[amsat-bb] Re: bird to bird fun

i8cvs domenico.i8cvs at tin.it
Fri Aug 29 06:01:04 PDT 2008

----- Original Message -----
From: "SV1BSX" <sv1bsx at yahoo.gr>
To: "i8cvs" <domenico.i8cvs at tin.it>; <w7lrd at comcast.net>; "AMSAT-BB"
<AMSAT-BB at amsat.org>
Sent: Thursday, August 28, 2008 9:34 PM
Subject: Re: [amsat-bb] Re: bird to bird fun

> Hi Domenico, Bob & all
> it's a nice idea but I am thinking also that, the relay between AO-7 &
> FO-29 needs UHF Uplink and UHF Downlink as well !
> Therefore, we need two UHF systems (TX-RX) working simultaneously
> for Full-Duplex operation.
> And even if the AO-7 Uplink is 3.7 MHZ lower than FO-29 downlink,
> we need two antennas in the same band  and probably
> a repeater-style  *Hi-Q duplexer* in order to avoid the desense.
> Or just a UHF antenna and a circulator dr Domenico ?
> Difficult components for the most of us!

Hi Mak, SV1BSX, Bob W7LRD & All

It's not a problem for me Mak because I currently use a 70 cm TX only
connected to a RHCP 10 turn Helix antenna and another different RHCP
10 turn Helix antenna connected to a 70 cm RX only and both Helices are
separated about 10 meters over the roof.

I tried to transmit to AO-7 uplink at 432.150 MHz center frequency with
about 100 watt without experiencing desensitivity at 435.850 MHz downlink
center frequency of FO-29 even using a low noise and high dinamic range
homebrewed cavity input GaAsFET preamplifier.

> However, it's a great challenge. For example @ 18:30 UTC the overlap took
> place between the 2 footprints  over W.Asia.  From E.Canada, Atlantic
> Ocean, Europe, Asia upto E.Siberia it was  possible a QSO... !

But at 18:30 UTC of day 28 august during the overlap the orbit of AO-7 was
ascending northbound while the orbit of FO-29 was descending soutbound so
that the relative speeds by which each satellite see at the other one add
togheter and this make the doppler shift compensation another challenge to
play with.
> Amazing distance for LEOs !  Can you imagine that ?!?!?
> Yes, I know..  it's difficult, yes.   But a great-great challenge for the
> hibernal months !
> And the AO-7 is working 24/7 for the next months - out of eclipse.
> Great opportunity !
> 73 de Mak, SV1BSX

OK Mak, we will try on CW as soon you are ready to go.

73" de

i8CVS Domenico

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