Posts by DH2VA

    The Pluto is rather power hungry so you have to be super certain about the PSU for the Pi4 (which itself requires a bit of power). Have you tried a USB power monitor dongle to measure the voltage? You can also use a separate USB line to power the Pluto via its second USB socket (from a 5V /1A charger, NOT from another Pi4 port).

    DD4YR is correct.. the any bad matching on the PA output will not (or only at a tiny degree) backpropagate on the PA input.. This is actually related to the S12 S-parameter and can be n the order of 20 dB. So even with a full short on the output, your input return loss is still -20dB and therefore close to perfect.

    I did have a high SWR issue in the past but the bag cured it, at least until today.

    That sound already very odd and should be the first thing to be checked. It could be a faulty cable.. if this is not 50 Ohms all the way (including connectors) it can transform even a perfect 50 Ohm match into anything else triggering the SWR warning of the PA.

    you should not look on the Es'hail-2 footprints on the WWW as they only list the spot beams for the TV programmes. The AMSAT payload (QO100) has dedicated global beams which are not listed in the usual places but here:

    https://amsat-dl.org/p4-a-nb-t…and-operating-guidelines/


    Be aware, that actually two transponders are used for hamradio: one for TV and one for narrowband (SSB, CW, digimodes), check out the amsat-dl.org website for more information (frequencies, polarisation). Don't bother looking for the TV programmes of the main satellite.

    Use SDR-Console with it's integrated RX offset/drift correction (locking onto the beacons). This should take care of the LNB drift (if it is a PLL LNB) and the RX drift of the Pluto. When transmitting, your signal will eventually start drifting which is the remaining unless you start modifying the Pluto's reference frequency.

    dbFS is decibel relative to the full scale of the SDR receiver (which is max sum amplitudes of all signals to the SDR input). It is rather pointless to give any numbers here as these will vary depending on LNB, cable used, temperature to only name a few.


    The ONLY way to properly max the antenna pointing is to max on any of the beacon signal levels, regardless of the reading itself. Then to compare different setups to each other you have to check the transponder excess noise referenced to the thermal noise outside of the transponder BW. Select a display BW of at least 3 MHz and you should see a hump about 600 kHz wide and 3-4 dB sticking out of the noise floor left and right. This is the transponder passband and the 'stick out' value is the only one which is independent of the SDR software used. For 80cm, 3-4dB is fine, if you don't see this I would not touch the TX and figure out RX first.

    I don't think the OMs with an errornous setting of 3.0 kHz in the TX modulation filter (SDR console for example) are the problem of this topic but rather the few gentlemen overdriving their PA and therefore generating up to 10 kHz wide splatter (which is actually IM3). Many operators have good to excellent signals, some of the overdrivers are reasonable once you explain the cause of their bad signal to them (actually, the readability of the voice does suffer considerably as well). The very small fraction of those who don't care, I have no idea what to do.

    Thanks to DL5QY sending me his dead PLUTO, I was able to trace down the problem and offer an explanation for the probable cause.

    TLDR: GND potential difference between SMA and USB frying L7 which then shorts the internal 5V line.
    A more detailed diagnosis is attached in the zipped PDF.

    It depends. If they actually require high speed S-band downlink then 4m might be necessary due to their link budget.
    HOWEVER: the required pointing and tracking accuracy coupled with the high angular rates for a LEO satellite will make this super complicated and carries a huge risks for problems and/or failures.

    Bottom line:

    if you don't need 4m, than I completely agree with HB9SKA

    if you do need 4m because of link budget, you have designed your mission wrong.