A Model for DIGITAL TRANSMISSION and WEAK SIGNAL -
CW SSB TROPO EME RECEPTION as a SYSTEM
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We are pretty sure , that thousands of Radio Link Design Engineers have done
Pathloss Calculations and Co- Channel Interference
Calculations  for avoiding System Disturbances , in times before .

Since we HAVE BEEN / ARE AFFECTED by Amateur ATV REPEATER INTERFERENCES  seen
>>from the Weak Signal Receive Point of View , MORE and MORE Amateur Digital
Transmissions / ATV Repeaters are planned nearby the Weak Signal Bands , and
have also been put in operation , we have done such PATHLOSS CALCULATIONS mainly
FOR THE REPEATER OPERATORS , to show how big , and how far away ,  the
transmitted PA IMD3 IMD5 and Noise Sidebands , disturbing a nearby WEAK SIGNAL
CO-CHANNEL BANDSEGMENT  could be . WE FOUND out , that  thoughts and more
STRINGEND RECOMMENDATIONS and SPECIFICATIONS are needed , for protecting the
weak Signal Modes . - Also A FAIR USE of FM-ATV  D-ATV  DVB-S  QPSK  QAM and
other Broadband Modes should be considered by the Operators starting now
 - even without Recommendations and Specifications .
Linking Repeaters together will increase the Traffic and the disturbances .

JUST HAVE A LOOK TO THE SLIDES . The 23cm  Model is convertable to any other
Band , Frequency  Bandwidth , ERP and Distance .

 See also HOW  EASY the cure will be - for just 1.2 db Insertion Loss of an
 Output Filter ( 15% less Reach Distance )  50db  ADDITIONAL unwanted Sideband
 Suppression will be achieved - this is very effective.....Amateur ATV Repeater
 Operators should be encouraged to implement an Output Filter into NEWLY BUILT
 REPEATERS and RETROFIT INSTALLED REPEATERS....Carefully designed PA's or even
 A-Class Amps will Reach just around 40dbc . PA Linearizing Methodes seems to be
 only available for Professional PA's - and 10 to 20db more Sideband Suppression
 will not cure the Problem completely.

Slide 1.......9  are showing the Model , and the Solution needed
( Output Filter and Specifications )  it's really HUGE IMD3 or ACPR
( Adjacent Channel Power Ratio ) LEVELS at the RCV  . The IMD3  etc  dbc Levels
have been taken from Slide PA 1  and Slide REP 1 as a worst case.
...but eg. 10db better dbc IMD levels is not the cure - around 80db are needed

Slide 1     gives a Rule of Thumb Figure , developed from the 23cm System Values
            Input .
Slide 2     is a Fast Path through Digital Modulations , mainly  QPSK ( DVB-S )
            showing, that QPSK is a special kind of AM Modulation (4-QAM)
          - see the Peak Power , with more stringend linearity needs to the PA
            than a SSB PA would provide .
Slide REP 1    is showing the Emission of an OLD DAYS Real World Repeater
               operating 2004 .
Slide REP 2    would have been the cure  ( Output Filter ) .
Slide PA 1     by allowance from Hank PE1JOK  (D-ATV.com)
               showes the AM (Trajectory Oversoots) and PA Back Off need
               also named Output Back Off  ( OBO ) - OBO is needed because of
               Baseband RRC Filter Overshoots and PA non-linearities .
Slide FILT 1   showes the Temperature Behaviour of an ID-Elektronik Filter
               for us it's great !!

THERE IS AN ERROR ON SLIDE 9  The Recommendation (Specification Slide).
  The right Definition for the Recommendation is
 -34 dbm ERP in 10 Mhz ( since the Xmitter Bandwidth / Sidebands have been
  defined with 10 Mhz BW ...also the RCV Bandwidth on this Slide has been
  defined with 2.7 Khz Bandwidth giving the Matchfactor of -36 db )
  The -34 dbm ERP in 10Mhz BW  is equal to an ERP of  -104 dbm/Hz .
......No one is perfect.We would like to apologize in advance for other errors .

For not line of sight or cities other pathloss calculation models apply
...eg. a simple model is to add 12db instead 6db attenuation when doubling
the distance ,  starting at the point , where the first fresnel ellipsoid just
touches the ground .

15-FEB-2007                           Best Regards - Greetings from Vienna

     Walter Worischek ((walter_worischek at gmx.at)) /
     Christoph Libowitzky ((c.libowitzky at kabsi.at))

© 2007 W. Worischek / Ch. Libowitzky - free with reference only for non-professional use.


© 2007 W. Worischek / Ch. Libowitzky - free with reference only for non-professional use.

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