R7000.21

     In the  past  month,  several  Kenwood  SM-220  monitor
     scope/panadaptors  have appeared at hamfests selling in
     the $200 to $250 range.  The Kenwood SM-220 can display
     transmitted  or  received  signals.   To  add  spectral
     display capability to the SM-220, one must purchase the
     optional  BS-5 or BS-8 module, which consist of a prin-
     ted circuit board, a steel  enclosure,  interconnecting
     cables,  and  a  new  graticule.  The panadaptor module
     mounts inside the SM-220 cabinet.

     The BS-5 is used with the TS520 and TS530 transceivers,
     which  have  an IF of 3.395 MHz.  The BS-8 is used with
     the TS820 and TS830 transceivers, which have an  IF  of
     8.830 MHz.  Since the IF of the ICOM R7000 is 10.7 MHz,
     one must alter the panadaptor circuitry to accept  10.7
     MHz input.

     If you have any choice in the matter, get the BS-8,  as
     it  requires  fewer changes than the BS-5, and may even
     require no changes at all!

     The  panadaptor  module  circuit  consists  of  several
     stages,  but  only  two  are directly related to the IF
     frequency:

       1.  A crystal oscillator is used as a marker  genera-
           tor.

       2.  A voltage tuned oscillator is swept across the IF
           of  the receiver, and employs a varicap diode, an
           inductor and capacitors.

     The marker generator is not vital for panadaptor opera-
     tion.   It  merely provides a single "pip" that one may
     use to center the display on the  CRT  screen,  and  is
     similar  in  purpose to the crystal calibrator in older
     receivers.

     The marker generator circuits in the BS-5 and BS-8  are
     identical  except  for  one  crystal.   One  need  only
     replace the 3.395 MHz crystal (in the BS-5),  or  8.830
     MHz  crystal  (in  the BS-8) with a 10.7 MHz crystal to
     adapt the SM-220 marker to 10.7  MHz  IF.   I  did  not
     alter  this stage, although I would if I had a 10.7 MHz
     crystal handy.

     The voltage tuned oscillator is the stage that deserves
     our  attention.  The changes required depend on whether
     you have the BS-5 or BS-8 panadaptor module.


                     Changes for BS-5 Module

     Change the following capacitors:

       1.  C231 from 1000 pf to 68 pf.

       2.  C232 from .01 uf to 1000 pf.  (You  can  use  the
           capacitor which used to be C231.)

       3.  C234 from 100 pf to 22 pf.

       4.  C236 from 47 pf to 22 pf.

       5.  C237 from 680 pf to 100  pf.  (You  can  use  the
           capacitor which used to be C234.)

     Solder a 10 microhenry inductor in parallel with  L204,
     a 20 microhenry inductor.