A couple of notes on my first QO100 QSO tonight

  • Hi,

    A couple of notes on my experiments resulting in my first QO100 QSO tonight. Not spectacular, but perhaps this story has one or two points that may help others getting their kit ready.

    I've started with the PE1CMO kit, which has been reported by others already to work very well, but I'll need to make the setup a little different since I plan to use this for Jamboree-On-The-AIR (JOTA) and the scouting hut is surrounded by trees blocking south, so the dish and transverter need to be at at distance - a distance big enough that a run of coax on 70cm is an issue. I also made a remote control box so I can see status from the scouting shack.

    Unfortunately, the dish I planned to use for initial tests could not be used since the disk mounting hardware was supplied incomplete by the sat shop - the shop will fix but not tonight. So, instead, I tried a 40cm "camping dish", that was sold by LIDL a few years back.

    Aiming the dish, small as it is, is an issue (it can't be pointed that accurately).

    To get a ballmark aim I connected a sat receiver, adjusted to BBC news (28.2 degrees, 10818, Vertical), so it uses the same LO and polarisation as needed for the NB transponder. Since the LNB supplied with the CMO kit is modified (5 volts instead of the usual 13/18 volts), I used a RF splitter and a DC blocker to the sat receiver so the sat receiver would not damage the 5V LNB. Given the wide angle of the small dish, when pointed to 28.2, pointing to 25.9 is not hard.

    The splitter had a surprise. I had bought a splitter with F connectors at a hardware shop, assuming it had the same arrangement as similar radio/TV splitters with belling-lee connectors, with a small transformer inside, but to my dismay the F-connector one has decoupling capacitors in the circuit so I cannot use it if I want to feed the LNB. The older belling-lee version was just a transformer though, so with some belling-lee->F adapters and the DC blocker in the path to the sat receiver, and the other port of the splitter to the CMO kit I could safely connect the 5volts-LNB Rene had supplied.

    (note that really cheap splitters actually are not splitters at all, they just have 75E resistors in there, but the metal belling-lee ones are actually pretty good certainly considering price. Use an ohm meter to verify!)

    Once I had TV signal, tuning to the beacons was relatively easy (note that the CMO kit uses GPS reference throughout, so there is little frequency uncertainty). Question: Would AMSAT-DL consider changing the lower beacon from SW to FSK? That would make aiming a lot easier still.

    I didn't want to modify the LNB that came with the CMO kit (it is a nice reference), and had ordered a few SR3602's before (very cheap at aliexpress). I had assembled a POTY antenna earlier, and had sawn-off and made-fit a SR3602 LNB for the POTY before, but wasn't sure the POTY antenna would work. So I connected another SR3602, unmodified, to try to see what it would do to my signals.

    There was a second surprise here: the SR3602 has two ports. The port in the back would make the SR3602 unstable (signals sounded like aurora), while the port in front was a lot more stable - it still drifted of course but at least the tone was constant. I tried this on two SR3602's and both had the same behavior, so be aware. (the "front connector" is closest to the horn, or where the horn was before it was sawn off).

    With the POTY antenna on the dish, I was able to receive on an unmodified SR3602 (albeit with drift and offset of course) so the POTY antenna did work as well. What was left was to connect the 2400MHz output of the CMO kit to the POTY, and then, even with just a 40cm dish, I could make carrier on the NB transponder.

    Once that worked I found an old friend on the band (hi Hendrik Jan!) called him, and the rest is history. I didn't even need to drive to full power and didn't need the 20W that the CMO kit can make was really too much even with the too-small antenna.

    I hope some of these comments are useful for others making their way to the band.

    73, Geert Jan