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university:tools:pluto:hacking:listening_to_yourself [11 Jul 2019 01:41] – [Conclusion] Robin Getzuniversity:tools:pluto:hacking:listening_to_yourself [05 Aug 2019 23:06] (current) – [Tx On, and not sending a signal] Robin Getz
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 ====== Self Reception on the ADALM-PLUTO ====== ====== Self Reception on the ADALM-PLUTO ======
  
-Everyone has sung to a song on the radio, and it sounds great, as long as the radio is loud enough to drown out your terrible voice (or is that just me?). This is a phenomena known as self reception - when the signal you want to receive is being over loaded by something else.+Everyone has sung to a song on the radio, and it sounds great, as long as the radio is loud enough to drown out your terrible voice (or is that just me?). This is a phenomenon known as self reception - when the signal you want to receive is being overloaded by something else.
  
-The ADALM-PLUTO can do this to if you are not careful. The device will have Tx LO Leakage, and the receiver will pick that up, and may swamp out the signal you desire to actually receive.+The ADALM-PLUTO can do this too if you are not careful. The device will have Tx LO Leakage, and the receiver will pick that up and may swamp out the signal you desire to actually receive.
  
 ===== Tx On, and sending a signal ===== ===== Tx On, and sending a signal =====
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 {{ :university:tools:pluto:hacking:tx_lo_dds.png?600 |}} {{ :university:tools:pluto:hacking:tx_lo_dds.png?600 |}}
  
-This shows the peak at the signal (at 2405 MHz, where we expect it), and a LO leakage at 2402 MHz. It's difficult to see what this really means in terms of signal power, so we can look at the actual gain is set to by the Automatic Gain Control (ACG), and the Receive Signal Strength Indicator (RSSI).+This shows the peak at the signal (at 2405 MHz, where we expect it), and a LO leakage at 2402 MHz. It's difficult to see what this really means in terms of signal power, so we can look at the actual gain is set to by the Automatic Gain Control (AGC), and the Receive Signal Strength Indicator (RSSI).
  
 {{ :university:tools:pluto:hacking:tx_lo_dds_rx1.png?200 |}} {{ :university:tools:pluto:hacking:tx_lo_dds_rx1.png?200 |}}
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 {{ :university:tools:pluto:hacking:tx_lo_leakage_rx1.png?200 |}} {{ :university:tools:pluto:hacking:tx_lo_leakage_rx1.png?200 |}}
  
-Now our RSSI has gone to 90.5 dB and the hardware gain is set to 68 dB (which is still not at the max gain of the device), we are listening to ourselves, not the actual RF.+Now our RSSI has gone to 90.5 dB and the hardware gain is set to 68 dB (which is still not at the max gain of the device), we are listening to our own LO leakage, not the actual RF signal.
  
 ===== Tx Off ===== ===== Tx Off =====
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 dev 'ad9361-phy', channel 'altvoltage1' (output), id 'TX_LO', attr 'powerdown', value '1' dev 'ad9361-phy', channel 'altvoltage1' (output), id 'TX_LO', attr 'powerdown', value '1'
 </xterm> </xterm>
 +
 +This is the equivalent C source of:
 +<code>
 +    /* Create IIO Context */
 +    ctx = iio_create_context_from_uri("usb:1.3.5");
 +
 +    /* Find IIO device in current context */
 +    dev = iio_context_find_device(ctx, "ad9361-phy");
 +
 +    /* Find the IIO output channel in the current device */
 +    ch = iio_device_find_channel(dev, "TX_LO", true);
 +
 +     /* Write a one into the IIO channel attribute */
 +    ret = iio_channel_attr_write_longlong(dev, "powerdown", 1);
 +</code>
  
 Then we get: Then we get:
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 {{ :university:tools:pluto:hacking:tx_lo_off.png?500 |}} {{ :university:tools:pluto:hacking:tx_lo_off.png?500 |}}
 {{ :university:tools:pluto:hacking:tx_lo_off_rx1.png?200 |}} {{ :university:tools:pluto:hacking:tx_lo_off_rx1.png?200 |}}
 +
 +===== Tx On, but offset more than your channel =====
 +
 +If we shift things around a bit - if we configure things for an LTE10 signal, (LTE10 filter, with an LTE10 signal going out the DAC at full scale), and set the Tx and Rx to the same (2400 MHz), we can see this:
 +
 +{{ :university:tools:pluto:hacking:tx_lo_lte10.png?500 |}}
 +{{ :university:tools:pluto:hacking:tx_lo_lte10_rx1.png?200 |}}
 +
 +By offsetting things in 10 MHz steps, how far do things need to be away, so that it stops affecting the receiver:
 +
 +^ offset   ^ 0 MHz    ^ 10 MHz   ^ 20 MHz    ^ 30 MHz    ^ 40 MHz    ^ 50 MHz    ^ 60 MHz   ^
 +| RSSI     | 48.50 dB | 86.75 dB | 105.00 dB | 112.75 dB | 116.75 dB | 117.00 dB | 117.5 dB |
 +| ACG Gain | 25 dB    | 32 dB    | 59 dB     | 62 dB     | 67 dB     | 69 dB     | 71 dB    |
 +
 +This doesn't mean that you can't transmit/receive on adjacent channels, it just means that the receiver noise floor will not be higher and therefore the receiver will not appear as sensitive when you are doing this.
  
 ===== Conclusion ===== ===== Conclusion =====
university/tools/pluto/hacking/listening_to_yourself.1562802069.txt.gz · Last modified: 11 Jul 2019 01:41 by Robin Getz

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