PRO2004.11

     The  PRO-2004 contains  a  "window  detector"  circuit,
     which  is  called  into play during a SEARCH operation.
     This circuit tries to detect when the  radio  is  tuned
     close  to  the  center  frequency  of  a  station,  and
     prevents the search from halting  prematurely,  off  to
     the side of the signal.

     The AFC (automatic frequency control)  circuit  of  the
     Bearcat 800XLT often causes a search of 850 MHz signals
     to halt prematurely.  Even though the signal sounds  on
     frequency,  the display reads the wrong frequency.  The
     PRO-2004 does not have this problem.

     Another interesting feature is the SOUND SQUELCH, which
     may be used during scan or search operations.  With the
     the sound squelch enabled,  signified  by  a  red  lamp
     above  the pushbutton, the scanner will skip over unmo-
     dulated signals.  This is handy for skipping over "bir-
     dies", or link signals with a constant carrier.

     According to the owner's manual:

        -  "When the PRO-2004 stops at a frequency which has
          no  sound,  it  remains there for 0.5 seconds, and
          then goes to the next frequency if"  no  sound  is
          detected "within that time."

           "When  a  frequency  which  contains   sound   is
          received, it halts at the frequency.  But,

            a.  If the sound ceases during the reception, it
                stays  on  the  frequency for 5 seconds, and
                resumes scanning."

            b.   "If the [station] stops sending a  carrier,
                the unit reverts to scan [or search] immedi-
                ately if DELAY is off, after 2  seconds,  if
                the DELAY is active."

     The manual warns that the sound squelch may  be  fooled
     by  signals  with  low  modulation, and skip over them.
     The PRO-2004 SOUND SQUELCH tries to detect the presence
     or  absence of modulation (not human speech), so unfor-
     tunately, it thinks that mobile phone idle tones, digi-
     tal data signals, and paging tones are worth monitoring
     and will stop the scanner to listen to them.