[Discuss-gnuradio] Re: USRP at Ham Field Day

[John Ackermann N8UR]

John Ackermann N8UR wrote:

> Good job on the hfexplorer software, Chuck!  Just a couple of
> suggestions:  (a) trying to tune in broadcast stations on AM resulted in
> horrible distortion -- sounds like extreme overload and clipping; 

I just tried putting an AM signal into the USRP + BasicRX +
hf_explorer_9a and found a problem with the AM demod.

Putting in a signal with 30% modulation @ 1kHz at a signal strength of
up to about -55dBm (which shows about +15dB on the FFT) sounds just
fine, though there's a bit of hiss.  But when you increase the signal
strength to ~-53dBm (501uV), it's as though an oscillation breaks out --
you hear another somewhat distorted tone along with the received signal,
and the level of that tone increases rapidly until at about -48dBm
(890uV) it maxes out, with quite a bit of distortion.  The increase
between those two levels is almost a step function, it's that rapid.

John