[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Mir, SO-35, RS-18 stuff.]



Roger,

Thanks for the message.

RogerKola@aol.com wrote:
> Mike...that's a great help in figuring out how much power we need to work
> this bird...
> 
> Now if some of the other people who made contacts could tell us their power
> out and antenna situation....it would help equalize access...track it with
> the Real Audio file and everyone could judge for themselves how much ERP to
> run...

My situation the day of the Sunsat pass:
        1 watt pep
        1.75 db line and insertion loss
        15 dbic antenna gain
        13.25 dbW EIRP
        for an approximate ERP of 21 watts

Several factors will affect an actual uplink.  Beams are easy to point,
if the operator knows where the bird is at any point in time during the
pass.  It's kind of like pointing the beam of a flashlight at something
you wish to view.  Any antenna with gain over an isotropic radiator has
gain because it focuses energy in a favored direction.  The higher the
gain, the tighter the focus.

A fellow reported using a JPole with 50 watt, and failing.  Using the 
same calculations, here is his situation:
        50 watts pep
        1.75 db line and insertion loss (assumed)
        5.5 dbi antenna gain (again assumed)
        20.7 dbW EIRP
        for an approximate ERP of 118 watts

The JPole exhibits gain by focusing radiation at the horizon (at the
expense of overhead).  So, this antenna will only deliver the calculated
ERP at low elevation passes.  Also, since it is linearly polarized, it
will be subject to an approximate 3 db (half power) fade as the
satellite rotates.  During overhead passes the signal will pass in and
out of various lobes and nulls, further contributing to signal fading. 
If I required a fixed antenna for LEO use, I'd build (or buy) a QHA,
turnstile, eggbeater or Lindenblad antenna.

Commonly, portable users will use an ARROW (or similar) antenna and a 5
watt HT:
        5 watt pep
        1.75 db line and insertion loss (assumed)
        8 dbi antenna gain (assumed)
        13.2 dbW EIRP
        for an approximate ERP of 21 watts

Again, since the ARROW (and similar) antennas are linearly polarized, a
3 db (half power) fade can be expected as the satellite rotates.  Being
a handheld device, it is easy to point and rotate the antenna for best
signal, although on the uplink, this would only apply to operators
employing a full duplex HT, where they can listen to the downlink and
rotate for best combination of downlink/uplink polarity sense.  Half
duplex users can only hear the difference in the downlink as they
reorient the antenna.

I did not know the actual gain figures for the JPole or the ARROW. 
Please correct my numbers if you know better.

If it would be helpful/educational, I will calculate ERP for any
operating situation, if you send me the power, loss and gain figures.

73, Mike in Fort Myers, FL
 
                                       __\/__ 
    |                              .  / ^  _ \  . 
    |                              |\| (o)(o) |/|
    ^    ---   * -----------------.OOOo--oo--oOOO.------------------- *
   |||   | |   * Mike Gilchrist - KF4FDJ ..... AMSAT Area Coordinator *
   |X|   | |   * P.O. Box 763 ................ AMSAT  member   #31884 *
   [X]~~~|k|   * Fort Myers, FL  33902 ....... ARRL  member  #1781549 *
  /   \  |f|   * http://www.gate.net/~seven77  telephone 941.772.7907 *
 |     | |4|   * kf4fdj@amsat.org ............................ EL96ap *
 |  P  | |f|   * I.S. Professional ..... CNA .... Computer Consultant *
 |  3  |=|d|   *   AO10, AO27, FO20, FO29, RS13, RS15, MIR, E Layer   *
 |  D  | |j|   *    Bringing Oscar demos to the Lee County Schools.   *
 |_____|=| |   * * * * * * * * * * * * * *  * * * * * * * * * * * * * *
  /*X*\  | |   *  Black holes were created when God divided by zero.  *
 ________|_|______________________________Oooo.________________________ 
                                  .oooO   (   ) 
                                  (   )    ) / 
                                   \ (    (_/ 
                                    \_)
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home