[amsat-bb] Re: EggBeater

Mark Spencer mspencer12345 at yahoo.ca
Thu Apr 16 12:19:33 PDT 2009

>Yes, by definition.  An omni cannot hear most of the amateur
>satellites on the horizon, because there just isnt enough signal
>(except for ISS).  You need some gain to hear them on the
>horizon.  BUT when the satellite gets above 20 to 30 degrees, it
>can be TEN times stronger and then ANY omni antenna will work
>quite well (and you don't have to point it).  

>BUT... plot the amount of time a satellite is in view above 25
>degrees and it is less than 1/4th of the time.

Good point.

One approach I have tried with VO52 is to use two receivers with different antennas for the down link.    (ie, one antenna is a ground plane with a modest degree of gain at the horizion, the other is a horizontally polarized (with respect to the ground) dipole.)    The results are signficantly better than a single omni antenna and one of the receivers is usually able to produce an acceptable signal.  During high over head passes the nulls in the pattern of the ground plane are quite apparent, and the dipole works much better on the high passes, on low passes the gain of the ground plane is helpfull but the signals while readable often won't even move the S meter.   A beam that can be pointed directly at the satellite is an even better solution and is likely more cost effective if you are buying all the gear from scratch and listening to signals that often don't move the S meter can be tiring after a while.   

Still in my view if you can't have or don't want a beam and rotor system you can make omni antennas work for the LEO's most of the time but you'll probably be happier with beams and a rotor.


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