Polarization Losses on QO-100 Uplink

  • Hi Peter-DJ7GP,

    nice experimental work. Could you kindly describe the last polar diagram in more details and in English please? I guess, that it is a polarization envelope diagram, isn`t? What are the magnitude units (dB)?

    Thank you.

    73, Rasto

  • Hi Rasto,

    usually we (Peter, DG5ACX and me) do the antenna measurements outdoors with the arrangement shown in the picture. To measure the circular polarization, the antenna rotor is tilted by 90 degrees, so that the antenna to be examined can be rotated by 360 degrees about its own axis.

    In the present case, however, this was not possible due to the rainy weather. We therefore carried out the measurements in our club room on a wooden table. Arrangement of objects 0.75 m above the table. Distance of the objects 1.30 m. The comparison with old outdoor measurements showed a good agreement. Since the rotor was not available, we rotated the log per transmission antenna by hand in steps of 45 degrees.

    The connection of the measuring points by straight lines is certainly not professional. The scale in the diagram shows the values in dB.

    73! Peter, DJ7GP

  • Hi Rasto,

    yes of course I will provide you with the measurement results as soon as we have carried out the outdoor-measurements.

    Of course you need the construction data of my duo band feed for the simulation. I would like to send them to you by email. My email address is: call (at) darc.de

    73! Peter, DJ7GP

  • Hi folks,

    I recently modified a few Airlink 60 antennas (see figure 1). This industrial 2.4GHz antenna is made by SSB Electronic. The original antenna has a vertically polarized patch in it, made by GlobeSat in Denmark. This patch is glued in the focal point to the inside of the radom (see figure 2).

    I replaced this patch with a WA5VJB-patch, LHCP (Hi Z to compensate for the effect of the radom, as recommended by WA5VJB), so that the antenna is transmitting right hand circular polarization (RHCP) (see figure 3).

    As I have a few of these antennas available, I could directly compare the circular antenna with the vertical linear one. The difference I measured in my QO-100 signal strength was between 2.1 to 2.5dB.

    Best 73

    Holger 'Geri', DK8KW

    Figure 1: Airlink 60, an industrial prime focus dish made by SSB Electronic.

    Figure 2: The inside of the antenna can be accessed from the back. Here, the original linear (vertical) polarized patch can be seen.

    Figure 2: The original patch was replace with a WA5VJB patch.

  • it was me who brough mike to the idea of the square with the cut corners (i have no lathe so peters feed was not easy to reproduce on the kitchen table) .. i calculated in sonnet lite and mike calculated in cst studio ... and end result was near identical

    rest is history

    difficult to build and tune ?? yes a bit ... but when exactly made shows a good circular pattern and is near spot on