[amsat-bb] Re: requesting help on a RF link solution (imaginary ka-bandlink!)

i8cvs domenico.i8cvs at tin.it
Wed Oct 28 10:13:43 PDT 2009

  Hi Bob, W7LRD

  I need to answere your question as well via AMSAT-BB because my emails sent to w7lrd at comcast.net are alwais rejected to me by your provider. 

  From the point of view of Amateur Radio the best I can suggest to you is the book  " The Satellite Experimenters Handbook " by Martin Davidoff K2UBC 2nd Edition ARRL Order No 3185  ISBN 0-87259-318-5 and also the ARRL " UHF MICROWAVE Experimenters's Manual" ARRL Order No 3126 ISBN 0-87259-312-6 

  Those books  are  full of easy calculations and you can follow it using a small scientific hand held calculator but very important  every chapter of the UHF MICROWAVE Experimenter's Manual is full of "References and Bibliography " that you can find and read/study  to go deeply into details on the above matter covering circuits and antennas which are described here in hardware but also with related easy to follow calculations.

  At the beginning you must go slowly with the above two books but after a few months you will improve and the above matter will come very familiar to you provided that you implement your knoledge following the recommended References and Bibliography.

  In AMSAT-BB I  follow your experimental activity particularly into the S band.............congrats !

  Best 73" de

  i8CVS Domenico 

  ----- Original Message ----- 
  From: Bob- W7LRD 
  To: i8cvs 
  Sent: Wednesday, October 28, 2009 3:23 AM
  Subject: Re: [amsat-bb] Re: requesting help on a RF link solution (imaginary ka-bandlink!)

  Hello Domenico

  I enjoy your posts, even though many are "out of my pay grade".  Would you aim me towards a good tutorial place you may know of where I could learn some of the basics.  I would like to gain a better understanding of this concept.

  Thanks & 73

  Bob W7LRD

  ----- Original Message -----
  From: "i8cvs" <domenico.i8cvs at tin.it>
  To: "Samudra Haque" <samudra.haque at gmail.com>, "Amsat-bb" <amsat-bb at amsat.org>
  Sent: Tuesday, October 27, 2009 5:44:14 PM GMT -08:00 US/Canada Pacific
  Subject: [amsat-bb] Re: requesting help on a RF link solution (imaginary ka-bandlink!)

  ----- Original Message -----
  From: "Samudra Haque" <samudra.haque at gmail.com>
  To: "Amsat-bb" <amsat-bb at amsat.org>
  Sent: Tuesday, October 27, 2009 11:03 AM
  Subject: [amsat-bb] requesting help on a RF link solution (imaginary

  > Hi, amsat-bb
  > CQ any satellite link budget expert !
  > I'm trying to do a calculation on my own based upon published specs
  > for the NASA MRO Ka-band experiment, but am getting some unexpected
  > results for a Ka-band simplex link with Temp=3000K (hypothetical),
  > operating with a Signal to Noise ratio (unitless) figure of 1.171
  > (representing 4.5 dB eb/no with a data rate of 1 Gbps and a bandwidth
  > of 2.4x10^9 Hz)
  > Question : is 1 gbps not 1x10^9 bps ?
  > Question : if both antennas are 3m parabolic (both are the same type)
  > with 56.4 dBi boresight gain, what would you think the furthest
  > distance the link can perform with SNR of 1.171. I have actually used
  > a padding of 3 dB Eb/No in my link budget, so am not worried about any
  > further signal loss at first (ok, I should be ..) For the exercise, I
  > am choosing a 10 Watt estimated output on an arbitrary basis.
  > So:
  > P_t = 10W
  > G_t = 56.4 dBi = G_r , can we assume the same gain for TX and RX on a
  > parabolic dish ?
  > T = 3000K at receiver
  > SNR = 1.171 required
  > f=32.2 GHz
  > B = 2.4E9 Hz, (bpsk, ldpc code 0.5)
  > DR = 1E9 bps
  > So, I am puzzled why this link budget says the range with these
  > parameters is equal to 4.644 x 10^9 Km -- that seems to be a long
  > distance ! What am I not able to conceptualize.
   > BTW, I know if I send this out, the answer will come to me soon
  > thereafter, but for education, I would like to know where the problem
  > in my understanding lies !
  > Samudra N3RDX

  Hi Samudra, N3RDX

  If I well understand your question is to know what is the maximum
  free space distance at which you can get a S/N ratio of 4.5 dB using
  two identical  transmitting and receiving systems having the following

  1) Antenna gain for TX and RX = 56.4 dBi at 32.2 GHz

  2) Frequency = 32.2 GHz

  3) Overall receiving system noise temperature: T = 3000 kelvin

  4) Bandwidth of receiving system = 2.4 x 10^9 Hz

  5) TX power 10 W

  6) Required Signal to Noise ratio S/N at the unknown distance = 4.5 dB

  With the above data we first calculate the receiver noise floor Pn = KTB

  K = Boltzmann constant = 1.38 x 10^ -23 (Joule/kelvin)
  T = Overall System Noise Temperature = 3000 kelvin
  B = Bandwidth of receiving system = 2.4 x 10^9 Hz 

  Working out the numbers we get the following RX noise floor 

  Pn = (1.38 x 10^ -23) x (3000) x (2.4 x 10^9) = 1 x 10^-10 watt

  and 10 x  [ log   (1 x 10^-10)] = - 100 dBW or  - 70 dBm

                                         Link budged calculation

  TX power = 10 W =..................+ 40 dBm
  TX antenna gain ........................+ 56.4 dBi
  Transmitted EIRP......................+ 96.4 dBm

  Free space attenuation for
  61.000 km at 32.2 GHz............- 218.3 dB
  Received power over isotropic
  ant. at 61.000 km distance........- 121.9 dBm

  RX  antenna gain.......................+56.4 dB
  Received power at RX input... - 65.5  dBm
  Receiver noise floor.................- 70.0  dBm
  Received S/N Ratio................. + 4.5 dB


  Using two boresight identical parabolic dishes having each a gain of
  56.4 dBi at 32.2 GHz one transmitting with 10 watt and the other one
  receiving with a receiving system having a noise temperature of 3000 kelvin
  into a bandwidth = 2.4 x 10^9 Hz the free space distance  at which the
  signal is received with a  S/N ratio  = + 4.5 dB  is only 61.000 km so that
  your hypothetical system is not suitable for the NASA MRO Ka-band
  experiment because the distance Earth to Mars is about 1 AU i.e.
  1 Astronomical Unit  corresponding to 149 Million/ km 

  73" de

  i8CVS Domenico

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