Posts by dh5nn

    I repeated the measurements with a short 20cm pigtail from the patch to the miniVNA Tiny and according recalibration. This is what i get now:

    This looks much more consistent with what I would have expected. Thanks for the hint DL9SEC. Those larger loops are not observed anymore (although they were to be expected as I've learned here) and the measurements are less noisy. I simply wasn't aware of the impact of the cable length. I put markers 1 and 2 where I would suspect the double dips to be located and marker three around 1.4GHz.

    G0MJW Indeed, the real test is what counts. Unfortunately my PA is not ready yet, so I can happily induldge in more or less meaningful measurements.

    To me everything looks okay-ish so far and I think I can leave my patch as it is and start doing some careful tests on the air as soon as my PA is finished.

    Just for my own understanding: taking the simplified two antenna model into account and assuming that in my measurement above marker 1 corresponds to the inductive and marker 2 to the capacitive antenna: their difference in phase, should be 90° in the optimal case. Is this correct?

    Thanks to everyone so far already

    PA3FYM Oh, you mean an even smaller balloon? I haven't even considered that. My guess is that it would be below the measurement noise then, but I'll have a look tomorrow.

    By the way: I am actually not too worried about the loss in general, that's why i wrote that everything looks fine per se, except for the very spirals which puzzle me. Nevertheless, as you wrote earlier in this thread: test equipment is cheaper and thus more available than ever and people may get lost in some unfocused over-optimization (I'm paraphrasing here) and I certainly agree. But I also see this as an opportunity to overcome some "street knowledge" that is traded like folklore.

    DL9SEC Ah, you're right. Of course I calibrated directly at the device. Good pointer, thanks! I'll recalibrate tomorrow!

    Hi, I have a problem related to the original post. I have a very similar setup: I have a fairly recent POTY (i.e. with the cylindrical lens) on an Octagon Quad Green HQ in front of a 85cm offset dish. Reception using the POTY is fine and I am currently trying to tune it for transmitting. This is my patch:

    From what I've read here, the POTY can be characterised by some notch (for some around 1800MHz) from the reflector and, depending on your measurement equipment, either a double-dip slightly below and slightly above 2400MHz. or just a large dip around 2400MHz.

    Using a MiniVNA Tiny, the RL-dip was slightly too high for me in the beginning:

    After some round of gentle bending the result looks like this:

    which looks a bit better (return loss of about 19db at an SWR of about 1.3) and has some potential for optimization.

    However, my smith diagrams differ vastly from what I've seen on the BATC forum. This smith diagram corresponds to the previous RL/RP plot:

    which is similar to the results by some other people, except that the loop in the diagram is kind of blown up. When I look at the smith diagram over a larger frequency range, I get this:

    From what I see everything seems to be okay per se, but none of the other POTY measurements I've seen had multiple spiralling loops, so I may have made some mistake?

    (Btw: the loss in the last plot is slightly smaller because the patch probably bent back a little after around 30min, so I'll have to repeat the process)