How do you track other travelers in hyperspace?

[Dev Corvin]

It's not actually "hyperspace", it's "subspace", as Sam actually says to McKay's sister in McKay and Mrs Miller.

As we know from the fact they have subspace communication devices, used for communicating between the Daedalus and Atlantis on a regular basis, it's evidently possible to monitor subspace for "subspace signals" (similar to the effects of a field emission), therefore it makes sense that any form of electromagnetic emission into subspace would also be traceable.

The most likely possibility is that the Asgard computer core emitted a frequency higher/lower than their standard equipment which travelled further through subspace and was therefore easier to detect.

If you're having difficulty grasping it, imagine when you switch on an electronic device (any device, in your home); certain people have the ability to "hear" the device... the best description for those of you who can't is like a high-pitched whine, almost undetectable but present nonetheless. Different devices/voltages/polarities give out a different EM signal and some are more easily detectable than others.

[Heaven]

sounds plausible, good job

[YodaMate]

Indeed, subspace transmissions are easy to pick up unless you have the tech to encrypt it ; way back in Season 2, the Goa'uld spy amongst the Tok'ra was revealed because he had a ball communicator, which the Tok'ra didn't use because their transmissions could get picked up too easily by the enemy.

However, Atlantis and its puddle jumpers have the ability to encrypt (which i guess means disguise so it appears like subspace 'junk') their transmissions so the Wraith couldn't detect them, if i recall correctly.

The Asgard can watch other ships in hyperspace ; in the Season 4 premiere, where Carter advises luring a Replicator ship into hyperspace and destroying it, she and Thor watch the action in real-time (very cool zoom-out effect too, by the way ).

I would assume the Ori ships can do the same, but they need to be in real-space to track them, i don't think much of anything works in hyperspace because the ship is completely encased in its "bubble". However, the energy signature was so distinctive that it could be tracked by ships already in hyperspace.

Odyssey was damaged and couldn't do a straight-line race back to Earth and the protection of the Ancient drones. The Ori could catch up extremely quickly because they didn't have to drop out of hyperspace, get an update on where Odyssey was heading and then jump again, instead they could just follow and drop out when Ody did.