A time-transmitter is usually bundled with a time-receiver, but time-receivers are so cheap that they are usually standalone units without a time-transmitter. The best place to locate a... wait a second.
I really want to jump into the nitty gritty about time devices, but I guess I need to establish the background information first.
Here's the gist. The basics. The elevator pitch.
In order to jump from one time and place to another you need to jump from a time-transmitter, to a time-receiver. If there's no time-receiver, there's nowhere to jump to.
Time devices are great but they're not the same as the "Time Machines" you've read about in Science Fiction. You can't just zip through space-and-time, hither and thither, without a care in the world. You can only jump to a space-and-time where someone has conveniently placed a time-receiver.
"The telephone was invented in 1870 by Alexander Graham Bell. And as a means of communication it was totally useless. Until he invented a second one."
...and so it is with time-devices. One alone is of no use at all.
"What happens when you place a time receiver?" is a question you might not be asking. But you should be asking. Because it's a pretty fascinating experience.
If you're very lucky, then what happens when you place a time-receiver is this: it dissappears. Why does it dissappear? Because it is exactly where you left it. Not just in the place where you left it, but the time and place. So you placed the time-receiver on the ground. You pressd the little red button on the side, and you watched the red light blink three times. And then the device disappeared.
As I say, that's if you're very lucky.
If you're unlucky, something else immediately appears. It could be your own self. Or 14 different versions of yourself. Or an army.