Is LNB cable meant to be 50 or 75ohm ? im wondering if this is why iv had problems linking in the past. Some sat cable is 50ohm where as TV coaxial cable is 75ohm.

75 ohms

Defo 75 Ohm, and decent low-loss stuff like RG6 or CT100 not the cheap white or brown stuff. I can get 20 Metres of RG6 for a tenner locally, 250 Metres for €40.

if 75 Ohm cable is used in a 50 Ohm system, the SWR would be around 1.5:1 in general, which means a mis-match loss of just 4%, so in the majority of cases it won't make much difference which you use, as long as the TX can cope with the SWR. RG-6 is lower loss than RG-213. The most difficult thing is that 75 Ohm cables rarely fit into 50 Ohm plugs properly.

XXL - the reason you've had problems linking in the past are more likely to be due to the microwave gear drifting with temperature, or because it wasn't correctly tuned (it's easy to tune to an image frequency or a harmonic).

I addressed the drift problem by always using an AFC system on my receivers. As the transmit frequency "wandered" through the day as the sun went past, the receiver would track the signal and stay tuned. I also used horn aerials to provide a bit more transmit power and narrow the beam angle. Physical alignment became much more critical, but the signal strength was substantially improved - especially useful if I was going more than a couple of kilometres!

Microwave linking can be very effective and quite difficult to track, but I never used it alone - it was always just part of a link system. I always preferred 45cm links - up in the UHF TV bands. There are still "wide-open spaces" up there, and high gain aerials are cheaply available from your local DIY emporium! It's a pity that most of the clowns building rigs these days haven't got a clue about UHF gear.....

@albert the link never drifts with AGD but I couldn’t get it fully linked in, there was still some static. And it’s impossible to link on a harmonic over long distances as they don’t travel as far as the main signal.

The AGD modules DO drift! They're not quite as temperature sensitive as the Solfan modules, but they definitely wander about....