A Model for DIGITAL TRANSMISSION and WEAK SIGNAL - CW SSB TROPO EME RECEPTION as a SYSTEM ================================================================================== 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.Mein Haus im Winter
Conteststandort am Hocheck