Dielektrische Linse für POTY und BaMaTech Feed

    I order a Venton EXL Twin for the mod of Bamatech.



    Take of the lense, was not a problem. Try to fit it to the Bamatech Duo Fed but it don´t fit



    Measured the inner diameter of the Bamatech with 18 m/m


    Measured the inner diameter of the Venton with 18,7 m/m



    Looks good but don´t fit together. Test of Bamatech with this lense not possible.



    73 Joachim

    I would use the "poor man's lathe", a simple needle file and go round and round to get the 0,35mm off.

    Needs a bit of care and time, but will work...

    Quote from G0MJW




    Please compare with rocket and post-results

    HERE IT IS!

    Same POTY feed, same LNB (GM201new), different lenses: Venton EXL-T vs. PE1CKK Polyamid lens.

    The Venton EXL-T lens gives a 3dB better S/N at my dish (Kathrein CAS80 f/D about 0.66).


    73, Thorsten

    Quote from DL9SEC

    Same POTY feed, same LNB (GM201new), different lenses: Venton EXL-T vs. PE1CKK Polyamid lens.

    The Venton EXL-T lens gives a 3dB better S/N at my dish (Kathrein CAS80 f/D about 0.66).

    Tnx for report,

    Did you adjust or correct the focus point between the two lenses?

    And when yes, what was the difference in mm?


    73´s de Robert, DD4YR

    Quote from DD4YR

    Tnx for report,

    Did you adjust or correct the focus point between the two lenses?

    And when yes, what was the difference in mm?


    73´s de Robert, DD4YR

    Unfortunately no. No possibility to go further backwards, the reflector hits the mount.

    So in both cases I would say, that i am a bit out of focus towards the dish...

    Quote from DL9SEC

    Does anyone know, where the focus point of the Venton lens ist?

    As far as i remember, the PE1CKK lens has it about 11mm towards the dish...


    Ich denke, es ist ungefähr in der Mitte, aber wenn man es flach auf das POTY-Pflaster legt und das Objektiv in der gleichen Position, in der es sich mit dem Ventron-LNB befunden hätte, sollte es ungefähr richtig sein. Dies erfordert normalerweise einige geringfügige Änderungen am Vorschubarm - das ist nichts, wovor Sie sich fürchten müssen, sehr einfache Metallarbeiten. In einigen früheren Beiträgen finden Sie Anregungen zur Unterstützung


    I think it is about in the middle but if you have it flat to the POTY patch and the lens in the same position it would have been with the Ventron LNB is should be about right. This will usually require some minor modifications to the feed arm - that's nothing to be afraid of doing, very simple metalwork. See some earlier posts for ideas for support - plumbing.



    G0MJW


    Thanks for the reply. I am aware of all of this.


    As you can see on the first photo, the optimum focus sits at the Astra feed waveguide. Unfortunately the focus of the POTY lens sits about 20mm out of that "focus plane".

    As you can see on the second photo, the POTY reflector hits my mount clamp. At the most I could gain about 5mm if I use another mount. I don't know, if it's worth the trouble (have already about 39dB S/N at the NB beacon and meanwhile a perfect decode of the WB beacon).


    As far as i see, the focal point of the PE1CKK lens is closer to the optimum than that of the EXL-T lens in my setup, but the Venton lens gives a better result though.


    I think to have a real and general comparison of the lenses, a setup should be used where the focus can be reached and tweaked for both lenses (agree with DD4YR and PA3FYM). I don't have this setup here...


    73, Thorsten

    This is what I mean by doing some simple metalwork to adapt the mount so that the reflector does not hit the clamp. Recently I had the same issue all I needed to do was make a small adaptor plate and adjust the feed arm to be slightly lower. It's the sort of metalwork that can be done with a drill and files.


    In your case, it looks like you just need to raise the height of the POTY and then bend down the feed arm to get it back in the correct place vertically.




    Above is what I did last week for a lash up system using a free 1m dish. A small aluminium plate rests on the original LNB feed holder (bottom half) and is held down with the original screws. The new LNB holder (plumbing supplies) is mounted further back so now the lens is the correct position relative to the focus and the feed is higher so it clears the feedarm. To compensate this the arm is angled slightly lower - it bolts to the back bracket with 4 bolts and this allows easy adjustment by slotting the bolt holes.


    In practice I don't think the small vertical error if you do not adjust the feed arm angle will be all that significant for a 0.7 f/D dish. It's much more critical with short focal length dishes but with an offset you can simply adjust the elevation to compensate for this., within reason. The use of several LNBs mounted horizontally to receive multiple satellite slots is an example and seems to work fairly well over a few degrees.


    Mike

    Hmmm. Really good hint. My mounting plate has a tilt of 11°, so if I put it back to 0° I can raise the POTY a few cm with the same result, but in this case I should be able to adjust the focus for optimum.


    Will keep you in the loop... :D