I am a little confused...does a leader using a radio cause loss of concealment? I hear conflicting answers to this question. I think it does as it is use of a support weapon.
As per the Concealment Gain/Loss Table case C, an infantry unit loses concealment if:
C If it engages in any other action [EXC: using a radio/field phone; Spotting; taking a PAATC (and Leader DRM applied to such a PAATC) not caused by a vehicle entering its Location; SW/Gun repair attempts, dropping SW; taking a Set DC NTC ];
I don't think the leader is even dmarked with a Prep Fire counter. Right?
1.2 RADIO CONTACT ATTEMPT: ...Only an Observer (i.e., a Good Order leader possessing a functioning radio/field-phone counter [1.6], or an OP tank [H1.46], or an Offboard Observer [1.63; E7.6]) may attempt Radio Contact [EXC: not if he is a Rider, or a Guard whose US# is < that of his prisoners], and may do so only at the start of the PFPh/DFPh (as given in the Advanced Sequence of Play) as his sole action for that phase aside from other allowed OBA activities. ...
The rule doesn't even mention the use of the Prep Fire Counter. It's done in the PFPh/DFPh. Of course, if the leader is HIP you can't mark it as prep fired...
C1.6:
"An Observer who uses a radio (including any unsuccessful attempt to make or maintain Contact) may attempt no actions other than OBA direction during that PFPh (and may not move in the following MPh) or DFPh and if not hidden/concealed is marked with a Prep or Final Fire counter, but does not lose any “?” he may have."
See Chapter C note 5 on page C23 of the RB. You may find many players have the radio/fld phn off map and recorded on a side note to the SMC who is the observer. This avoids the often obvious location from drawing every point of FP to break the concealed stack. Since a SMC w/ radio/fld phn can still do other actions in the rally phase (and some others) it makes the observer less obvious.