Using RG-58 at 800 MHz over a 17 foot run is losing almost half your signal. 2.45dB to be exact. If you were using this for transmitting (I know, you aren't, but just for example) if you put 100 watts in at one end, you'd get about 54 watts out of the other end at 860MHz. The other 46 watts are lost in the cable, converted to heat and never make it to the other end.
On the other hand, if you use RG-6:
1.5dB of loss at 800MHz, or if you put 100 watts in, you'd get about 70 watts out the other end.
RG-58 is used in mobile installations because it's small, flexible and cheap. In a base installation, you'd really want to use something better if you can, especially if you need more than the few feet of cable you have.
While you were at it, I'd say get a real base antenna, it'll likely last longer and work a bit better. But, budgets are budgets, and we do the best with what we can afford.