On 13/11/2023 05:08, Steve Hamn wrote:
Hello,
Does the Ettus N320 employ any type of AGC? If so is there a detailed
description of it anywhere? Or can it be disabled?
I don't believe the N320 implements any type of AGC.
I notice that if I send in a strong signal the digital output from the
SDR is approx +/-1. If I send in a weak signal it's also +/-1 just
noisier. I've been experimenting with sending in amplitude modulated
pulses. Seems like over 'long' timescales there is some sort of
automatic adjustment going on that is corrupting my measurements. What
am I missing here?
A narrowband signal right at the tuning center can get modified by the
built-in DC offset compensation in the DSP logic
in the radio. Look into "offset tuning":
https://files.ettus.com/manual/page_general.html
And the API bits here:
https://files.ettus.com/manual/structuhd_1_1tune__request__t.html
The idea is that you ask the radio to offset the LO away from the DC
anomaly, and then the DSP in the radio shifts the bandwidth
so that you get exactly the desired center frequency that you asked for.
What do you mean by "weak" and "strong" signal. The maximum recommended
input to the radio is -15dBM, and its narrowband
MDS at max gain is probably somewhere south of -120dBm. So both
your "weak" and "strong" signals may just be clipping, or
you're mis-interpreting the data that you are collecting. The radio
really does have a quite high dynamic range, but it
does not implement AGC as far as I know. That would be something
you'd have to implement in your signal processing flow.
Conversely it appears I am able to control the TX signal by just
sending out smaller numbers, and I don't see this (or am I just
missing it)?
Thanks in advance for any help or insight you can provide!
Thanks,
Steve
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