• To remain on topic (RHCP): last weeks G0MJW, M0EYT and I were busy designing, modelling and building prototypes of alternative 2.4 - 10 GHz dual band feeds.

    There are several variations of the same theme, but I wanted to have a design without needing lathes or CNC-machines. The result is a (well known) 'cropped' patch, sized and matched with a waveguide in the center.

    It took some time to model the correct position of the feedpoint as the waveguide seems to introduce some 'issues', making it not trivial to find the proper position to have (what I call) the 'S11-balloon' circling around Z=1 in the Smith Chart.

    Attached a picture of sweeping my interpretation of a prototype, which we name ' 29-16° '. Return Loss (RL) could be improved even more with some tweaking of the patch height at the feedpoint position.

  • Hmmm... I bought a rocket LNB a while ago, advertised as 'PLL' but with a DRO after I opened it. However, the words 'Quartz Crystal Controlled' (or similar) were not in the casing.

    So, your situation is more misleading. I would address the seller/company and at least demand a refund.

  • With all LNB types (especially the unspecified ones) it appears to be customary to change the electronics while still selling them under the same brand name and type number.

    So when person #1 buys and determines to be a PLL LNB with 25 MHz reference, person #2 may find a DRO based LNB and person #3 may find a PLL LNB with 27 MHz reference.

    All with (about) the same external appearance and sold under the same name.

    I would think the trend is towards PLL type, and it seems also towards 25 MHz reference. So whenever you buy an LNB try to get new stock by ordering from a company with high turnover or close to the source.

    Especially when searching all the internet for an LNB no longer produced or hard to get, you probably have increased risk of getting an early type that is not usable.

  • pe1chl, I understand that, and you're right. But, the housing with PLL and quartz stabilized stickers to label and then obstruct other hardware is already brazen ....

    I will act as Remco recommends...

    @YL3ACK, I still work with a single PLL LNB from GOLDEN Media (GM-201), removed Quarz, drilled hole for coax with GPS sync clock. Works perfect.

    The only problem is the weather resistance and waterproofing, certainly not long-term stable... :-)

  • By the way, the PLL from GOLDEN Media locks in stable over a very large area. Better than the RCA's in the OCTAGON's. I went so far up the GPS stabilized PLL frequency (26.335 MHz) so I could still receive the 10706 MHz beacon at 435 MHz. The S / N was not worse. The same way in the other direction to convert the 10.5 GHz transponder to 1286 MHz.

    The best PLL I've ever had in my hand. :-)

  • Hello all,

    because a OM has asked me about the construction details of my helical dish feed i packed some detail photos into a Zip archive.

    Maybe someone here finds it useful for a diy helical dish feed.

    In the also enclosed PDF the calculations for the dimensions are described. Document fm W1GHZ.

    vy73 DB8TF

  • There are many ways to get the right dimensions.

    Helical feeds are really forgiving about small changes in dimensions.

    I found the hardest part of the assembly to get a good SWR, but after some fiddling with the small metal plate near the N-connector i get a good match.

    How this feed will perform in practise we'll see when we are allowed to TX to EH2.

    vy73 DB8TF

  • I continue to use my old AO-40 equipment. At this time, it worked very well for 13cm RX, as well in TX during contests. For my 1,2m full parabolic dish I have ony 2.5 turns to illuminate the reflector accordingly... May be that the circluar radiation is not ideal and something squint at 2.5 turns, but on the RX side I had the best results at that time ...

  • Good Morning all, I've just joined the Forum and thought I'd post a link to my Backfire Helix feed for Es'hail > Es'hail Backfire Feed

    The Backfire helix has received very little attention, yet it is well suited for use on prime focus dishes with 0.3 to 0.4 f/D's giving excellent illumination efficiency , low blockage and simple construction . Unlike the more common forward fire helix, they function without a reflector and naturally give a wide illumination cone with a sharp cutoff.

    73's ....Graham G8HAJ

  • G8HAJ : interesting! I read your blog post, and you were not sure whether you made a RHCP or LHCP feed. But I saw you also have a 23cm RX station.

    If I remember correctly for EME uplink is RHCP, so the reflections are LHCP.
    Assuming your 23cm RX-station works it must be able to conclude whether you made the right polarisation for 13cm?