I am using Xbee S1 also and the configuration is setup similar to yours.
From Digi's website, the datasheet for XbeeS1 clearly states that it can go upto 30m indoors but I can hardly get 10meters. Outdooe LOS the same story...
Is there any way to use external SMA antenna to boost this or is this all that I have to live with ?
If that isnt the reason, it may be due to there not being enough power supplied to the modules/board, malfunctioning xbee module, non-compatible antenna, environmental density etc.
Goodluck
Despite the royal claims, in my experience, 10m is about the normal "indoor" range for XBee
modules, which have only 1 mW transmit power. For better range, get the 50 mW XBee Pro
modules, which I found to have effective outdoor LOS range of about 100m, and enough indoor
range to get around the entire house. Also, the pcb antennas are inferior to the 1/4 wave
whip and dipole antennas, so forget pcb if you want range.