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university:tools:pluto:users:non_quad [26 Jul 2019 17:14]
Robin Getz [UHD]
university:tools:pluto:users:non_quad [01 Feb 2021 14:47] (current)
Iulia Moldovan
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 Receiving is where things can be more complicated. Most (all) integrated transceivers include some sort of Quadrature tracking corrections which try to ensure the signals are correct, and any imperfections in the chip or external circuitry (balun, non-differential traces, etc) are removed. Receiving is where things can be more complicated. Most (all) integrated transceivers include some sort of Quadrature tracking corrections which try to ensure the signals are correct, and any imperfections in the chip or external circuitry (balun, non-differential traces, etc) are removed.
  
-While the frequency domain plot does look close to the same, but we can see that the amplitude is jumping up and down by a few dB(which is impossible to show in a static picture like this).+While the frequency domain plot looks the same, we can see that the amplitude is jumping up and down by a few dB (which is impossible to show in a static picture like this).
  
 ^  Analog Loopback, Frequency Domain, ACG On, Quadrature tracking On  ^  ^  Analog Loopback, Frequency Domain, ACG On, Quadrature tracking On  ^ 
 | {{:​university:​tools:​pluto:​users:​rf_lo_same.png?​700|}} | | {{:​university:​tools:​pluto:​users:​rf_lo_same.png?​700|}} |
  
-Its easier to look at this in the time domain. Here the amplitude difference between I & Q is random based on the random difference between the phase of the Rx and Tx PLL. This is indeed completely random and will change any time either PLL settings are touched. Moving one LO to a different setting, and back again, will change this phase offset (which manifest itself as a magnitude difference between I and Q).+It'​s ​easier to look at this in the time domain. Here the amplitude difference between I & Q is random based on the random difference between the phase of the Rx and Tx PLL. This is indeed completely random and will change any time either PLL settings are touched. Moving one LO to a different setting, and back again, will change this phase offset (which manifest itself as a magnitude difference between I and Q).
  
 ^  Analog Loopback, Time Domain, I & Q Data, ACG On, Quadrature tracking On   ​^ ​ ^  Analog Loopback, Time Domain, I & Q Data, ACG On, Quadrature tracking On   ​^ ​
 | {{:​university:​tools:​pluto:​users:​lo_same_time.png?​700|}} | | {{:​university:​tools:​pluto:​users:​lo_same_time.png?​700|}} |
  
-You can change this magnitude difference digitally by post-processing the sampled data, by using the Phase Rotation control in IIO oscilloscope. It doesn'​t change the phase relationship between I and Q, but does change the effective sample time relative to the PLL, and therefore changes their relative magnitude. By changing this, you can effectively make either of the I or Q zero, and only receive the signal the other (Q or I), indicating that the received signal is "​real"​ (all information can be received just on one signal channel, and it has no phase or quadrature information.+You can change this magnitude difference digitally by post-processing the sampled data, by using the Phase Rotation control in IIO oscilloscope. It doesn'​t change the phase relationship between I and Q, but it does change the effective sample time relative to the PLL, and therefore changes their relative magnitude. By changing this, you can effectively make either of the I or Q zero, and only receive the signal the other (Q or I), indicating that the received signal is "​real"​ (all information can be received just on one signal channel, and it has no phase or quadrature information.
  
 ^  Analog Loopback, Time Domain, I & Q Data  ^  ^  Analog Loopback, Time Domain, I & Q Data  ^ 
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 ===== SDRangel ===== ===== SDRangel =====
  
-SDRAngel also can turn on/off Quadrature tracking with it's Hardware control buttons.+[[https://​github.com/​f4exb/​sdrangel|SDRAngel]] also can turn on/off Quadrature tracking with it's Hardware control buttons.
  
 {{:​university:​tools:​pluto:​users:​sdrangel_controls.png?​direct|}} {{:​university:​tools:​pluto:​users:​sdrangel_controls.png?​direct|}}
university/tools/pluto/users/non_quad.1564154095.txt.gz · Last modified: 26 Jul 2019 17:14 by Robin Getz