dBm regardless of the input signal and the

gains. For this measurement, I’ve got the test circuit that they have

in the Microtune datasheet with the Minicircuits RF transformer to

match the 200 ohm output of the TV tuner to 50 ohms. Also, I captured

a signal from the TVRx and looked at it in Matlab. The maximum I

value is 17 and the maximum Q value is 16, which means that we are not

close to using the whole dynamic range.

I also did a test with the BasicRx db. This time I injected a 13dBm

signal into RX-A. The maximum value in Matlab is 7919 which looks

much better.

Now I have 2 questions:

-Does anyone know anything about the TVRx and why I only get an output

of -15dBm? The Microtune datasheet is a bit vague. It only says that

the signal level for 1dB RF gain compression is 72dBuV (-113dBm) with

AGC deactivated. Maybe the TVRx wasn’t designed to utilise the entire

dynamic range of the ADC??

-What is the maximum signal level after the DDC+filtering,etc? My

guess is around 2047*8 because of the bit-shifting at the ADC

interface.

Sebastiaan

–

Sebastiaan H.

Radar and Remote Sensing Group, University of Cape Town

Tel: +27 83 305 5667