I cannot understand why I can receive a very strong signal from a foreign country & not be able to communicate on the same frequency. Thank you.
We assume your question is in regard to 40 meters and the differing allocations between ITU Regions 1, 2, 3 ??
This Wikipedia entry is not complete, but provides how the differences began (BTW, WW2 was a factor).http://en.wikipedia.org/wiki/40-meter_band
Only since 2009, have international communications (split) been possible --- foreign country SW stations still exist in the 40 / 41 meter allocation.