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
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