Dipole PCB Antenna Overview & Usage Tips

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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
 
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
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.

Because of the long range of LoRa modules, a vertical on both units would be adequate, but the horizontal orientation of the dipole would allow what I just described - no visible antenna anywhere and no holes in the very small waterproof pad box to attach an antenna which in the case of a vertical would be attached on the top of the box using a BNC with rubber BNC boot with a ground plane under it in the lid. Plus, the PCB dipoles will be antennas with known, very low VSWR. The dipole antenna in the RSO launch box would be many wavelengths above ground, the pad box antenna less than one.

Just an FYI on eBay antennas, never trust one originating in China which is pretty much all of them. Odds are that for any antenna where the radiating element is hidden as it is with most of them, it will be an antenna tuned for 2.4GHz (wifi and R/C transmitters) no matter what frequency they claim for it. NO ethics whatsoever... Anywho, creating a proper DIY vertical for 915MHz would be cheap and easy, so why buy one from unethical thieves?

That said, a vertical antenna has a lower takeoff angle providing higher gain at lower elevations, so it might be six of one and a half-dozen of the other...

https://wb2lua.com/papers/HF_Antenna_Analysis.pdf
 
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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. 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.
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.

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. Polarity mis-match can be overcome a bit with "more power" but fortunately for rocketry, once the rocket settles down under the main chute, positions are more reliably decoded and
allow us to "get 'em back". One could argue it would be smart to blow a main chute (with a GPS tracker) as high as one can tolerate to take advantage of propagation at altitude and allow a drift trend to develop. Of course that would
depend upon the launch venue and the flight profile.

I've conclusively proven to myself that a 900Mhz Yagi will give one a larger ground footprint at least with the EggFinders. One can prove that to themself by using a Yagi when going out to recover. Once the signal comes in, take off the Yagi and
screw on a vertical dipole. The three times I tried it, the signal dropped out. Maybe not important for sport fliers but the larger ground footprint might be useful for a successful recovery of a far ranging project . Kurt
 
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.
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.

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.
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:

https://www.streakwave.com/mmSWAVE1/Video/ARC-PA0913B01_DS_090811.pdf

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.
Yep. Circular polarization is best for anything that's not in a fixed orientation.

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.
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.
 
Ahhhhh, but the patch isn't a Yagi and definitely offers benefits!:) Hmmmmm, I had a picture of my 900Mhz patch on a pole but apparently all the pics I saved to TRF are gone now?
I can vouch for a patch with a vertical dipole on the tracker. It improved reception quite a bit.

Kurt
 
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.
 
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.

Right, hence the reason my patch antenna on a pole improves reception of the EggFinders that use a Linx vertical dipole on an SMA connector on the tracker end.;) Kurt
 
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