DL1GNM going to be QRV soon

1st Official Post

    Hello, setting up my QO-100 station. I've an unused 120cm offset dish that was installed in the early 90 for TV. I watched BBC on 28.2°E using this dish at last. And it has a polar mount but this is not moveably anymore (rust ...). It was quite easy to find the position by moving only 2 degrees west. BADR-4 on 12523 MHz H was found and helped me to align the dish to the required position.


    I'm currently using the unmodified and a bit wobbling HD-BP2 LNB, POTY feed, RTL stick with SDR console and "autotune".


    Noise floor is at -90dBm, the CW beacon around -58dBm. Temporarily mounted, see pictures...


    Comments please. And more to follow soon.


    73 Mike

    Achim, I did. But the measurement tools that are included are too inaccurate (or I've not found the right one). Really not big changes. It's now at almost the same position as the old feed was.


    Dish size:

    Height: 129cm

    Width: 120cm

    Depth: 11cm

    Distance: 91.5cm (middle of dish to patch)


    F/D something around 0.68


    I'll try another dielectric lens as soon I get one.


    Did you expect more S/N?

    • Official Post

    I expected to be the patch feed further out (literally flush to the holder).. seems too close to the dish to me. 1-2 dB are easily lost there. With a 1.2m dish you might be forced to check on absolute signal level rather than S/N as you will see transponder noise and the S/N will max out. Or you optimize on the increase of transponder noise relative to the non-transponder noise at (as example) 1 MHz lower.

    Might be non-critical on NB signals but for WB every dB counts.

    The picture of SDR console does not show the real true peak or value. That's the reason why I did the signal monitoring on the CW beacon. It's > 30dB S/N. Did not the same with the PSK beacon yet...

    ... to be done soon!

    Meanwhile most of my rig is ready. I'm able to receive the DATV beacon

    A71A with an C/N MER ~ 7.1 dB.

    PE1ASH (1000kS on 10494750) C/N MER - 5.4 dB today.

    The dish is almost the same that BATC uses now, see:

    https://wiki.batc.org.uk/Es%27hail-2_Ground_Station


    The transverter is missing and will be mounted in the outdoor box when delivered. And the LNB has to be modified to get rid of the wobbling. And of course less frequency drift.


    CU soon. 73 Mike.


    Just an update. I'm QRV, DD0KP borrowed me a transverter while I'm waiting for my own one. Made one QSO with 100mW in SSB, my signal was 14dB S/N peak. With the 2 W amp I'm reaching beacon level. Transmitting works now after correcting a mistake I made with the patch ^^.


    The other optimisation was moving the radom closer to the lens. See picture. Now it must be very close to the optimum feed point. The distance from the lens is only a few mm to the cap,


    The Venton LNB has an excellent dieletric lens but is too far away form the best feed point. See results below.


    Here the patch now correct and closer to the cap (removed for the photo):


    Some results with the A71A DATV beacon (HD-BP2 LNB still unmodified):

    Venton Rocket Lens LNB seen as in picture: MER 5.2dB D2

    POTY with POTY lens but without radom: MER 6.9dB D4

    POTY with Venton Rocket Lens, but without radom: MER 8.8-9.0dB D6

    POTY with Venton Rocket Lens, radom old position: MER 7.7dB D5

    POTY with Venton Rocket Lens, radom new position: MER 8.7-8.9 dB D5/6


    I think that's OK. My old Hirschmann dish got back into life (it was installed there more than 25 years ago).

    73 Mike

    Claudio,

    it's a EXL-S. Got one from Heiner and bought a few more. This performs well if it is in the focal point of your dish.

    I took off the lens and Heiner is right: I see the difference. Because I want to modify the HD-BP2 - feeding 27 MHz form my shack - I stay with this one. And I can use is for DATV at the same time using the second output.


    73 Mike

    I wonder if the circular waveguide (22mm Cu tube behind the mount) could be shortened without any performance issues? Shorter tube would make the total feed assemply look a bit more compact....(more for optical reasons than anything else, hi hi)


    It is randomly extended anyway by the various connected LNB types, so I guess that total length is perhaps therefore not overly critical?


    73, Oscar DJ0MY

    Hello David, i did it another way, but i've cut the horn where it has +- the diameter of the inner size from the copper tube, i think 4mm is left from the lnb, just enough to punch it into the pipe. Then i used an adapter with inner dia 22mm,outer 25mm which sleeves over the copper tube and the waveguide from my feed.NOTHING is screwed and fits nicely,doesn't move anything.

    73's Jerry