Re: [Discuss-gnuradio] An interesting application for my new USRP... some input requested

[n4hy]

Apologies.  Poor writing.  YOU do not need to insert with the "all 
derived from one source" system.
Others, with multiple LO's etc. can use the injection of known reference 
method.

HF sucks.  It is full of very large signals that will typically hurt 
this kind of system (12 bit front
end).  You have to scale to handle the largest signal and the weaker 
ones go off the bottom, even
after processing gain through the DDC.  If you build filters and 
preamplifiers,  you can hook up
single banded front ends directly to the Basic RX inputs.  These filters 
and preamps do not have
to be super but do need to do some selection, filtering and 
amplification for your work.  Then
you can directly digitize and DDC the RF.  I do not view this as a thing 
you would want to try
with the USRP "directly" hooked  to the antenna.

Bob



John Ackermann N8UR wrote:

> I'm confused by the need to insert a reference signal and resample 
> from that.  I was thinking of just programming the four DACs (through 
> two Basic RX boards) to each look at a, say, 10kHz wide chunk of 
> spectrum around the nominal frequency, and then do a deep FFT of each 
> of those streams.  I'm confused by the need to inject another signal 
> and resample.  I'm sure I'm missing something, but I don't know what...
>
> John
>
> PS -- it may be you're describing what I did in the last couple of 
> FMTs -- insert a known frequency from a signal generator within 100Hz 
> or so of the unknown, then using FFT measure the delta between the 
> two.  That works very well, but requires me to measure only one signal 
> at a time. I was hoping that with the USRP I'd be able to measure all 
> four bands simulateously.
> ----