On 11/03/2020 02:54 PM, Jason Roehm via USRP-users wrote:
On 10/14/20 2:41 PM, Marcus D. Leech via USRP-users wrote:
On 10/14/2020 01:28 PM, Jason Roehm via USRP-users wrote:
I have an N320 that I'm trying out for the first time. I'm using UHD
4.0.0, and I loaded the corresponding root filesystem data for that
release to the N320. I find that when the receiver is tuned to
frequencies below 450 MHz, the spectrum is inverted. When you tune
to 450 MHz or above, the spectrum is upright as expected. See the
attached screenshots for example spectral plots.
There are several ATSC signals visible in the spectrum. I simply
used an indoor antenna, so there is a lot of multipath on the
signals causing their spectra to be very non-flat, but the telltale
sign of spectral inversion here is where the pilot tone is appearing
on each one. In the first plot, tuned to 440 MHz, they appear on the
right of each signal; this is not where they should be. When you
tune to 450 MHz, the location of the signals flip to the right half
of the plot, and the pilot tone is on the left, where they belong.
Is this a known issue?
Thank you.
Jason
I'm discussing this with R&D right now. It's *conceivable*, because
there's an extra mixer stage in the below-450-mhz pathway, and that
mixer stage uses "high side" LO injection, which would produce an
inverted spectrum, but the FPGA would "know" this and invert it back...
Marcus,
Did you ever get any resolution on this issue?
Jason
I've raised the issue with R&D, but not heard back. I'm hampered by not
having an N320 in my own lab to test this.
Presumably, the issue you see is version independent?
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