Posts by DH2VA

    Obviously, the 2.4 GHz itself cannot enter the LNB due to waveguide cutoff. 4x2.4 GHz = 9.6 GHz, which is a theoretical possibility.

    But assuming you stick to the legal power limit on 13cm and drive the final amplifier not too recklessly, the harmonics should be far below any danger limits for the LNB. You want to use a 4 W amplifier presumably for SSB so you would need to back off a bit anyways. And then, I don't think harmonics are a problem.


    Have fun!

    David G0MRF will there be a technical analysis of the mishaps? I have tons of questions but for these to be answered a more detailed breakdown of the sequence of events and the lessons learned would be helpful.

    Thanks for supporting this education project, as always!

    The case of Arecibo is a sad but classic case of negligence and budget cuts. The hurricanes did not killed it, they just gave it the final blow. Working with them in 2014 for the ISEE-3 recovery, they were already struggling then for basic maintenance.

    oh2uds it seems you have a severe ground loop problem and as USB is not galvanically isolated, this will lead to future defects unless fixed. You have to break the loop somewhere, either by inserting a capacitor in the SMA GND input or using an OTG USB-Ethernet adapter (Ethernet is galvanically isolated).

    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.