[amsat-bb] Re: Two satellites passing in the night.... or day.

Tom Schuessler tjschuessler at verizon.net
Wed Jan 25 19:24:28 PST 2012

Thanks Patrick, You and Joe Lowenthal had the same idea and it works for me.
I will make sure that the PL is off and work AO27 only and see how it all
flies.  Pass time is for me AOS about 2000Z on the 11th of Feb.  AO-27 turn
on will be about 5 minutes later.  It will be a somewhat west pass so hope
to be able to work you as K2BSA/5.  There is a point mid pass where the two
birds will be pretty close together.  One benefit is that SO-50 runs 5-10KC
lower than published so that also might help depending on where the dopler
shift is at the time.

Thanks, 73
Tom, N5HYP

-----Original Message-----
From: va7ewk at gmail.com [mailto:va7ewk at gmail.com] On Behalf Of Patrick
Sent: Wednesday, January 25, 2012 9:09 AM
To: Tom Schuessler
Subject: Re: [amsat-bb] Two satellites passing in the night.... or day.

Hi Tom!

> I was doing some prep work for the next Boy Scout Radio Merit badge 
> class we will hold at the National Scouting Museum in Irving, TX on 
> Feb. 11 and was mapping out the AO-27 and SO-50 passes for that day.  
> I was surprised to note that they are almost on top of each other or 
> at least down here not too many degrees apart.  I know this has 
> happened before but since the uplink and downlink frequencies for 
> these two satellites are quite close, I would expect quite a bit of
interference at times to each of them during my pass.
> SO-50 has a weaker downlink power so most likely I suspect capture 
> effect would for the most part wipe it out or at least make the signal
quite noisy.
> Also the issue of antennas like the Arrow that have a decently wide 
> beamwidth on the two meter uplink side will cause issues with the same 
> uplink possibly hitting both satellites at the same time.  Folks with 
> higher gain fixed stations may be able to differentiate each satellite 
> for uplink and downlink but us little portable guys may not.

This happens periodically, and there's not much you can do about the
downlink.  You hope for the two satellites to be in different parts of the
sky, so you can point away from one satellite enough to clearly hear the
other.  The uplink is usually a bigger issue, but you can at least know one
thing - if you transmit without a PL, only AO-27 will hear you.
If you transmit with the 67.0 Hz PL tone, you could potentially be heard by
both satellites.

Depending on how the two satellites are passing by, I usually try to work
AO-27 in this situation.  It's only on for 7 minutes, generally hears
stations better than SO-50, and its downlink has twice the power (500mW) of
SO-50 (250mW).  Transmitting without a PL ensures you are only going to be
heard by AO-27.  Once AO-27 shuts off, then I can turn on the
67.0 Hz PL tone and go for SO-50.

Good luck, and 73!


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