I've been working with a passive DAS system deployed on Meru. I am interested in gaining a better conceptual understanding of all the RF factors that might come into play here and hoped you all could help explore the topic.
A typical system block looks like this:
- Two Meru AP310s (single radio a/b/g/n) mounted next to one another in an IDF. One port is attached to the DAS, the other two ports have 50-ohm terminators. Apparently, the capped ports can not be disabled, so all three ports are transmitting at 20dBm.
- The coax heads into a passive RF splitter with 3.5dB insertion loss (including splitting the signal) and a VSWR of 1.4:1. The two split ports each go into another splitter. These four ports go to 2dBi omni antennas.
- I don't know the cable specifics at this time or average run length. I am just averaging 3dB loss for now.
I'm guessing this leaves a little under 12dBm being radiated from the antennas.
So, I'm left with at least a few puzzling questions at the moment:
- Is there a chance the APs will successfully receive a client transmission on the capped ports if the client is located near the closet (in other words, closer to the AP than the antenna) and then try to transmit on the same port? How much energy is typically absorbed by a terminator?
- Since the APs are operating on the same channel and are mounted side-by-side, how much might they affect one another?
- Are there any other issues that might arise from connecting multiple splitters in series due to the cumulative VSWR?
I guess the net affect is a lowering of overall system capacity. Any further thoughts you all have on this are appreciated! As someone mentioned in an earlier post about the toughest thing to learn for the test, I'd agree that it is the RF portion.