Unfortunately I'm not getting too much improvement over stock antenna.
all test done at 120m height
original antenna in town 600m and in field 1400m
Now with "6dbi" antennas in town 750m and in field 1750m.
I also tried "8dbi" antenna which is longer but result is worst than 6dbi.
Any suggestions?
Thanks
Improving from 1400m to 1750m is surprisingly good for just changing the antenna from 3dbi to 6dbi. That's a 25% distance improvement, and while 6dbi sounds like double 3dbi, it's not that simple.
There's a couple of things that you might want to know about antennas:
First of all there's no free lunch. A passive (un-amplified) 6dbi antenna is not going to double your range by ANY stretch of the imagination. There could be some modest benefit increasing size and getting it farther away from the remote and into free air, and added directionality which I suspect is the biggest improvement. But the size needs to be
appropriate for the wavelength, ie frequency.
Second, directional gain. Remember that
signals decrease in amplitude by the square of the distance (inverse square law). An
omnidirectional antenna radiates or receives equally in all directions. This is good where you have no way to orient the antenna in the direction it needs, but it's obviously less efficient because you have energy radiating directions that are unneeded. So for something like a 6 dbi antenna, it's going to be directional—that extra energy comes from somewhere, and it comes from the nulled direction—so, if you're not pointed correctly at the drone for your antenna's directionality, you're much more likely to lose contact.
Third, "db or not db, that is the question"... The internal antenna and the RC is a 3dbi antenna as I understand it. A 6dbi antenna is NOT going to double the effective strength or range. Doubling a 3dbi antenna would need (I think) a 12dbi to 15dbi antenna. Without amplification, that's going to have such a narrow beam, it's going to be hard to keep the controller pointed at it effectively.
Fourth, Signal polarization. Terrestrial Wi-Fi is most typically linear-vertically polarized. Looking at the photos of the internal antenna of the RC the antennas look like they are dual-horizontal+vertical. (some drones, and for instance
FPV goggles are circularly polarized (CW or CCW)). For a vertically polarized signal if receive side is 45° off results in about a 3 db loss.
Fifth, impedance, the transmit and receive circuitry in the remote control is going to be designed for a specific impedance antenna, so any antennas that you yourself decide to modify it with, need to be of the same impedance as the circuit was designed for.
Sixth, the total TxRx system. It's not just the remote control after all, you also have the drone out there which has its own transmit and receive circuitry and its own transmit and receive antennas. I think some of the enterprise drones can have added Tx boost modules added (some of those drones are in the $15,000 + range...) For the consumer level Mavic/Mini etc, such an active mod is not just going to add weight, but also subtract from flight time, (not to mention questionable legality, your mileage may vary, different nations have different laws on that.)
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Your setup: those look like the kind of antennas that are just on a home router. If they are, then they're probably just vertically polarized. Orientation can have an effect. Same is true for your 8dbi antennas, no I suspect that you got worse range with the 8dbi because they were substantially more directional, (read: narrower beam) and the drone was slipping out of the beam.