It's known fact that trackers/beacons laying on the playa ground have a very low range.
What is your experience, is there a difference if the antenna is on the ground vs beeing 2ft above the ground?
I'm thinking of making an object/ball similar to BB-8 from StarWars where the antenna will always be on top. I'm aware that this would only work if the landing point is flat surface but it's something to try.
Thx
Field and lab studies have actually found that as an antenna approaches the ground, the vertical radiation pattern is reduced parabolically. For example, imagine that your antenna is, say, two metres above the ground. The vertical radiation pattern would be represented by a broad parabolic distribution (signal falloff vs distance) where the received signal strength falls off slowly as your signal path increases. Now, if you
decrease the antenna-to-ground distance sequentially, the parabolic shape narrows accordingly, with the received signal strength falling off more rapidly over the same signal path distance. There would be a wavelength dependence here and I suspect that this effect is less at longer wavelengths. In your case, where you are on the playa, the effect is less than if you are in crop fields, where the attenuation will be higher. There is also the question of available transmit power. There are limits to this if you are operating in the ISM or LIPD segments of the spectrum, depending on the country of operation. Radio hams have a little more freedom here.
There are measures you can take to reduce this effect that are to do with antenna selection and installation. The antenna of choice is typically a monopole because it is generally very effective, cheap and easy to install in the rocket. This raises the question about how and where you install your monopole antenna. The best place to install it to ensure that your radiation pattern is optimal is in the RF transparent nosecone where there is least obstruction and loading by conductive components. However, many rocketeers like to install their antennas in the avbay, or perhaps on the outside of the avbay bulkplate. These locations are not ideal and lead to distortions in the radiation pattern due to adjacent conductive items, such as threaded metal rods, deployment links and eye-bolts, altimeter PCBs, etc.. While in flight, these distortions in the radiation pattern are probably not that critical because the rocket is generally rotating. However, when the rocket is lying on the ground, this might adversely effect an already compromised radiation pattern. The orientation of the rockets' antenna with respect to the receiving antenna could be that the line of sight is such that the rockets' antenna is pointing a null towards the receiver.
What to do? Well, some rockets employ a few stub antennas on the outside of the body. So, in this case, your rocket will always present an antenna on top, regardless of its orientation when it lands. Another method is to employ a cylindrical patch antenna array on the outer surface of the rocket. Obviously, you will still have the potential issue of the proximity to the ground, but your radiation pattern will be better to start with and your chances of locating the rocket improved.
Another method you can consider is a dual polarity antenna arrangement on the rocket - if possible - where you employ two short monopoles with vertical and horizontal orientations. This would work better at the shorter wavelengths, say in the 900 MHz bands, due to space constraints. Obviously, you would also employ a suitable receive antenna, such as a crossed Yagi. Of course, when using multiple antennas, you will require a suitable power divider module to feed each antenna from the one transmitter.
