I'm making a dog health and activity monitor with 2 Micro:Bits. I found out that the radio range is only 70 metres, and I need to make it about 5-6 KM. I was wondering whether I could connect a loop antenna to the Micro:Bit. If so, how would I do that? Could I use an amplifier of some sort? I'll take any advice at all. Thanks.

 

Most likely you cannot do that without violating the laws governing unlicensed radio in your country. Most of the unlicensed transmitters used around the world conform to international treaties and are tested under very specific conditions including things like power output and antenna gain. They are usually intended for short range communications. to minimize concerns about interference. Most likely anything you do to extend the range will render the transmitter illegal.

5 to 6 km seems a bit beyond even Lora equipment.

 

dog is domesticated animal. so even after wandering around it keeps returning to home of the human. at that time short range is more than sufficient. all you need to do is buffer stored data and only transmit when in range.

the other option is to leave transmitter as is but add repeaters or use large directional receiving antenna that keeps lock on the wandering dog.

 

Longer range devices are available, some include GPS to report the actual position. BUT they are far from cheap. Some are made with a magnet to attach them to a car. And the receiver that is used with them is even more expensive.

 

Or...don't you dog wander around. Depending upon where you live, there may be many things that can injure or kill a wandering dog, so it is best to keep the dog behind a fence or as in my younger days, in the apartment.