[USRP-users] BasicRX front-end advice

Benjamin Woolley ben at legitparty.org
Tue Sep 3 00:31:56 EDT 2013


Hi list,

I am successfully receiving, for example 88.5 KPLU, using an N200 with a BasicRX. I have two antennas directly connected to the RF 1 and RF 2 sockets via a 10 foot cable for each. I tune to 83.8 MHz at 10 Msps, and demodulate 4.7 MHz within that 5 MHz bandwith, ultimately getting the 88.5 MHz signal where I seem to be successfully comparing phase difference between the two antennas.

I just happen to be able to pick up 88.5 despite the 100 MHz ADC aliases, and the 10 MHz sample rate aliases I (correctly?) expect to exist. I am luckily avoiding any major interference. No other station I have tried comes in as clearly, if at all. 

Now, I see that the signal is received on the low end of the samples. In 16 bit signed integer samples, I get values of around 8 of those 16 bits, and this is a high power broadcast signal. It seems that my next task is to improve reception by adding amplification and filtering. 

My next stage is to receive some lower power public transmissions from, for example, public service bands, like 155.580 MHz. But I believe 35 kW to 40 W means I need about 30 dB of gain, or about 10 more bits of signal depth. I can receive these great on a TVRX2, and read phase really well, but with independent local oscillators, the phase difference drifts considerably, and calibration is difficult with these drifting phases. That is why I am reverting to BasicRX's more direct interface. 

Ideally, what I am looking for is to have TVRX2 functionality, but with BasicRX phase properties, as if it use a single oscillator. 

My questions are:
1. Does my approach make sense, to use BasicRX and add some front-end equipment? Am I on the right track?
2. If so, does anyone have any product recommendations for me, someone with primarily software experience, and only a trivial amount of hardware tinkering experience? 

Thank you,

Ben



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