Recently, several new packeteers using PK-232s have appeared
on  our local duplex repeater which is dedicated  to  packet
radio.    This   is  one  environment  where  the  collision
frequency  should  be  very low since there  are  no  hidden
terminals.  Almost immediately we noticed that the collision
frequency had risen dramatically.   After some investigation
we discovered certain stations were almost guaranteed to  be
involved in stepping on in-progress packets.  These stations
were  contacted and in all but 1 case they were new users of

We were very puzzled as there have always been some stations
on  the  repeater using PK-232s with no  apparent  problems.  
The new stations were asked how their station was configured
and what method was used to get the DCD operation  adjusted.  
We were very surprised at the answers we got.   Every single
one  of  the  offending stations had set  their  station  up
exactly  according to the instructions in the PK-232 manual.  
However, contrary to the advice given in the manual, none of
these stations had configured their setup so that they could
hear  what was going on on the channel when the  PK-232  was
connected  to the radio.   None of these new operators  knew
what DCD meant, what it did, or why it was important that it
should be working on a multiple access packet channel.

We  obtained  a PK-232 and manual to try  and  discover  the
exact  nature  of  the  problem.   What we  found  was  that
although  the  manual is very complete  and  generally  very  
well written, there are some areas where it leaves something
to be desired.  Specifically, in this case, the instructions
given  on page 2-16 (we had manual PK232UG Rev.  B 9/86  for
reference) for setting up the PK-232 and an FM radio for DCD
operation  are  simply  incorrect.   If set  up  exactly  as
described,  DCD  will  NEVER  be asserted  during  a  packet
transmission  by  another station on the channel!!   We  had
found the cause of our problem.

If  you  have a PK-232 and haven't already  discovered  this
problem for yourself,  please disregard the instructions  in
the  manual for setting up a PK-232 and NBFM radio for  1200
baud  packet  operation and use the method  presented  here.  
All your packet neighbors will appreciate it very much.

The manual is quite corect in all respects EXCEPT where they
discuss setting the DCD THRESHOLD control and receiver audio
output   level  for  proper  demodulation  and  DCD  circuit
operation.   The correct way to set these adjustments is  as

     1.  At  least temporarily,  arrange to be able to  hear
         the  receiver audio signal which is being  sent  to
         the PK-232.

     2.  Set  the  squelch circuit on the radio  for  normal
         squelched operation.  The DCD circuit in the PK-232
         is  incapable of proper operation with  unsquelched
         audio from the receiver.

     3.  While  monitoring  incoming  packets,   adjust  the
         receiver  audio level so that the tuning  indicator
         "spreads"  fully when receiving a packet  from  the
         station  on  the channel which produces  the  LEAST
         amount  of audio output level.   There are  several
         limiters   in  the  PK-232  demodulator  so  louder
         stations will not be affected adversely by this.

     4.  Once  the audio level is properly set,  adjust  the
         DCD THRESHOLD control on the PK-232 so that the DCD
         led lights when there is a packet being transmitted
         by the station on channel which produces the  LEAST
         amount  of  audio output from the  receiver.   Make
         sure,  however,  that  the DCD LED is  extinguished
         when  there  is no signal and the  radio's  squelch
         circuit has cut off all audio from the receiver.

If the above procedure is followed, the PK-232 will properly
hold  off  transmitting  during a packet  transmission  from
another  station  and  will  not  send  acknowledgements  to
individual frames of a maxframe greater than 1 packet  while
it is still being transmitted.

We  hope PK-232 owners will find this information useful and
take  steps to assure that their DCD is operating  properly.  
Multiple  access  packet  channel  throughput  is   severely
degraded when DCD is not working.

73 and happy packeting,

Eric Gustafson  N7CL

GW1NGL NA7KR Kevin Roberts Ham Radio

Page last updated on 09/10/2012 by Kevin Roberts NA7KR a colection of Ham Radio and Electronic Information