Re: [Discuss-gnuradio] R820T frequency tuning issue

[Marcus D. Leech]

On 03/28/2015 11:29 AM, address@hidden wrote:
> this is very confusing ... it works. I did upgrade yesterday from gnuradio 
> 3.7.3 to 3.7.5, but
> surely enough both osmocom_fft -f 1575.420e6 -g 30 and a basic flowgraph from 
> gnuradio-companion
> using a 2 MHz sampling rate, osmocom source and WxGUI FFT sink, seem to exhibit 
> stable CW measurements.
> I did unplug the dongle and plug it back into the USB port to make sure the 
> settings had not been
> altered by oscmocom_fft.
> I had to change synthesizers because the Hittite one I was using is on an 
> experiment at this time,
> so I fetched a R&S SMA100 which only goes down to -20 dBm and added 18 dB 
> attenuation. At such a
> level and with 50 dB gain on the RF front end the signal is barely visible when 
> averaging
> (alpha=0.133), but the PLL sure looks like it is locked and exhibiting the 
> expeted -80 ppm offset.
> Sorry for the trouble, will make sure now the issue is indeed solved, and let 
> the measurement run until
> monday morning.
>
> Thanks, JM
Your results are consistent with what I've heard about the R820T above 
1500MHz or so.  It starts to become
  "deaf", and then as you move higher, the PLL won't lock at all.