Pluto Mods: just 1 part PTT, DC-Mod, GPSDO Mod, Ethernet connect

  • Here are the ADALM-Pluto mods according to the latest knowledge, with ext. Ref. In (25 / 40MHz), PTT-Out and GND-Mod. so that Pluto doesn't crash anymore if you power any device nearby.

    The PTT output only requires an LTV-354T optocoupler which is soldered directly to the two pins GPO0 and GPO1 without a series resistor, no further transistors are required, but the switch-off functionality is still achieved when the Pluto is booting.

    To switch GPO-Pins for PTT the Pluto DATV Beta Image from 05.02.2020 from F5OEO is required (also for narrowband SSB operation).

    The heat sink set comes from the Raspberry PI 4.

    A GPSDO (e.g. Leo Bodnar) or a TCXO or OCXO can be connected to the external reference input.

    You can find out how to reprogram the frequency from 40MHZ to 25MHz on my page.

    At 25Mhz the LNB can be synchronized with the same GPSDO as the Pluto, so the beacon stabilization of the SDR console is obsolete.

    The 2dBm (1.6mW) from the Pluto device can be easily increased by 33dB with the PA according to DB4UM, so you can drive a 20W SG-Lab PA with 500mW from this small unit.

    I've used the DB4UM (driver) amp directly for test purposes with about 3.5W output after 10m low-loss cable on a 65mm dish with POTY dual patch feed. The amp connected between Pluto and POTY is able to generate a readable SSB signal on the satellite with around 70% of the beacon level.

    To connect your Pluto by ethernet the ideal adapter is the ICY BOX IB-AC510 where no extra OTG adapter is needed. Just plug the micro USB plug to the left connector at the Pluto and supply 5V to right-hand USB connector. The settings are managed by updating the config.txt file on the PlutoSDR mass storage device.

    By default DHCP is activated, but you can assign a static ip at this tag:


    ipaddr_eth = # <-- assigned fixed ip

    netmask_eth =

    After this modification you have to eject the Pluto drive in Windows to activate the new configuration.

    73, Mike DK1ML

  • Hi Mike,

    The Pluto RF LO requires a 1.8V (max.) signal as far as I know. Probably too much input level could damage the chip. How did you manage this? Do you use an external level shifter or divider?

    73 Mike

  • Hi Mike,

    mostly the external level for the TX/RX chip is too low, which results in spurious emissions.

    You can put almost any rectangle (not sine!) signal via the on board 18pF capacitor C123 to the clock pin, this is attenuated enough. If you use a reference clock below 25 MHz it is strongly recommended to use a second 18pF capacitor in parallel.

    73, Mike

  • Hi Mike,

    I have troubles getting a stable Ethernet connection to the Pluto. USB works, but via Ethernet cable (both, attached to my home network as well as directly connected from a separate laptop to the Pluto's OTG adapter) it has interruptions in transmit (on all bandwidths).

    Is there a trick for that? I use an external 25MHz clock. And SDR console. I also increased the clock voltage without any success.

    I also tried several USB chargers for supply.

    73, Andreas