Posted for "Chatfield S. Daniel" <csdaniel@FNBSouth.com>:

 Paul,
 Does the Garmin 430 have an internal diplexer?
 Chat Daniel

""
  Did you use a dilexer or a power splitter to tie the two SL30s to the
  antenna? A diplexer seperates the GS and VOR band signals. The SL30
 has an
  internal diplexer, which is why there is a single antenna input. If
 you use
  an external diplexer and connect the "VOR" output to the SL30 antenna
 input
  you are starving one SL30 for GS signals and the other for VOR
 signals. All
  that is getting through is what leaks past the diplexer, probably
 15-20 dB
  down from the signal the antenna is capturing. A simple VHF/UHF power
  splitter should be used rather than a diplexer.
""