Impossaerial, with Lupins

Before the roofers start on the last section of the house I thought I'd sort out which aerial wires were relevant.  Simple, surely. I know there's an amplifier in the loft, handily by the hatch, with a suitable number of cables coming off it.

I rig up a shorted-out connector and disconnect all the cables from the amp. Cupcake works round the rooms while I see which cable shorts with my meter back at the amp.

OK, so explain this...

There is one input cable and 7 output ones.

4 of the output ones go to particular rooms (remember we're a B&B).

3 of the output cables don't go to anywhere that Cupcake plugged the shorter into, so, like the telephone wiring I have three spare ends...  I really should not have been surprised.

Now the weird bit.

3 rooms lost their TV signal but were not those 3 cables.

Plugging ONLY, and I really mean ONLY, the input cable back into the amp, restores the signal to all three TV's.

Like, how does that work?

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I'm thinking mooncoin may have the answer.

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Meanwhile, back on planet normal, we very much enjoyed the performance of Dear Lupin at the theatre this evening.