With Captain Archer stranded on the Suliban space station, promising T'pol to get the transporter temporarily rated for humans within five minutes had got the Doctor access to exactly the equipment he needed. Even this century's Earth sensor equipment should be able to track tachyons well enough for the Doctor's purpose, with a little work. And redirect them ...
"What are you doing?" Tucker demanded, watching him work.
"Cross-circuiting the resolution wave," the Doctor lied. He'd have one shot at putting things to rights, analyzing the ambient time field and then restoring it; unfortunately that would probably not leave enough time for actually making the adjustment to rescue Archer from the Suliban space station - but once the Doctor's fix took, Archer should never have been in this situation in the first place, so the Doctor was doing as he'd promised T'Pol - from a certain point of view.
"Vulcan science officers," Tucker grumbled. "Alien ship's doctors. ... Stowaway transporter engineers."
There had to be an artificial time field overlay, but the Doctor couldn't just assume there was despite the overwhelming circumstantial evidence. He finished rewiring the plasmic scanners. Here came the tachyon readings ...
"Ship was supposed to be a human ship," Tucker went on.
What abysmal processing time! Finally. Was there a time field overlay? ... Yes!
No!
There were two!
"Not that I got anything against aliens - but a man's got to solo sometime."
And the second overlay was redirecting the time field - with an artron wave!
"How else does anyone get to see we're worth having as an equal partner?" Tucker concluded. "Hey," he yelped as the Doctor ripped out his makeshift tachyon converter, "you know what you're doing?"
"Your captain will be fine," promised the Doctor. Now that he wasn't going to be jury-rigging a reversion wave - because there was one already there! - he'd have time to upgrade the transporter after all ...