92 lines
4.5 KiB
Plaintext
92 lines
4.5 KiB
Plaintext
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Recently, several new packeteers using PK-232s have appeared
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on our local duplex repeater which is dedicated to packet
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radio. This is one environment where the collision
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frequency should be very low since there are no hidden
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terminals. Almost immediately we noticed that the collision
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frequency had risen dramatically. After some investigation
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we discovered certain stations were almost guaranteed to be
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involved in stepping on in-progress packets. These stations
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were contacted and in all but 1 case they were new users of
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PK-232s.
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We were very puzzled as there have always been some stations
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on the repeater using PK-232s with no apparent problems.
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The new stations were asked how their station was configured
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and what method was used to get the DCD operation adjusted.
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We were very surprised at the answers we got. Every single
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one of the offending stations had set their station up
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exactly according to the instructions in the PK-232 manual.
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However, contrary to the advice given in the manual, none of
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these stations had configured their setup so that they could
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hear what was going on on the channel when the PK-232 was
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connected to the radio. None of these new operators knew
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what DCD meant, what it did, or why it was important that it
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should be working on a multiple access packet channel.
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We obtained a PK-232 and manual to try and discover the
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exact nature of the problem. What we found was that
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although the manual is very complete and generally very
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well written, there are some areas where it leaves something
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to be desired. Specifically, in this case, the instructions
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given on page 2-16 (we had manual PK232UG Rev. B 9/86 for
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reference) for setting up the PK-232 and an FM radio for DCD
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operation are simply incorrect. If set up exactly as
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described, DCD will NEVER be asserted during a packet
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transmission by another station on the channel!! We had
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found the cause of our problem.
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If you have a PK-232 and haven't already discovered this
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problem for yourself, please disregard the instructions in
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the manual for setting up a PK-232 and NBFM radio for 1200
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baud packet operation and use the method presented here.
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All your packet neighbors will appreciate it very much.
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The manual is quite corect in all respects EXCEPT where they
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discuss setting the DCD THRESHOLD control and receiver audio
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output level for proper demodulation and DCD circuit
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operation. The correct way to set these adjustments is as
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follows:
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1. At least temporarily, arrange to be able to hear
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the receiver audio signal which is being sent to
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the PK-232.
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2. Set the squelch circuit on the radio for normal
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squelched operation. The DCD circuit in the PK-232
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is incapable of proper operation with unsquelched
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audio from the receiver.
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3. While monitoring incoming packets, adjust the
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receiver audio level so that the tuning indicator
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"spreads" fully when receiving a packet from the
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station on the channel which produces the LEAST
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amount of audio output level. There are several
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limiters in the PK-232 demodulator so louder
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stations will not be affected adversely by this.
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4. Once the audio level is properly set, adjust the
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DCD THRESHOLD control on the PK-232 so that the DCD
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led lights when there is a packet being transmitted
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by the station on channel which produces the LEAST
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amount of audio output from the receiver. Make
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sure, however, that the DCD LED is extinguished
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when there is no signal and the radio's squelch
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circuit has cut off all audio from the receiver.
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If the above procedure is followed, the PK-232 will properly
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hold off transmitting during a packet transmission from
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another station and will not send acknowledgements to
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individual frames of a maxframe greater than 1 packet while
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it is still being transmitted.
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We hope PK-232 owners will find this information useful and
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take steps to assure that their DCD is operating properly.
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Multiple access packet channel throughput is severely
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degraded when DCD is not working.
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73 and happy packeting,
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Eric Gustafson N7CL
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