I aim to start playing with RF and the first thing I wish to do is some EMI tests.
I've been watching YouTube videos on the matter as you do, and I've seen plenty of people using SMA connectors. This initially surprised me as I was for the most part only familiar with BNC connectors, so I went searching and found out why different connectors exist. They can have different impedances and most importantly different frequency ratings. Eventually I saw someone crimping an SMA connector onto some coaxial cable which lead me to go and see how expensive of an endeavor this was, and I found not expensive at all. I immediately found a 10-pack of connectors and a crimper for $30 on Amazon.
Upon trying to figure out what kind of coaxial cable they were using, I found people using RG58 and RG402. Later I found this chart with various coax cables and their characteristics. Looking on Amazon I found some badly reviewed cables with users complaining about the shielding being magnetic (meaning it wasn't copper).
Later I managed to find this article on optimal high frequency coaxial cabling, but still not anything that would mention a frequency rating of any kind. This was unlike the connectors, for which I immediately found a general frequency rating on Wikipedia.
Lastly I came upon this answer which explained resistive and dielectric losses are a function of length and frequency (for any given cable's characteristics).
I'm now thinking that no coaxial cable designation has any inherent frequency limitation.
It's all down to attenuation and length. As I have (perhaps wrongfully) concluded from the aforementioned answer, attenuation will go up with frequency (and length). And so for any specified maximum attenuation, the useful length of coax that will simply reduce as the frequency increases, but it will still work.
So if we're trying to determine the 'quality' of a coaxial cable, seems like to me that we should go for the one with lowest attenuation. The only other criteria for 'quality' of the coax appears to be the effectiveness of its shielding, and that too seems irrespective of frequency. So for instance LMR-200 would be objectively better than RG-58C (same outside diameters).
Lastly, it seems perhaps lesser metals in the braid/shielding would result in higher attenuation due to a faster increase in resistive losses, though I'm wondering if the comparatively large volume and surface area (as compared to the center conductor) wouldn't render the difference negligible. Otherwise if attenuation per unit length is a part of the specification then it seems to me the material will hardly be relevant in electric terms.
Is there a frequency rating for coaxial cable?
How do I know if I have good coax or poor coax (for the same designation)?