Winston
Lorenzo von Matterhorn
- Joined
- Jan 31, 2009
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For my own use and because of the radiation pattern and polarization issues I already knew about, I was thinking about its use in a DIY LoRa module launch system I'm thinking about creating, one dipole contained in the lid of the launch controller and the other in leading edge of the closed and waterproof pad box which would be, for safety reasons, 15 feet from the launch pad along the route to the RSO table with the "remove before flight" flagged launch current enable pin in it removed on the walk back to the RSO.Two things, if one uses a screw on vertical dipole on their 915mhz tracker (most all the aftermarket screwons for this frequency are vertical dipoles) with the rocket pointed skyward one would have to hold the receiver horizontally to match polarity for max range. If one's rocket falls perfectly 90 degrees to the ground (ie. horizontally) then a horizontal position like as shown in the picture is optimal. S.B. you might have mixed results with video on a 2.4 gig
Yagi because the beamwidth at that frequency is narrow. The drone guys use 'em for long range control but
they don't move like rockets. Video is better served by circularly polarized antennas like the cloverleaf design.
I bought a pair for 915mhz but it would take a 5.5 to 6 inch diameter tube to contain it. Darn! The picture looked small! Kurt
Yeah, the only real benefit of the dipole would be the lack of a need for a breach in the pad box, but a vertical is trivial to make, dirt cheap, and a rubber BNC boot and rubber washers in the right places should prevent leaks. Just in the "what-if" stages right now.Yeah but.......... That reference is for HF and when doing VHF and higher the behavior is different. Nonetheless, best of luck and post pictures. I would suspect that if a suboptimal antenna were used, LoRa would take a bigger hit than if the tracker were higher powered.
I got two (only needed one) of these commercial grade 915MHz outdoor patch antennas for less than the price of one (normally $42 each) and made a camera tripod mount for it for a rocket telemetry ground station:Yup, you're right about the Chinese stuff. I did pick up some reputable 900Mhz Yagis that were brand name on the cheap as they were NOS and I suspect the resellers didn't know how much these things went for originally. The one 5 element Yagi is pretty well built and heavy.
Yep. Circular polarization is best for anything that's not in a fixed orientation.Circularly polarized antenna system would be ideal for rockets for when the tracker is flopping all over the place from a high apogee descent. The problem there is the size of a circularly polarized antenna.
It might be more than just that. Polarization mismatch should "only" cost 3db, but if you're right on the edge of the minimum required RSL that's enough. Periodic end-on or near end-on orientation of a flight antenna would cause huge dropouts.Me thinks polarity mismatch is the reason I see drop-outs with the 100Mw, 915Mhz stuff and even the
low powered Beeline GPS trackers on 70cm.
Video is better served by circularly polarized antennas like the cloverleaf design. I bought a pair for 915mhz but it would take a 5.5 to 6 inch diameter tube to contain it. Darn! The picture looked small! Kurt
You only need a circular polarized antenna on one end.
Going from linear to circular polarization does cost you a 3dB polarization loss but it is fixed. Unlike the variable losses when linear polarization antennas move around.
Circular polarization comes in two flavors: left hand and right hand. Naturally if the transmit and receive antennas don't match you get high losses.
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