92 lines
4.5 KiB
Plaintext
92 lines
4.5 KiB
Plaintext
|
||
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
|
||
PK-232s.
|
||
|
||
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
|
||
follows:
|
||
|
||
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
|
||
|
||
|