Both maximum transmission distance and coverage depend on the magnetic field pattern for Wi-Fi signal of an antenna.
Omni-directional antennas are used when the coverage required is in all directions around the horizontal axis of the antenna. Omni-directional antennas are most effective where large coverage areas are needed around a centre point. For example, placing an omni-directional antenna in the middle of a large, open room would provide a good coverage. Omni-directional antennas are commonly used for point-to-multipoint designs with a star topology.
Semi-directional antennas are ideally suited for short and medium range bridging. For example, two office buildings that are across the street from one another and need to share a network connection would be a good scenario in which to implement semi-directional antennas. In a large indoor space, if the transmitter must be located in a corner or at the end of a building, a corridor, or a large room, a semi-directional antenna would be a good choice to provide the proper coverage.High-gain antennas do not have a coverage area that client devices can use. These antennas are used for point-to-point communication links, and can transmit at distances up to 20 Km. Potential uses of highly directional antennas might be to connect two buildings that are miles away from each other and have no line of sight obstructions between them.

Theoretically, there is no limit on the maximum number of user that can access AP. However, the maximum data transmission rate available is 54Mbps according to IEEE 802.11a/g. The more users connected to the AP, the smaller bandwidth each user can have.
We have tested our AP with 20 users per interface (one interface for 500AG and 2 interfaces for 600AG), and have data rate around 2Mbps.

There are a few possible causes for this lost ping problem:
1.Do make sure there is no duplicate IP address in the system. When there is another device using the same IP as the AP, then the system cannot decide which one to ping and result in lost ping.

Aphelion AP operating in 802.11a mode has maximum transmission power of 17dBm and in 802.11b/g has maximum transmission power of 18dBm.
We also have Aphelion high power series AP available soon. This high power series AP offers 20dBm in 802.11a mode and 24dBm in 802.11b/g mode. Please refer to product specifications for more detail.

Aphelion outdoor AP has waterproof housing with highest sealing protection IP68 certified. As long as the connectors of power cord and antenna RF cable are properly installed with self-bonding insulating tape wrapped. AP can operate normally even in extreme weather.
The environmental specification of Aphelion AP is
Operation temperature :
-30^oC ~ 60^oC,
-40^oC ~ 60^oC with heating element installed (optional)
Storage : 40^oC ~ 80^oC.