Re: LF: 136 JT9-10

["Graham" <g8fzk@g8fzk.fsnet.co.uk>]

Would be gain 10*log(30/10) = 4.77 dB SNR when going from JT9-10 to JT9-30, assuming there is no negative effect due to QSB and so on? Would someone be interested in tests in JT9-30?

 

S..

 

I think that's  a very difficult  question  to  answer ... this time , last  year  in the  Op development  phase (not phase cont) such  calculations  did  predict  expected  performance's  but  in real  circuits   the  results  varied greatly

 

One  major  factor  is the  modes  ability  to  withstand  data (BIT)  loss  during  qsb  , this  is  a  function  of the   time  hopping  signal shuffling  aspect  , FEC  and  the  demodulators   ability  to  capitalise  on short  burst's  in  propagation ,  from the  various  qrsss   plots  the  signal  on 136  over  range  is  never constant , so fec  would  need  to  cover the  expected  outage  times and the ability to  recover  data  randomly   along the  time  line

 

Thinking  at  90 deg  , this  could  be the  downfall  of  'small'  packet data  modes  , where  a  compressed data  block  'has to be'  transmitted  in a  given  time  window  .where  as  a  conventional   free  running  data  system may  employ  many  layers of   fec and numeric  signal  shuffling  to  ensure , qsb/muti path/  doppler   affects  are  combated  .. the  play off  being  data  rate / speed /s/n  ..  and time  / frequency stability ..  which  in turn  limits user access .. no point  in having  a  mode  that  only  a few  stations  can  use  ?   

 

G..

From: Stefan Schäfer

Sent: Friday, November 30, 2012 1:42 PM

To: rsgb_lf_group@blacksheep.org

Cc: Vasily Savchenko ; Joe Taylor

Subject: Re: LF: 136 JT9-10

Hello LF,

Thanks to DF6NM, RN3AGC, F5WK, DF2JP, UA0SNV, SV8CS, W1VD, LA5VNA (and those which i forgot to mention) for the JT9-10 reports on 137.42 kHz!!

I guess that was a first TA crossing in JT9 on LF. Jay, did you have local QRN or was it a quiet night? Did you try to watch the signal in a spectrogram? How many decodes did you get in the night? Or was it the only one? 23:30 is normally the time where the band opens between us these days, so i guess there have been a number of further decodes. Looking forward to that :-)

Would be gain 10*log(30/10) = 4.77 dB SNR when going from JT9-10 to JT9-30, assuming there is no negative effect due to QSB and so on? Would someone be interested in tests in JT9-30?

I guess this evening is reserved to MF CW here but late in the night i could run some JT9-30 sequences. MF alternatively.


There have been further decodes at UA0SNV (5760 km over land):

All that I received today.

1949   0  -38   2.2 1419.65  -1   DK7FC JN49IK
2009   3  -35   1.3 1419.62   0   DK7FC JN49IK
2019   2  -36   1.7 1419.56   0   DK7FC JN49IK
2149   5  -32   2.6 1419.65   1   DK7FC JN49IK
2159   3  -34   2.6 1419.65   1   DK7FC JN49IK
73 !! Vasily.

Best 73, Stefan/DK7FC




Am 30.11.2012 00:32, schrieb jrusgrove@comcast.net:

Bingo

2329   3  -34   0.0 1419.83   0   DK7FC JN49IK

http://www.w1vd.com/grabber.html

Jay W1VD  WD2XNS  WE2XGR/2