[amsat-bb] Re: Dual Hop

[Robert Bruninga]

> I few days ago now, ANDE-1 and RAFT were 
> simultaneously visible from my QTH...
> 
> Since both satellites Tx and Rx on 145.825 MHz, I 
> wondered whether a dual hop is possible. However, 
> it seems that the satellites are configured to 
> prevent this.

Actually, they are intentinoally on the same frequency and they
are intended to be dual or even triple hop possible (when
PCSAT-1 is working)..  Notice that both satelites respond to the
same path VIA ARISS.  SO you could use the path VIA ARISS,ARISS
and get a dual hop.  This ia also why we invite any other
university or amateur satellite builder to add more spacecraft
on this 1200 baud relay channel (with IARU coordination of
course).

In fact, it was the dual hop concept that was so exciting.  And
if  you check the ANDE-RAFT OPS web page you will see several
dual hops noted between PCSAT-1 and PCSAT2.  The problem with
ANDE and RAFT are their slightly worse link budgets.  ANDE has
no external antenna and uses the spacecraft as the antenna.  It
appears to be about 6 dB worse than PCSAT-1.  And RAFT is such a
small 5" cube satellite that the 2 meter antennas are less
efficient (think HT on rubber duck).  SO the chances of dual
hops with these two are less when you realize that one satellite
has to hear the other (and on the same channel as lots of 50W
ground stations)...

HOWEVER, they are in the same orbital plane and every several
weeks, RAFT passes right under ANDE.  I think within only a few
KM.  SO dual hops are DEFINITELY possible but more rare than
with PCSAT-1 and PCSAT2 which were over 2700 miles apart for our
longest dual hop packet to date.

See:
http://www.ew.usna.edu/~bruninga/ande-raft-ops.html

WB4APR, Bob