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(First of all, I hope this is the right subform, please correct me if I'm wrong)

I am using a 433 Mhz LoRa Radio to communicate with a high altitude balloon and am using an antenna like in this guide

I know many people have the antenna facing straight down (with radials attached to the bottom of the payload). However I want to use a satellite tracker as a backup, which means the tracker should always face the sky. If the antenna were at the bottom, the payload would probably fall over when landing... Would it be bad for reception, if i just put the antenna on a side of the payload instead of the bottom? (meaning the radials would be taped to one side of the payload and the antenna would be horizontal). As the HAB will be bobbing around a lot in the wind, would it even matter in which direction the antenna faces?

EDIT: Might the way of attachment shown in the picture be a solution? Possible solution?

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  • $\begingroup$ What is the orientation of the antennas with which you are trying to communicate? $\endgroup$ – SDsolar Apr 27 '17 at 5:43
  • $\begingroup$ Its mobile, so I guess you could point it in whatever direction is best? $\endgroup$ – user5227744 Apr 27 '17 at 15:00
  • $\begingroup$ @user5227744 How big is the package you are lofting and does it use any metallic surfaced foam in its construction? Or for the thermal properties of same? $\endgroup$ – Rowan Hawkins Apr 28 '17 at 4:09
  • $\begingroup$ Roughly 40x40x40 cm or so. No it does not contain any metallic surfaced foam. Only a bit of circuitry and a camera $\endgroup$ – user5227744 Apr 28 '17 at 12:52
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It sounds like you really have TWO questions. 1) should I use the existing standard or is there a better choice. 2) will the Sat Tracker antenna receive interference from the part 1) antenna.

I'm going to address these in reverse order. The satellite tracker should probably use a fairly wide patch or sector antenna mounted on the top of the cube pointing up. You could mount it inside as well since your cubesat design is essentially rf transparent.

Sheets of metal are opaque to RF which is why I asked if you were using aluminumized foam. [You may need change this depending on you're local aviation regulations for untethered balloon launches.] You want to not block the GPS receiver from seeing the sky. The balloon will be effectively transparent.

If you are using the monopole with radials, then these antennas are both on different frequencies and mostly in the null of the monopole so you shouldn't expect much interference.

For your ground pointing antenna. The 1/4 wave monopole is probably your best bet from a cost and weight standpoint. A package lifted by balloon has a stable up and down but rotation is impossible to predict. This is why the monopole is useful because it's radiation pattern perpendicular to the antenna element is the same in all directions. Its also a vertically polarized signal. Meaning receiving it on a normal vertically polarized antenna on a vehicle keeps the polarization the same for best reception. With this type of antenna the null or worst place to be is directly underneath the balloon.

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  • $\begingroup$ I did some checking of other types of antennas as well, but anything with more directiviy has related nulls, higher gain verticals cause the null area below the balloon to be wider. Inverted V is probably too orientation specific. a loop antenna would have better down directivity, at the cost of signal to the sides, it would also produce a horizontally polarized signal which means that you would need to change your receiving antenna to horizontally polarized as well. The losses from mixing polarization are quite steep. $\endgroup$ – Rowan Hawkins Apr 30 '17 at 20:52
  • $\begingroup$ Thanks for your answer. The trouble with mounting an antenna on the bottom of the payload is that it would make the payload tip over at landing, meaning the satellite tracker would no longer face the sky and loose its signal. You said that The styrofoam is rf transparent. That made me think, maybe you could mount the antenna like in the picture I added to the question right now (see above). Would that work? There may be some circuitry directly below the 2 radials which are on the top of the payload. $\endgroup$ – user5227744 May 2 '17 at 11:58
  • $\begingroup$ With the antenna made as suggested, it will likely fold over on inpact to the ground. Were you to install it the way you have on that picture you would stand a pretty good chance of completely detuning it because now the contents of the box are inside of the transmission plane as opposed to below it or in this case above it. You'll end up with three antennas per one for the SAT tracker, one for the GPS and one for the downward-pointing radio. Once the unit is on the ground you won't be getting updates for position but you won't need them either because you'll have the last update of position. $\endgroup$ – Rowan Hawkins May 2 '17 at 13:01
  • $\begingroup$ Your building something that is approximately a Cube. Unless the contents are perfectly centered inside of it, it's going to bounce around like a loaded dice when it hits the ground. This will not be a gentle parachute landing because there is no parachute. The other option is it will get stuck in a tree and you have to go find the landowner to find out if you can cut down the tree to get it. $\endgroup$ – Rowan Hawkins May 2 '17 at 13:27
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Advantages of the upside-down monopole include:

  1. It's omnidirectional in the azimuthal plane, so as the balloon rotates the antenna gain doesn't change much.
  2. The gain is higher in the down direction towards Earth.

The ideal radiation pattern of a monopole like this is a bagel sliced in half, with the monopole sticking through the hole in the center. With a ground plane of finite size it changes a bit but this is still the general shape.

With the antenna mounted on the side, half that bagel will be pointed up to the sky where you'd just be receiving noise (though not much of it since there aren't many radios up there) or wasting transmitter power. And as the balloon rotates the pattern changes: when the antenna is on the far side of the balloon relative to your base station, gain will be pretty low.

This may or may not be a problem. Ultimately it depends on the reliability you require and your link budget. You can use antenna modeling software to estimate the antenna gain, or build a prototype and test it empirically.

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