[amsat-bb] Re: aprs iss freq: is there anyone out there? UHF works!

Andrew Glasbrenner glasbrenner at mindspring.com
Tue Jul 10 13:05:38 PDT 2012


Hi Bob,

I could easily set up an Igate, but every time I've looked into it I've been turned off by the complexity of the software setup. Is there a one program, easy to configure solution? Audio in would be best, but tnc decode is ok as well.

73, Drew KO4MA

Sent from my iPhone

On Jul 10, 2012, at 3:45 PM, "Bob Bruninga" <bruninga at usna.edu> wrote:

>> Unfortunately, 70cm UHF doesn't lend itself to unattended 
>> SatGate operations like 2m VHF does.  I tried catching the 
>> ISS on UHF and only managed to hear, but not decode, one 
>> packet burst.  I can't imagine anything short of a full 
>> satellite station with automatic azimuth/elevation control 
>> would capture many packets right now.
> 
> Actually the problem is not antenna pointing but Doppler.  With the 18 KHz
> of dopper shift, you are only going to capture packets in the center 1/3rd
> of the pass.  But the good news is that the ISS is ten dB closer to you at
> that time.
> 
> Yes, you will not get as many packets, but they can be strong.  The problem
> is that very few people are using the UHF packet digipeater, so if no one is
> transmitting then there is nothing to hear.
> 
> In fact, listening on UHF (for the center of the pass) can be just fine,
> especially on a 19" vertical whip.  Here are the factors:
> 
> 1) due to Doppler, you are only going to decode packets above say about 30
> degrees (without tuning)
> 2) When it is above 30 degrees, the ISS is 10 dB closer than on the horizon
> 3) When it is above 30 degrees the antenna pattern of a 19" whip (normally
> used on 2 meters) acts as a 3/4 wave vertical for UHF and it has almost 7
> dBi gain above 30 degrees 
> 
> So everything is going in your favor and even better link margins on UHF
> above 30 degrees and the packets should be plenty loud (assuming you
> minimize your cable loss).
> 
> The only BAD news is that the ISS spends more than 70% of all inview time
> below 30 degrees.
> 
> But the GOOD news is that such an IGate station can be natennteded, and with
> no moving parts and I t can be replicated by lots more people due to this
> simplicity.  So instead of having only say 6 unattended APRS IGates on the
> 2m downlink to cover the USA, we simply need more stations. Then the APRS-IS
> system will still capture all packets, though any individual station will
> only hear their own smaller "cone of strength"..
> 
> So we simply need to encourage more IGates and lower "individual"
> expectations while the larger quantity of IGates raises the "system
> expectations".
> 
> Something like that.
> 
> Bob, WB4APR
> 
> On 7/10/2012 10:42 AM, Lizeth Norman wrote:
>> Are there any stations in South America to gate aprs packets to the
>> net from the uhf freq? How does one do this? I've got a few Byonics
>> TT4's from a balloon project.
>> The story: I'll be driving the Panamerica Sur from Lima to Nazca Peru
>> and would like to have the ability to be seen via the net.
>> Norm n3ykf
>> 
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
> 
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb



More information about the AMSAT-BB mailing list