using two antennas
I've got an in-door WiMax modem for the internet, it came with 2 detachable small antennas but the signal was weak. My friend advised me to get an Out-door directional antenna from the market and connect it by RG58 cable to my WiMax device. I bought two 14DBi antennas and installed them on the wall from outside pointing to the transmitters then used two 1.5 Meter RG58 cables to the WiMax modem. After doing that I got an acceptable change in the signal as I got higher SINR reading so I tried on the roof of the building and I got even very much better signal but the problem if I want to install them on the roof, then I need 25 meters of RG58 cable to connect it to my indoor wimax modem which will lose all the 14 DBi.
I heard that I can use the two antennas as one to increase the gain so I can use one long cable only to my WiMax modem. Is that possible ?
Thank in Advance
Two or more antennas placed at particular distance between them and phased properly can increase the gain of the system.
Check the net about Phasing Antennas.
Two antennas at best can give 3dB gain only.
It will not be sufficient to compensate loss however you can try
Hmmmm, What about amplifier .... like this one http://www.gps-repeating.com/product...er_gpsr-a.html
There are a number of issues to consider. Combining antennas can increase the gain and you generally get a 3 dB increase, or a bit more if you do it correctly. You can also hurt the situation if you make an error. You are probably bette off with a single antenna.
You might want to consider other lower loss coax options. Generally the bigger the coax diameter, the lower the loss (and the higher the cost).
An amplifier immediately after an antenna can help overcome cable loss but again you have to pay attention to the details. It is probably a good idea to add a bandpass filter in front of your amplifier to reduce the chance of saturating your amplifier with nearby but out of band signals. Look into LNA's (low noise amplifiers).
Amplifier noise figure, gain linearity, third order intercept, power consumption, cost etc. are additional factors to consider.
Various trades are more easily understood if you do a "link budget" analysis.