Impedances and transmission line effects...

[Mark Hennessy]

With RG58 at 58pF/m - let's call it 60pF...

Twisted pair is likely to have a rather greater capacitance per unit length than RG58, I would suggest.

Yes, somehow I missed that Cardigan said twisted pair. My bad

Now let's look at the instance of trying to send 2MHz down a screened line 15m long, where the only known quantities are that (a) it's aircraft grade, and (b) the capacitance of the cable.  We can ignore (a), on the basis that the electrons don't know that they're at ground level.

Just by way of a "heads-up", please allow me to point out that because you're new to this forum - and therefore we haven't yet got to know you - it's hard to be sure whether this last sentence is humour or sarcasm. As written, it could be taken either way. With a smiley at the end, I'd certainly chuckle

2MHz corresponds to a wavelength of 150m in free space, so rather less than that in screened cable.  Someone upthread said that you need to start thinking transmission line theory if the line length approaches one-tenth of a wavelength (not the figure I would use myself, but never mind).  Mmm, 150/10 = 15.

Well if Trevor's tie-line gives him grief at 2MHz, I've no doubt that Trevor will know full well that he needs to terminate it. Certainly, we've established that it's absolutely fine for audio...

So if not 1/10, then what's your preference, and why? Some say 1/4. Interested in your thoughts...