Posts by DM5RM


    Ja, der Windungssinn stimmt. Ein durchgehendes PVC-Rohr als Träger und noch ein zweites als Witterungsschutz sind aber wahrscheinlich problematisch, wie dl6dca schon bemerkt hat. Zum einen durch den kapazitiven Einfluß (erhebliche Verstimmung), besonders aber durch den vergleichsweise großen Verlustwinkel von PVC gegenüber Luft oder Teflon.

    73 Roland

    I looked at adding 1, 2, 3 director elements to the POTY antenna to better suit longer F/D dishes, but it only gained a dB or so before I exceeded the limits of the student CST. Anything more complex was well beyond the capacity of student CST though


    If you have some experience with Matlab/Octave, you might give openEMS a try.…Simple_Patch_Antenna.html

    This is an open source 3D-FDTD simulator, available for 64Bit Windows and Linux.

    The size and complexity of the models is only limited by the computer's RAM and the computing time. Compared to e.g. HFSS I could not find any significant differences in the results.

    By the way, a Python interface is in preparation.

    73+55 Roland

    A kind of USB extension can be realized with two USB-to-LAN adapters for the Pluto. This is then a simple peer-2-peer network with two fixed IP addresses.

    The advantage is that you always have full bandwidth, even if other family members stream UHD videos through the router ;-)

    On the PC side I use an "ASIX AX88179 USB 3.0 to Gigabit Ethernet Adapter". However, this type does not work reliably on my Pluto-USB-OTG, although it is classified as compatible by AD. But an "ASIX AX88772 USB2.0 to Fast Ethernet Adapter" does it without problems on the Pluto side.

    This evening I did also some reflection measurements, but using a -30dB directional coupler.

    Low cost (but good) directional coupler

    The setup was simple: The Pluto-Tx was connected to the (reversed) dico input via an attenuator (-10dB) and the Pluto-Rx was connected directly to the -30dB output to measure the reflected power. So the corresponding SATSAGEN settings for "level correction" were -10dB for Tx and -30dB for Rx. A calibration was then performed, with the dico main output being short-circuited. The first screenshot shows the behaviour of a quite good 50 Ohm termination resistor at the dico output.

    After that this procedure was repeated, but for calibration the output was simply left unconnected (open).

    Finally I connected a 14 dBi wifi flat panel antenna.

    Dear all,

    I have just found the program SATSAGEN by Alberto IU1KVL on the web.

    It turns a Pluto into a very useful measuring device. A generator and a spectrum analyzer were realized, whereby the entire frequency range of the Pluto is supported.

    In the "Spectrum Analyzer w/Tracking" mode, for example, filter passband curves can be determined very easily. As a very first test I measured a 2.4GHz filter, see screenshot. For tuning and matching of antennas, only a suitable directional coupler would be required in addition.

    At Albertos blog you find the download page and also a video with helpful explanations:

    Thanks to Alberto, who provides SATSAGEN to the HAM Radio community free of charge.

    73 de Roland


    Hi, Robert,

    you are right, the term "xo_correction" is a bit misleading.

    You just have to enter the true clock frequency in Hz. For example:


    xo_correction = 40000123

    But if this value differs from the nominal clock frequency (e.g. 40.0 MHz) by more than 200 ppm, the Pluto will ignore it.

    Instead of editing the config.txt directly, you can also type in

    fw_setenv xo_correction 40000123

    pluto_reboot reset

    via console. In any case, the correction is not applied until a reboot.



    Like the LNB, the Pluto can also be operated with an external 25-MHz clock.

    It is not necessary to recompile the firmware.

    The applied clock frequency must simply be transferred to the Pluto with the following commands:

    fw_setenv ad936x_ext_refclk "<25000000>"

    fw_setenv xo_correction 25000000

    pluto_reboot reset

    This is worth a try.


    Looks very good. :)

    By the way, the directional coupler at the output can be omitted and thus may bring a few tenths of dB more output power to the antenna. The amplifier already has a coupler built in and you can simply connect the power meter to the second MMBX socket. The corresponding calibration value has to be determined of course, but this would be necessary for the external coupler as well.

    But one could also realize a deluxe version and use the external coupler to measure additionally the reflected power.


    Hi Piero,

    the main reason for the input transformer is to avoid a ground loop, which can cause problems such as increased phase noise and spurious signals. Besides, one gains a degree of freedom for the adjustment to the output level of the used external OCXO or GPSDO.

    If the switching threshold of SN74LVC1G125 is assumed to be 0.9V and its input protection diode conducts from 0.5V, you get about 2*(0.5+0.9)=2.8Vpp as optimal input voltage for the chip. This applies at least for sinusoidal driving to achieve about 50% duty cycle at the output. A different transformation ratio obviously requires a correspondingly adjusted value for R1. Placing R1 on the secondary winding of the (non-ideal) transformer reduces overshoot when the input signal is square wave.

    The transformer is certainly not the cause of the 10 MHZ problem. In the ADI forums it is reported that at this frequency a sine wave with 1Vpp at the AD936x clock input is mandatory. The SN74LVC1G125 simply cannot do this.

    But for us 25MHz are much more interesting anyway, because they are also needed for the LNB.

    vy 73,


    Now the practical part.

    For the test the circuit was simply soldered together, quick and dirty, without a printed circuit board.

    U1 and the Pluto-XO are almost pin-compatible. However, the metal housing of Y3 prevents a simple piggyback mounting.

    The transistor Q1 is placed upside down, with the emitter at C121. R1 consists of five parallel-connected 1k resistors, because they were just available.

    A level of about 6.5dBm is just enough to switch to external clock at the given impedance ratio of the input transformer. At more than 12 dBm, however, U1 is increasingly overdriven.

    With this circuit the Pluto was able to operate with external clock frequencies between 20 and 50 MHz. 10 MHz unfortunately did not work.

    The currently applied clock frequency (in the example 25 MHz) must be submitted to the Pluto with the following well known commands:

    fw_setenv ad936x_ext_refclk "<25000000>"

    fw_setenv xo_correction 25000000

    pluto_reboot reset

    IK1IYU recently mentioned, that it


    "Looks like the easiest pluto sdr tcxo removal….is NOT removing it at all. According to Analog Device Pluto schematics, pin 1 of the tcxo is an Enable/Disable pin and simply grounding it should disable it."

    TCXO for Pluto

    But if pin 1 is not connected statically to GND, an automatic clock selection can be realized with little effort.

    This is made possible by TI's SN74LVC1G125 chip, which has a low-active enable input and accepts input signals up to 5V with 1.8V VCC. So a single Si-npn transistor provides automatic source switching, a pull-up resistor is not necessary.

    The tested circuit diagram is attached.

    The advantages are:

    The original XO does not have to be removed.

    The Pluto still works even if no external clock is fed in.

    And last but not least, accidentally too high Clk levels or ESD no longer directly endanger the heart of Pluto.