Chris wrote:

In article , PoP
writes

trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection


All I'm trying to do is to make the aerial longer,
without high ladder work.
I'm not splitting it.
I just want it to go to a room further away from the aerial on the roof.
And - it's FM radio - if that makes a difference.


Not much difference.

The issue is, as has been pedantically stated, one of reflection. This
may set up resonances in teh stubs to each side of teh joint, so that
some stations arer stronger, othgers weaker, depending on frequency.

However we used to join cables a lot in test situations, and the VSWR
was never high enough to be a significant problem.

Do it, and if its seriously ****e you can blame me and do the job
'properly'. But you won't need to.