Jumper T20 GEMINI: Fully-Featured ELRS radio!

The Jumper T20 GEMINI is the third model of the family, and as its name suggests comes with a built-in twin ELRS TX module. The T20G inherits the small form factor and full-size RDC90 gimbals of the T20S. In this review, we will discover all the differences and if it is worth the extra money.

Once you delve into the RC hobby, continual purchases become a norm, whether replacing a worn-out rig or meeting the increasing demands for enhanced performance. Based on my experience, the radio controller is the most stable thing of all accessories, so investing upfront in a proper one is essential. The Jumper T20 GEMINI will satisfy the requirements of any pilot for many years to come, especially since it can also be upgraded with an external TX module if a new standard is released in the future.

ExpressLRS is one of the most exciting control links, improving every day. ELRS GEMINI is a dual channel (2.4GHz OR 900MHz) radio system focused on much higher and stable LQ by simultaneously transmitting packets in two frequencies to increase the chance of receiving the pocket by the receiver. This technology was introduced in late 2023, and Jumper’s T20G is the first radio controller with a built-in TX module that supports this standard.

JumperRC T20 GEMINI review

Disclosure: I received this drone transmitter from JumperRC to test it and do an in-depth review. Although the RC was offered for free, all opinions in this article remain my own, with no influence from my partner.

The JumperRC T20 Gemini comes in a nice handbag with the following accessories: a neck strap, USB-C data\charging cable, three spare tension springs, flight mode button stickers, and a Quick Start guide. Additionally, they sent me four sets of CNC aluminum stick ends.

What makes the T20G unique is not on the outside but inside. Till now, all radio controllers had only mono\solo ELRS modules built inside with a max power of 1 watt. The T20G’s GEMINI ELRS TX module has a dual 1W (500+500mW) transmission power, providing the best anti-interference performance and stability. It is the ideal radio for demanding applications like FPV racing, Bando, and long-range flights. The TX firmware can be upgraded through the type-C connector or wireless via the built-in web UI. After upgrading the TX software, remember to replace the existing LUA script (elrsV3.lua) with the newer one.

Like all models of the T20 series, the Gemini edition also runs on the popular open-source EdgeTX firmware. A speaker under the left gimbal ensures audible alerts and feedback during your flights. It is a cool feature if you have the time to configure it well. The voice audio files are stored on the internal memory; no micro SD card is needed like in the case of other radios.

Key features

• Compact design with full-size gimbals and a variety of controls (1\2\3 position switches, rotary knobs\dials, sliders, and customizable flight mode buttons);
• Built-in Diversity GEMINI-compatible 1W (500+500mW) transmission module;
• OLED status screen;
• Long Battery Life with two 21700 Li-ion cells;
• Trainer port and USB HID work FPV simulators;
• Built-in memory, no micro SD required.

Technical parameters

Dimensions	~10x50x12cm
Weight	425 grams (without batteries)
Display	1.3″ OLED with 128*64 resolution
Gimbals	Full-size RDC90
Storage	Inbuilt 512 MB
Input voltage	6.0V – 8.4V
Battery options	2S LIPO, 2×18650, or 2×21700 Li-ion cells

JumperRC T20 GEMINI: RX compatibility

The T20G will work with any 2.4 Ghz ELRS receiver on the same major firmware release. Instead, for full GEMINI compatibility, you will need a dual-RF true Diversity ELRS RX module such as the BetaFPV SuperD or the RadioMaster RP4TD.

T20 GEMINI: Design, Ergonomics, and build quality

Instead of a gamepad-style design, the T20 series has a box form factor with an approximate size of 175x140x65 mm. Without batteries, the transmitter weighs 425 grams. Except for the new foldable and rotatable double antenna (DFA), there is not much change from the T20S on the front. It has the same control layout, OLED screen, and RDC90 gimbals.

On that back, instead of a metal heatsink, now there is a cooling fan (250 mW default threshold to start). The external TX module’s extension port (data+XT30 power plug) is in the same position behind a plastic flap. The extension (Nano\Micro) isn’t included in the package and must be purchased separately.

Gripping it comes effortlessly, and manipulating the controls requires no awkward finger maneuvers -everything is comfortably accessible. The backs of the handles have a nice non-slip rubberized finish.

The overall build quality is excellent for its price tag. The DFA folds ingeniously, saving space during storage. Most of the controls are labeled. The stick ends are replaceable (with m3 screw size), allowing users to upgrade them for better fill -whether they prefer pinch grip, thumbing, or hybrid pinching.

T20 GEMINI: Controls (Buttons/Switches/Knobs/Sliders/Dials/Trims)

The T20 GEMINI is the most complex radio controller I have ever had in my hand. If you are a DJI pilot, you will need a map to navigate on the front panel :) In addition to the two gimbals, it has six backlighted configurable flight mode buttons, two sliders (S3 and S4), and two dials (S1 and S2).  It has four tiny 5D trimming joysticks that can also be programmed in EdgeTX as control momentary push buttons.

There are two 3-position switches on the front (one on each corner) and two 2-position switches on top (also in the corners). Additionally, you have two shoulder metal latching push buttons behind the sliders with a center indent.

To control and configure the radio, there are three tiny buttons on the left and a scroll wheel on the right. To make a straightforward operation, the buttons have dual functions according to how you press them:

• Model Setup (short press), Radio Setup (long press)
• Next Page (short press), Last Page (long press)
• Back

I like the included stickers with function names (RTL\ACRO\AUTO\CRUISE\ and so on), enabling pilots to customize the six flight buttons to their needs. Here, I should mention that the buttons double as charging indicators and visual effects during power ON/OFF.

T20 GEMINI: OLED status screen

My biggest problem with the T-Lite, the T20’s predecessor, was the backlit LCD screen on which the tiny fonts were barely visible. While the screen size remained the same, the T20G now has an OLED screen ( 1.3″ with 128*64 pixels) with superior clarity even under direct sunlight.

The main reason I replaced the Jumper T-Lite with the RadioMaster Zorro was the small screen, so I would have liked to see a bigger screen on this new model.

What batteries are supported by JumperRC T20 Gemini radio?

The T20 can be powered from 6.0V to 8.4V. It has a generous battery bay (84x43x25mm) with a 3P XH2.54 connector. You can use a 2S LIPO battery (there is room for 1800-3000mAh) or two 21700 batteries using the included 2-cell LIION cage. You can also use 18650 with this holder by pulling the contacts inwards so they can hold the slightly shorter 18650 cells securely.

Power Consumption widely depends on TX power settings (15mW-1Watt) and Antenna modes (Single, Switch, or GEMINI). Using two 21700 4000mAh batteries, you can expect three to ten hours of operation time. Enabling “Dynamic power” in the ELRS LUA script gives you the best balance between transmission range and battery life.

The lighter 18650 batteries are adequate for a few hours of weekend flying, but those who fly all day and every day should use two 5000mAh 21700 LiIon cells.

Charging

The T20G has a built-in charging circuit, and the LIION cells can be recharged through the USB Type-C port on top of the radio. Initially, I tested it with a 100W PD charger but discovered it was not supported. I could use it only with legacy 5V USB chargers, known to be super slow.

Optimal TX power setting for Jumper T20 Gemini transmitter

As mentioned, the T20G claims to have a max TX power of 2x1000mW in Gemini mode. Setting the highest power does not necessarily give you the best range and penetration. Don’t mention the possibility of interference with your digital FPV system that runs on much lower power (10-700mW).

ELRS range test results show the possibility of flying as far as 50 km at 100 mW. For the best range, matching the orientation of RX and TX antennas is essential. For me, 250mW (dynamic power enabled) works best and covers the entire FPV range of my O3 Air Unit and Walksnail without a failsafe.

Oscar Liang, who also reviewed the T20G, measured only 500 mW when a 1W power output was selected. Hopefully, this is an isolated problem of its review sample or a software bug and not a hardware limitation on the power source side.

UPDATE: After I flashed the latest 3.3.2 ELRS firmware, the 1000mW was deactivated, and I could select only up to 500mW, whether you are in GEMINI mode or single antenna mode.

Pricing, availability, and accessories

The T20 transmitter can be ordered from JumperRC’s website for $199.99 (you need to log in to see the price) or from popular online retailers such as RC-Wing, HobbyRC, NewBeeDrone, and Banggood. You can accessorize the T20 Gemini radio with a transparent case and CNC Aluminum stick ends.

T20 GEMINI Diversity: Who’s for?

Most FPV drone pilots will probably not use even half of the control options available on the Jumper T20G. Instead, giant-scale RC planes and turbine guys will appreciate the variety of controls and the number of channels. Channel trimming is also beneficial for fixed-wing pilots but is mainly useless for multi-rotor flying machines.

If you are mostly into proximity park flying, the extra price for the GEMINI technology advantages is not justified. Also, if your drones are equipped with “mono” ELRS modules, there will be no difference for you.

T20 GEMINI vs T20S vs T20: What’s The Difference?

JumperRC released the T20S and T20 in the summer of 2023 and the T20 GEMINI a few months later —the difference between the first two models being only the gimbal (and, of course, the price). The basic T20 has hall sensor (magnetic field) gimbals, while the premium T20S boasts potentiometer (analog output) RDC90 gimbals. The newer T20 GEMINI also uses RDC90 joysticks, but the internal ELRS receiver now has Diversity dual-transmission modules and double-folding antennas. To handle the extra heat, the GEMINI has a cooling fan on the back, as mentioned before.

Of the three, the T20 is the cheapest model, priced at $109.99. For the RDC90 gimbal in the T20S, you will need to pay extra $30 bucks ($139.99). The T20G is the flagship model of the series, and it is priced at $199.99.

Jumper T20 GEMINI: Alternatives

If you want a feature-rich ELRS transmitter with built-in GEMINI capabilities, your only option is this T20G. If you don’t mind, use an external module such as the BetaFPV SuperG Nano TX that provides the same transmission capabilities; you have plenty of good options, even for less money.

RadioMaster Pocket is the closest in design and format factor to the T20 GEMINI. Priced for only $64.99, it is an excellent budget alternative.

The RadioMaster TX16S and Jumper T14 are also great alternatives but on a larger form factor. If size and weight are more essential for you than extra functionalities, the Jumper T-Lite is a bargain for mare $59.99.