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Re: [Discuss-gnuradio] Capturing maximum complex value
From: |
Marcus D. Leech |
Subject: |
Re: [Discuss-gnuradio] Capturing maximum complex value |
Date: |
Sun, 17 Mar 2019 12:55:46 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
On 03/17/2019 11:09 AM, John Ackermann N8UR wrote:
I'm working on a flowgraph that generates an output waveform about 375
kHz wide with very high peak-to-average power -- at least 20 dB. This
is sent into a USRP1 with BasicTX board to generate an output at 29
MHz. I'd like to show in the flowgraph GUI the peak instantaneous
output level, to help in setting the gain.
It's painfully clear on a spectrum analyzer when the gain is too high.
The attached shows (a) single CW carrier at max output (orange); (b)
output without clipping (yellow); and (c) output with occasional
clipping (blue). These are max-hold plots so the clipping is caught
even though it happens only very infrequently.
Is there a probe or other function that can capture and hold the
maximum instantaneous value of a complex stream? If not, is there a
way to create that capability out of other blocks?
And, am I barking up the wrong tree -- is the distortion likely caused
by the complex output being driven into digital clipping when enough
vectors add up, or is this a function of the analog conversion in the
USRP? i.e., is the problem likely to be on the input or output side
of the DAC?
Thanks,
John
ANother approach is to simply multiply your signal by, let's say, 0.5
before being presented to the radio. Crank that value up until you get
distortion, then back off by sqrt(2).
Re: [Discuss-gnuradio] Capturing maximum complex value, Ron Economos, 2019/03/17