
[ ANARTS - Australian National Amateur Radio Teletype Society ]

ANARTS RTTY NEWS BULLETIN 809  15 May 1994

Sunday Transmission Schedules.
  3.545 MHz (Plus/minus 3)   0930 UTC     VK2BQS (Jim)
  7.045 MHz (minus 3)        0030 UTC     VK2CTD (Col)
 14.070 MHz (amtor/fec)      0030 UTC     VK2DPM (Alan)
 14.091 MHz                  0030 UTC     VK2BQS (JIM)
146.675 MHz             0030/0930 UTC     VK2JPA (PAT)
144.850 MHz (ax25 bbs)                    VK2JPA AT VK2RWI
146.675 MHz (rtty mmbbs/repeater)          VK2RTY

Views  expressed  in  this news bulletin are  not  necessarily
those of the Broadcast Officer, the Relay Officers,  or of the
Society.


G-TOR - An Improvement?

G-TOR  is  a new digital mode,  which has  been  developed  by
Kantronics.  Most  of its features (like on-line Huffman  data
compression,  link-quality  based baud rate  adjustment,  CRC,
fundamentals  of the packet structure,  etc.) are adopted from
PACTOR.  The  baud rate used in G-TOR can be 100,  200 or  300
baud.  The main differences are the use of Golay forward error
correction coding with the obligatory data interleaving and  a
hybrid ARQ system.

The Golay encoding however, as used in the G-TOR mode, is only
able  to correct 3 bits in a block of 24 bits and only half of
this  block (12 bits) carries information.  The  remaining  12
bits have to contain the required redundancy, and no new data.
It  is therefore only possible to correct a few errors despite
the large overhead.  For this reason the Golay encoding  would
only be useful for errors caused by short spikes on the higher
short wave frequencies (10 to 20m).

You cannot  however expect it to provide any  improvements  in
typical  80m conditions.  Here it is necessary not only to use
hybrid-2 ARQ systems, but also suitable, powerful (invertible)
codes,   which  allow  the  reconstruction  of  the   original
information,  even  when only the redundany block is received,
rather than Golay or similar simple blockcoding,  which always
requires  both  blocks to be received to get the  data  trans-
ferred.

The   most  robust  HF  (short  wave),   narrow   band,   data
transmission systems known,  apply very powerful convolutional
codes  with Viterbi decoding and soft decision  (requiring  an
ADC/DSP just like analog Memory-ARQ).  The processing speed of
those  systems exceeds the capability of a KAM by factor  100.
Despite this very expensive approach, they only achieve around
10 dB better weak signal performance than PACTOR-1. The closer
a system approaches the Shannon boundary (theoretical through-
put  limit) the more difficult it gets to gain another one  or
two decibels.


W0XI  et  al claim that they were able to transfer  a  certain
file  on the 20m band in about 5 minutes using G-TOR,  whereas
PACTOR,  which was used afterwards, took about 20 minutes. The
conclusion  was that G-TOR would be about 4 times faster  than
PACTOR in general, which is actually impossible!! According to
the system description, G-TOR can on average only be about 1.5
times faster than PACTOR.

The 20m band,  which was used for the tests, normally provides
a  good SNR and only very few fluctuations.  It  is  therefore
obviously  no problem to reach higher throughputs,  especially
when  using 300 baud (even short wave Packet Radio could  have
been faster than PACTOR in this case).  Also,  the  comparison
between  PACTOR  and  G-TOR  was based on  the  PACTOR  imple-
mentation in the KAM,  which does not, apparently, provide the
full  performance anyway,  due to the different converter  and
the missing ADC.  Since the KAM already uses a modem  designed
for 300 baud operation,  it is obvious that G-TOR is favoured.

The  original PACTOR system will still do better than G-TOR on
weak signals, as an ADC is used in the PACTOR-Controller (PTC)
to allow real analog Memory-ARQ. To achieve impartial results,
you have to transfer the same files containing random  charac-
ters on the typical 80m conditions in G-TOR using two KAMs and
in  PACTOR  using two PTCs.  

The  8.64 characters per second,  considered to be the typical
average throughput of PACTOR,  and which led to the conclusion
that  G-TOR  would be 4 times faster  than  PACTOR,  are  much
slower than the average rate we obtained with our units. Under
even  worse  conditions we obtained around 17  characters  per
second,  depending  on the transferred information due to  the
Huffman coding.

Regardless of the Huffman data compression, which improves the
throughput of both systems in the same way,  the comparison of
throughput  between PACTOR and G-TOR can be easily calculated.
According to the protocol description published by W0XI, G-TOR
is able to transfer a maximum of 19 characters per second when
running  on  200  baud (They claim 69 data bytes  in  a  cycle
duration  of  2.4 seconds at 300  baud,  which  means  maximum
2/3*69/2.4  characters  per second at 200 baud).  The  maximum
rate of PACTOR at the same speed is 16 chrs/s,  which is a re-
lationship  of 1.18 to 1.  The Golay encoding is not  able  to
improve the throughput so dramatically that you finally result
in  a factor 4.  It must be remembered that the analog Memory-
ARQ, as used in the original PACTOR implementation, is able to
improve the effective signal-noise ratio with each  aggregated
packet  and  hence enables a higher throughput (especially  in
weak conditions) than the Golay coding gain.  It is  therefore
obvious  that the higher maximum throughput of G-TOR is mainly
based on its higher maximum baudrate.  This however means,  it
has to exceed the usual 500 Hz band width limit.

With  this  in mind it must also be remembered  that  a  wider
receiver  bandwidth  receives  more noise.  A 300  baud  G-TOR
signal will therefore have a poorer S/N ratio than a 200  baud
PACTOR  signal (if they are both of the same fieldstrength and
the receiver bandwidth is correctly adjusted for both  modes).
As  signals decrease,  G-TOR would have to switch to 200  baud
before  the  PACTOR  signal would be  affected,  thus  further
reducing some of the proposed speed gain.

There are still some more disadvantages of G-TOR in comparison
to  PACTOR,  e.g.  the  cycle duration is quite  long  at  2.4
seconds,  and will increase to almost 5 seconds when using the
Golay  encoding,  hence leading to quite long break-in  times.
The  speed adaptation times are necessarily also longer,  thus
leading  to  poorer  results in  rapidly  changing  conditions
(multipath).

Furthermore,  the interleaving and the 3 different baud  rates
used in G-TOR will probably lead to a lot of problems with the
listen mode,  an important point for all digital modes used in
Amateur Radio.

Actually G-TOR is just a modified PACTOR system, which probab-
ly  does not provide enough improvement that introducing  this
mode as another new standard would be worthwhile.  With regard
to  the basic requirements of each digital data transfer  mode
(like throughput,  bandwidth, error rate, etc.) PACTOR already
represents  nearly the optimum attributes that are  obtainable
with an FSK system. A real improvement over the current PACTOR
system  can  only be reached when using  different  modulation
schemes like PSK,  which require a DSP hardware.This step will
be done this year with the introduction of PACTOR Level-II.

Tom Rink, DL2FAK
          -----------------------------------------

VOLTA RTTY WW Contest (conclusion) 

Contest period: from 1200z Saturday to 1200Z Sunday 14-15 May
                (24 hours, no rest periods required)

Final score = total QSO points x total mults (band mults  plus
each  INTERNATIONAL COUNTRY worked on 4 bands) x total  number
of QSOs. Use exchange points table to determine points  scored
for each QSO.

Awards:  A  SPECIAL trophy will be awarded to the top stations
in each class. In addition, a certificate with special sticker
to all entrants.

Logs:  Use separate logsheets for each band.  Logs must  show:
BAND,  DATE  and  TIME (UTC),  CALLSIGN and MESSAGE  Sent  and
Received, POINTS and NEW MULTIPLIER PREFIX. Summary sheet must
show full scoring, and list of multipliers worked.

Logsheets,  summary  sheets amd multipliers and dupesheets and
the  EXCHANGE POINTS TABLE are all available for copying  from
the RTTY Contesters Guide, published by RTTY Journal.

Logs must be received by July 30, 1993, to qualify.

Mail logs to:
   Francesco Di Michele, I2DMI
   P.O. Box 55
   22063 Cantu
   Italy
          -----------------------------------------

                      IPS weekly report
                      -----------------

                       6 May - 12 May 1994
Issue No 19
Date of issue: 13 May 1994
INDICES:
Date     06    07    08    09    10    11    12
10cm    074   074   074   077   080   082   087
A        29    30    33    24    24    25  (11 estimated)
T        13    17    10   -10    11    22    15

              I.P.S.  SUMMARY OF ACTIVITY

Solar activity was very low during the period.

The  geomagnetic field at Learmonth (WA) was mostly  unsettled
to active. There were minor storm periods on 7th-8th, and 11th
May

Ionospheric  F2 critical frequencies at Sydney were  about  10
per  cent  below  predicted levels on  6th,  and  mostly  near
predicted   values  for  the  rest of  the  week.  There  were
depressed periods to 30 per cent on 8th, and to 40 per cent on
11th.  Spread F was reported on 6th-9th,  and 11th-12th,  with
Sporadic E observed on 11th May.

           FORECAST FOR THE NEXT WEEK (13 - 19 May)

SOLAR:        Very low to low

GEOMAGNETIC:  Mostly  quiet to unsettled today.  Unsettled  to
              active with minor storm levels  14th-15th.

IONOSPHERIC  Near predicted monthly values to 30 per cent down
             14th-15th.   Otherwise  near  predicted   monthly
             values. Spread F may degarde night communications

Courtesy of IPS Radio and Space Services
           ----------------------------------------

VK2SG RTTY DX NOTES 6 MAY 94

VK2SG RTTY DX NOTES FOR WEEKENDING 6 MAY 1994  (BID RTDX0506)

OUR THANKS THIS WEEK GO TO ZS5S, I5FLN, I5ICY, IK5AAX, J28JJ,
WB2CJL,  DJ3IW  AND THE CENTRAL EUROPE DX CLUSTER DB0SPC, AND
THE NJ0M NODE OF THE TWIN CITIES DX PACKETCLUSTER NETWORK.

BANDPASS:
FRIDAY 29
0550-14083 C91AI
0910-14087 T92X
1703-14084 VS6GA QSL KG6GA
2155-14087 5T5MS

SATURDAY 30
0723-14084 WL7EF
1026-14088 T28RW QSL ZL1AMO
1102-14088 YT7OX
1214-14087 S51DX
1214-14087 KG4CC
1544-14085 XU7VK
1726-14084 BV7WB
1845-14086 VY2SS
1944-14083 UA6JBQ
2237-14085 9A3TB

SUNDAY 1
0703-14085 5B4VX
0711-14087 NH6XM
0741-14081 YT7OX
0744-14086 NL7VJ
1029-21086 Z21HD
1415-21085 VS6GA
1425-21070 J28JJ ARQ
1428-14088 HL1XP
1443-21084 ZD7DP
1556-21085 A41KD
1609-21080 TZ6FIC
1656-21083 VP8CIL
1728-14092 VY2SS
1730-14088 YT7CC
1922-21085 ZP5YW
1923-21086 FG5FI

MONDAY 2
0550-14082 C91AI

TUESDAY 3
NO REPORTS

WEDNESDAY 4
NO REPORTS

THURSDAY 5
NO REPORTS

NOTES OF INTEREST:

NORTHERN MARIANAS - JA6VZB AND JF6BCC WILL BE QRV FROM 26-30 MAY FROM KH0,
FOR THE CQ WPX CONTEST. OUTSIDE OF THE CONTEST THEY WILL BE QRV ON RTTY.
QSL KH2GR/KH0 TO JF6BCC AND AH0T TO JA6BSM.

CRETE -JULIUS, HA6NY, WILL BE ACTIVE AS SV9/HA6NY FROM 24-31 MAY ON RTTY

80 TO 10 METERS.

MARKET REEF - A GROUP CONSISTING OF OJ0/AC6T, OJ0/OH1VR, OJ0/OH6RM,
OH0MB, AND OJ0/OH2BBF WILL BE ACTIVE 14-17 MAY ON SSB, RTTY AND CW.
QSL TO HOME CALLS, EXCEPT OH0MB  WHICH SHOULD BE QSL'D TO OH0RJ.

BARBADOS -8P9GQ WILL BE ACTIVE ON CW, SSB AND RTTY 10-30 MAY, 80 TO 10 METERS.

ITU GENEVA - NOW UNTIL 11 MAY 4U9ITU ON CW, SSB AND RTTY. ALSO FROM
20-22 MAY A GROUP OF ITALIAN OPERATORS WILL BE ACTIVE USING THE SAME CALLSIGN

SEND YOUR BANDPASS AND NOTES OF INTEREST FOR NEXT WEEK'S BULLETIN TO
LUCIANO I5FLN AT ZS5S.ZAF.AF OR AT I5FLN.ITA.EU.

73 AND GOOD HUNTING DE JULES W2JGR AT W2TKU.#SRQFL.FL.NA

(VIA HF CLOVER)
           ---------------------------------------

Coming events
-------------
1994

May           14th-15th      Volta RTTY WW Contest

June          11th-12th      ANARTS WW RTTY DX Contest

              ------------------------------------  

Society information

The Society may be contacted at :  PO Box 860, Crows Nest 2065
Australia,   for   such  matters  as  membership  and  general
enquiries.  Enquiries  can  also  be made  by  packet  to  the
President  (Col)  VK2CTD,  or the   Secretary  (Pat)  VK2JPA @
VK2RWI or the current substitute BBS.

News  items  may  be  sent to  Broadcast  Officer  PO  Box  60
Blacktown  2148 Australia,  or by packet to VK2JPA @ VK2RWI or
as mentioned above.
Email address for the Broadcast Officer is : 

patl@pitt.conmusic.su.oz.au 

 The  Society welcomes new items on any digital subjects  from
anywhere in the broadcast footprint.   We know we reach ZL and
many South Pacific islands.  We  are looking forward  to  news
from your areas to let other  amateurs know what you are doing
in the hobby. Hope to hear from you.

73s de Pat VK2JPA Broadcast Officer.
That concludes the ANARTS NEWS809  15/05/94.

Inserted by VK2BQS (Jim) Vice-President ANARTS
