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Re: [Discuss-gnuradio] R820T frequency tuning issue

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] R820T frequency tuning issue
Date: Sat, 28 Mar 2015 11:37:34 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

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 
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 
(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.

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