With reference to the cable we did following:The exsiting cable is already 5m long. We tested the VHF/GPS combination antenna with an additional 10 m long cable. At the end the total cable length was 15 m. The additional cable was a simple RG58 cable. It had a male TNC plug and a female TNC plug as extension plugs between the existing cable and the TRX. The plugs were crimped to the cable. This worked very well. All the satellites in our hemisphere were visible.
Therefore we can guarantee a 100% working for a cable length of 15m with RG 58. But as you know as better the cable is, as better the reception and transmission will work.