For VHF and UHF antennas you may find that HAM satellites are handy for this task too.
Depending on your location, some LEO bird will pass over your antenna at a good selection of elevation angles. The best pass is one that puts the satellite as much above your head as possible. An FM satellite is even better, since it provides a carrier of constant power, like AO-51 downlink on 70 cm.
So, make a prediction of an usable pass. Don't forget to check the satellite operating schedule, if any. Draw or print or write down a selection of time, elevation angle and frequency +/- doppler. Azimuth is not relevant if your omnidirectional antenna has a clear view of the horizon. Sit back and wait. Then look closely at the S-meter (better if analogue).
So far I have received AO
-51 UHF downlink on two antennas, one shorter than lambda/4 and one 3/4 wave (a VHF whip). Both magmounted on the car. At a certain point I noticed AO-51 signal at S2 on my S-meter with the VHF whip, as much as I could get with the Moxon beam!Back to the computer, I used MMANA to simulate this antenna at UHF. It was not a surprise to see that at 45° elevation this antenna has a 5.5dBi gain. Moxon rectangles are said to have about 6dBi gain, so we're in the ballpark.
As a conclusion, I can say the 3/4 lambda at UHF is good to receive almost any AO-51 pass above 10°. Unfortunately it is not enough to hit the satellite repeater with 5W. With a proper S-meter, the vertical radiation pattern of an antenna can be drawn per-points.
