A good grade of RG58 will lose half your signal (3db) when the line is 100 feet long. A cheap grade, of which there are far too many, will lose a bit more, and the loss gets much greater as you go higher in frequency. It pays to use the least lossy coax you can afford, especially is you're doing 800/900 mHz monitoring. All the reputable manufacturers publish the loss of their cable in terms of db per 100 feet, so do some research online and you'll come up with something you can afford which does the job for you. You'll also want to stick with cable that has a MANUFACTURER'S name on it, not a reseller or dealer.