Transmission1

I'm thinking I'd like to put a discone in the loft as I've just bought an RTL SDR V4, the coax run would need to come back down to the ground floor via a bit of a convoluted run, about 40 meters, maybe a bit more by my guess.

I don't want to use thick RG213 type cable as it's bulky, ugly and it doesn't go round tight corners well,

I've got most of a reel of 75 ohm sat cable, I was thinking about using that but, yeah 75ohm, not ideal.

I'd like advice and ideas on what would be the best 50 ohm option, about 7mm max diameter, fairly flexible and hopefully not too lossy.
Thanks
Neil

Use sat cable.
I use sat cable to all my rx antennas cause it's cheap and 75/50 Ohm doesn't matter in that case.
I also use 75 Ohm coax to my transmit antennas, but antenna must be monoband.
Chris

I use SAT100 or CT100 for all my receive antennas (and one or two tx ones, too), as it's good quality proper copper core and braid with extra copper sheathing. There's not a huge difference in price between the cheap and nasty basic sat cable and this stuff, so it's worth the extra, without paying much more for RG213, and the like.
For receive purposes it's ideal, with quite low loss.
Only slight embuggerance is the F-connector system isn't very reliable, so I have to fart around a little bit adapting connectors in order to get a good soldered end.