Belden has a maximum cable length chart for different cable types and video signal bandwidths:
https://info.belden.com/hubfs/resources ... lletin.pdfSo for 1505F, Belden recommends a maximum cable length of 46m with 3G SDI signals.
In order to support higher bandwidth 4K/Ultra HD video (up to 12G SDI), Belden has introduced a range of cables with better attenuation specs. These typically have product numbers starting with 4xxx and should result in better performance for lower bandwidth signals as well.
So with Belden 4505R which is a similar thickness RG-59 type cable, Belden claims you should be able to do up to 66m @ 3G SDI which is actually a bit better than some of the thicker cables of older design (1694F or 1695A, for example). One other thing you might notice is that the flexible versions of the cable like 1505F or 1694F tend to perform a bit worse than the stiffer equivalents (1505A or 1694A). One other factor is that well used cables that have been flexed or bent multiple times will often not perform as well as brand new cables.
One other note is that in newer versions of the SDI specifications (SMPTE ST 425, 2081, & 2082) used for 6G and 12G SDI, they changed the maximum insertion loss threshold to 40 dB loss at 1/2 the clock frequency (up from 20 dB in the older HD and 3G SDI standards). The bottom half of the Belden cable distance chart uses this threshold, which are why the maximum cable lengths are longer for the same signal type.
So in theory, 6G and 12G SDI hardware designed to meet these newer standards should also perform better with 3G or HD SDI signals as well. And occasionally I have found this to be the case, and a cable that didn't work with a 3G-only input receiver did work carrying the same 3G SDI signal into a 6G or 12G SDI capable input receiver. So sometimes you can put a 6G SDI to HDMI converter (with the loop through output) or a 6G SDI distribution amplifier at the end of a long cable run, followed by a shorter run to the actual 3G destination. This doesn't always work of course, but can sometimes be worth trying if it's difficult to swap out the cable.