The only antenna value that SERIOUSLY affects range, in most cases, is antenna height.
If you're not line of sight, the signal goes away completely. No amount of preamps, high gain antennas, or good coax will compensate for 'no signal'.
A 5 watt handietalkie can talk to another 5 watt handietalkie 200 miles away... if one of them is on the space shuttle, and thus, in direct line of sight. And that with pretty poor antenna, too!
Gain antennas can help with signals that are present, but weak. They can also sometimes help you find a reflection of the desired signal from something not in the expected direction, but up high.
But your actual expected range is 95% or more purely due to height of the transmitting antenna, height of your antenna, and lack of hills/trees/buildings in between that block line of sight.
Sometimes atmospheric conditions can cause signals to 'bend' a bit (tropospheric ducting) and can cause VHF signals to travel hundreds of miles. But you can't count on it, day to day.
In most city areas, you'll get more 'help' from adding an FM Broadcast trap to the antenna line than you will from changing to a 'gain' antenna, and thus reducing the front end overload FM broadcasters tend to cause to scanners in any major city.
This doesn't say a 'good' antenna can't help... but it isn't magic, it won't give you a signal where there isn't one to be had. Probably the only area of listening where a good gain antenna (of the proper circular polarization) is especially needed is monitoring military UHF satellites, as they are very weak signals, even though they ARE 'line of sight'.
Your wireless mike in particular, might benefit some from a gain antenna. However, the MOST you can expect is double the range, to 1 mile, for 6 db gain over current. Wireless mikes are intended for no more than 100 foot range, if operated legally. They are very low power, with poor antennas at best. The discone is probably not very good for receiving it, though. Given the low height of the wireless mike antenna, most of your problem is probably buildings and trees between you and the mike, which will degrade the signal badly.
) is it possible to equate antenna gain with distance a signal can be received. For instance I want to build a 4 element J-Beam antenna and I should get about 6 dBd gain. I have a signal (wireless mike) that I can pick up about 1/2 mile away. My question is how much farther can I pick up the wireless mike based on 6 dBd of gain? I am trying to decide if building the antenna would be a waste of time. I plan to put it on a rotor. I am currently using a discone antenna.--Gary
