R7000.9

        MODIFY YOUR ICOM R7000 TO SCAN AND SEARCH FASTER

                      by Bob Parnass, AJ9S

     This article describes how to  increase  the  scan  and
     search speeds of the ICOM R7000 receiver by 60% without
     noticeable performance degradation.

                           Background

     The  front  panel  SCAN  SPEED  control  on  the  R7000
     receiver  allows  the user to adjust the speed of scan-
     ning and searching operations, as well as the  rate  at
     which  the  priority  channel is sampled.  Rotating the
     control counterclockwise decreases the speed, and rota-
     ting it clockwise increases the speed.

     When the SCAN SPEED control on my R7000 (serial  number
     001400)  was  turned  fully  clockwise, the radio would
     scan a maximum of about 8  channels/second,  or  search
     about  8  increments/second.   As  the  following table
     shows, the stock R7000 can scan  about  as  fast  as  a
     Radio Shack PRO-30 or PRO-2003.

     TABLE 1.  Maximum Scan Rates of Selected Receivers

      _____________________________________________________
     |             Scanner               Maximum Scan Rate|
     |                                |  (channels/second)|
     |________________________________|___________________|
     | Kenwood TR-2600                |         1.2       |
     | Radio Shack PRO-30             |         8         |
     | Radio Shack PRO-2003           |         8         |
     | ICOM R7000 (stock)             |         8         |
     | ICOM R7000 (after modification)|        13         |
     | Regency M400                   |        13         |
     | Bearcat 20/20                  |        15         |
     | Bearcat 300                    |        15         |
     |________________________________|___________________|



                       R7000 Scan Circuits

     The scan rate of the R7000 is determined, in part, by a
     simple  clock  outside  the  microprocessor.  The front
     panel SCAN SPEED rheostat and resistor R18  (and  other
     components in the LOGIC UNIT) control the speed of this
     clock.  The clock output is connected to  what  appears
     to  be an input port on the microprocessor.  The upshot
     is that we can affect the scan rate  without  affecting
     the other chores performed by the microprocessor.

     The modification consists simply of soldering a 470,000
     ohm  resistor  across  the leads of resistor R18 on the
     LOGIC UNIT circuit board.
CONTINUED IN R7000.10