This article describes a method of using an active external antenna with a GPS receivers that has no antenna jack. It consists of the receiving antenna, a power supply box, and a small "re-radiating antenna" that couples the signal into the GPS receiver's internal antenna. First, start out with a low-voltage low-power active antenna like the Mighty Mouse 2. This draws about 5 mA of current and it will operate at 3 V very nicely, for a total power consumption of 15 mW. The commercial re-radiating antennas are designed for use in a vehicle and don't worry about power consumption; they draw 20+ mA at 12 V, or 240 mW and more. Obviously, when you reduce power consumption by a factor of 15, you can use a smaller lighter battery. Because the antenna operates over a wide voltage range, regulating its own operating current internally, you don't need to supply regulated power to it. I would avoid a 5 V-only antenna because you'd need a voltage regulator. Then you'll need to pick a power source. The MM2 (and similar low voltage antennas) operate properly over a voltage range of 2.5 V to 5 V, so you will need something that operates within that range. The smallest lightest source is a 3 V lithium battery, for example the CR123 battery used in point&shoot cameras. It will power the antenna for a long time. A lithium coin cell would be even smaller, but give a lot less operating time. Or you could just use 2 or 3 alkaline cells in series. Two cells are marginal for voltage at end of life; you may have to swap batteries before they are fully dead. Three alkaline cells are perfect. Rechargeable NiMH cells are also fine, and 2 cells are enough (they provide 1.2 V until almost dead). Once you've picked the power source, you'll need a small box to carry the battery, a couple of connectors, and a few internal parts. Metal is strongest, but plastic is possible. You'll need to mount two RF connectors on the outside of the box, one for the receiving antenna, and one for the re-radiating antenna. BNC connectors are cheap and robust, but somewhat large and heavy. If I were trying for the smallest lightest package, I'd use SMA connectors instead - small, waterproof, and screw on so they won't come off accidentally. The internal circuitry in the box needs to look something like this (Use a fixed-width font to display the diagram) -- F1 L1 / \ ---######---@@@@@@-+---+-+ | IN + | \ / C1 | --- --- | 3V input --- --- | / \ +---+-+ | OUT \ / - --- -------------------------+ F1 is a small fuse. It can be omitted if you're using alkaline batteries, since their current output when shorted is limited. But it's a good idea to include it for lithium or NiMH batteries. Something like 1/10 A or 1/8 A is fine. L1 is an inductor whose job is to pass DC from the battery, but block the GPS signal so it isn't loaded by the battery. I hand-wound the one in my supply. It is 6 turns of #26 (0.4 mm) wire wound on a 3/32 inch (2.4 mm) drill bit shaft, giving a coil diameter of about 3 mm. The turns are spread apart by one wire diameter or more, giving a total length of about 6 mm. Since the turns of the coil don't touch, insulated wire isn't needed. In fact, the number of turns or the coil diameter don't seem to be critical either - any coil of about this size should perform reasonably well. Smaller wire than #26 is also acceptable. Capacitor C1 is a 47 pF ceramic capacitor. It passes the GPS RF signal from "IN" to "OUT" connector, while blocking the DC power provided from the battery. Thus, no DC is present on "OUT". Since the GPS RF signals must pass through C1, it should be a high-quality low-inductance capacitor. I used a surface-mount chip capacitor. A 100 pF capacitor would also work if you can't find 47 pF. The RF signal path between the two jacks needs to be built as a transmission line. You can either wire coaxial cable between the jacks inside the box (but note that capacitor C1 needs to be in series with the inner conductor, or use double-sided PC board to build a microstrip transmission line. The latter makes it easy to put a chip capacitor in series with the signal. If this sounds daunting, just mount the two jacks close together and solder an ordinary axial-lead capacitor between their centre pins. If the distance between jacks is small, you'll get away with it. You don't really need a power switch; disconnecting the antenna cable from "IN" will stop all current flow and preserve the battery. But you can add one if you want. Finally, you need a re-radiating antenna. You can actually use any passive GPS antenna for this (active antennas don't work in reverse). A cheap substitute is just a loop of stiff copper wire one wavelength (190 mm) long, which you can shape to fit the antenna area of your GPS receiver. This is what I use. I connect the loop to the power supply box with 3 feet of RG-174 coaxial cable. The centre conductor is soldered to one end of the wire loop while the shield connects to the other end of the loop. Other re-radiating antennas are possible; any method that works is fine. I'd suggest starting with the simple loop and making sure the whole system is working first. Then you can experiment with other coupling methods, testing whether they work by swapping between the loop and whatever you just built. Some possibilities: Someone else mounted the re-radiating loop plus electronic components on the auxiliary power plug for an eTrex. Another person just mounted metal plates in front of and behind the top of the GPS case, and used them to couple the signal capacitively into the internal patch antenna. (The loop works mainly by inductive coupling via its magnetic field). Note that, in use, the re-radiating antenna should be kept well away from the receiving antenna. If the two get close enough, the whole system may start oscillating at the GPS frequency. This would wipe out reception of the real satellite signals.