AO-85 Twist Trick and Other Hints

Right before launch a connection or trace leading to the antenna broke. The person who had the experience to resolder it wasn’t available and with the little time they had left they chose to use an electrically conductive epoxy to fix it. After launch, satellite operators noticed it was hard to get into the bird with the popular Arrow II antenna and 5 watts. [1]

Apparently the epoxy caused a change in impedance which essentially “detuned” the antenna. It makes the bird appear deaf. A workaround is to twist the Arrow antenna 90 degrees when you transmit. That is, rotate the antenna until the receive signal is “peaked” and then rotate it 90 degrees when you transmit and back again to receive.

AO-85 has simple vertical radiators, and since the Arrow antenna has its VHF and UHF elements crossed, if you “peak” the receive, then the transmit polarization will be 90 degrees off axis. When you’re cross polarized you lose signal. The fix is to just rotate the antenna.

The downside to this is if you’re working full duplex when you rotate the antenna 90 degrees to transmit you will often lose the downlink signal and not be able to hear yourself. In my experience I only have to do the twist trick in the beginning and end of the pass when the bird is farthest away.

Another fix is to just use more power, but if you only have an HT that’s usually not an option.

 

  1. http://www.amsat.org/pipermail/amsat-bb/2016-August/059850.html
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