Radio, railways, stuff...

Got myself a Heil headset for the laptop as the built-in mic picked up room noise. So, I figured it was time to try a QSO on QO100 even with the floating (frequency wise) Pluto. And - success! I had a short QSO with a German station. Just waiting for some small signal diodes to arrive before I glue the GPSDO output to the Pluto. There is a modification that involves removing the 40MHz TCXO and connecting an external source but the Leo Bodnar GPSDO output is 3.3V, too much for the chip in the Pluto. The mod involves two diodes in antiparallel to earth, plus a capacitor between the Pluto chip and the diodes, and another between the diodes and GPSDO. Hopefully that will work and the surgery on the Pluto does not consign it to the scrap pile! The GPSDO I have has two outputs, one 25MHz to the LNB, and one 40MHz for the Pluto. I still need to sort the dish as signal strengths are still below where I expected. I am also concerned at the filter/pre-amp because it does not draw as much current as it is supposed to - it works but I wonder if there is enough drive. It may be perfectly ok but the next step has to be locking the Pluto so it doesn't wander all over the place.

Overcast today so I made time to try to align the dish a little better. One long Ethernet cable got the laptop under the dish and with SDR Console looking at the beacon I did manage to peak it a bit but I think I can do better yet. Oddly, no amount of moving the POTY in or out or skewing it made any noticeable difference. I did note however that the rain cover I made only makes a tiny bit of difference. The sky is a little overcast today so maybe signals are down because of the cloud cover. Anyway, I made a test CQ call and could hear my voice coming via the WebSDR nicely, so I made a couple of CQ calls but got no reply. I think I chased everyone away because after this there was very little activity. So, at least I know I am getting out and so a success at least in part. One thing though, the tuning is going to take some getting used to yet. The basic frequency conversion between the 10GHz band, the 2.4GHz transmit and 739MHz receive is 10GHz - 9750 = 739MHz rx frequency, and 10GHz - 8089.5 = 2.4GHz tx frequency. With my setup the receive frequency needed for SDR Console to get the same audio tone as found via the WebSDR is 6.8kHz higher but the transmit frequency is 21.8kHz higher. These offsets are repeatable in that if I chose a signal on the WebSDR I can reliably find it via the Pluto if I use the offset. So, maybe a bit more dish alignment but also I do still need to sort out the frequency lock for the Pluto.

(updated) I finally had all the bits in one place to sort out the power supplies for my QO100 box. I managed to assemble the 'filtered S-band driver/amp' and the 'QO100 5W amp' kits from AMSAT UK and learned a lot about SMDs like (a) I don't like them (!) and (b) I find it far easier, being short sighted to just look up close than use magnifiers. Anyway, the kits both went together as planned and passed the basic test relating to current draw so I was hopeful that I had actually not managed to mess them up. I also had much fun assembling the LMR600 coax with memories of central heating installation! Finally, with a 12V PSU, a 12V to 5V module and as 12V to 24V module from eBay and tie wraps to hold stuff in place I managed to get volts where needed and gingerly turned it all on. The Pluto found the Ethernet, the GPSDO lit up and SDR Console found QO100. Nothing odd in that because it was all working before but is now assembled into a box. On the left (the door) are the two voltage converters and the GPSDO, and on the right the Pluto (LHS), the bias tee (central) and the 2.4Ghz amp (RHS) with the driver/amp above. The most awkward bit is the USB to Ethernet adapter. The LNB input, 25MHz output and the GPSDO input cables enter from underneath and go out to the dish via the white conduit, and the LMR600 enters through the side into a short piece of LMR195. There is a 12V PSU mounted on the outside of the door in a separate box. But does the transmit side work? That's all new. With a Windows laptop running SDR Console and the MacBook looking at the WebSDR both sitting on the freezer in the garage (so I could see if the QO100 box caught fire!!) I managed two very short test transmissions. It works! The audio was a bit naff but that is probably down to me not yet familiarising myself with SDR Console and using the mic in the laptop. So, after ages and ages of getting bits together and everything else getting in the way it's almost done. Signals are still down compared to other, more successful setups out there but at least now it seems all I need do is properly align the dish and sort the audio side out. And tidy the wiring. Oh yes, and sort out the GPSDO locking for the Pluto.