I tested the end fed half wave with the toroid transformer from the driveway today. The high end was 24 feet up. I worked K3Y/2 SKCC special event station using 2.5 watts. I got a 449 report. He was 910 miles away in Tuckerton, NJ.That is about par for QRP. So I am thinking this arrangement is good enough for the beacon rocket. There really is no way to know the impedance while it is airborne I just want to be as good as I can be to the transmitter.