N connectors are capable of handling much higher frequencies and power than BNC. They also provide a more stable connection due to their threaded coupling instead of BNC's bayonet coupling. A more stable connection will only be noticeable in unusually precise measurements. At a maximum frequency of 500 MHz, there won't usually be any difference.
I wouldn't expect good RF performance from either of those cables.
In general, a BNC connector that's missing the internal insulation is 75 ohms. This is typical for video cables which only have to handle a few MHz. Note that 75 ohm BNC connectors are capable of much higher frequency with no problem at all. Video cables don't really need much in the way of high performance. You often see 50 ohm connectors on 75 ohm cable and it seems to work okay.
The first cable you linked to appears to be doing something odd to reduce the diameter of the outer connector. Will it measure out to 50 ohms rather than 75 ohms? Who knows?
The second cable lists RG-59 cable, which is 75 ohms, yet claims the cable is 50 ohms. There might be a similar oddity in the diameter of the outer connector. The picture isn't very clear. The 75
foot length is an unfortunate confusion factor.
Neither gives good specs for the cable itself. Unfortunately, that's quite common for pre-made patch cables. The cable itself is often very poorly made with very poor shielding. Depending on your local RF environment, that can cause major problems.
You might want to buy a chunk of good cable and either crimp or clamp connectors and make your own patch cables. That way, you know exactly what you've got. Nothing will drive you crazy faster than spending an hour troubleshooting a test and then find it was that damn, cheap cable!
Ed
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