[amsat-bb] ISS Contacts

AJ9N at aol.com AJ9N at aol.com
Mon Apr 6 23:52:58 UTC 2015

Hi all,

ARISS school contacts are  performed on confidential uplink frequencies and 
all use the public downlink of  145.8 MHz.  We incorporate multiple sets of 
confidential uplink frequencies  just in case the primary is experiencing 
QRM.  For obvious reasons, that is  as much as I am going to tell you about 
the uplinks.  The public uplink  frequencies that are posted are for general 

We have had  interference in the past that was accidental, some flat out 
deliberate, and some  that would be considered deliberate.  In some parts of 
the world, the 2m  band is being illegally used by taxi cabs and who knows 
what else.  Over  the course of the years, we have had to move our uplink 
frequencies around due  to the continued interference.  

Don't forget that the ISS can hear  a lot more than those of us on earth.  
So what you may think is not a  problem locally, could be a big time issue 
for the crew.  Your footprint  radius may be 100 km or so; theirs is about 
2400 km.  They sort of have a  really nice antenna height.

As for possible Field Day operation by the  crew, that is anyone's guess.  
We tell the crew the dates and times and it  is up to them to decide whether 
to participate or not.  We can not make  them participate.  The only thing 
we can suggest is to listen and if you  hear the ISS on during FD, then go 
for it.  The same goes for just general  listening.  If you hear them, then 
go for it.  You do need to be aware  of the FM capture effect and do make use 
of Doppler correction.  For the  ARISS school contacts, we present a 
proposed list of times for the schools to  prioritize so that we can give them to 
the ISS planners and hopefully have one  get scheduled.  Those times are in 
the 08:00 to 19:30 UTC timeframe.   So that will give you an idea of when 
someone could possibly be on.

Hope  this helps a bit.  Just remember that ham radio is only a guest on 
the  ISS.

Charlie AJ9N
One of the ARISS mentors

In a  message dated 4/6/2015 2:00:39 P.M. Pacific Daylight Time, 
dan at post.com  writes:
Info on frequencies  here.


I think they also  have a backup frequency that is not published. They
have had interference on  both uplink and downlink in the past possibly
accidentally. The exact time of  school contacts and normal downlink
frequency is usually very well advertised  in the country where the
contact will take place.

Sometimes, including  one recent contact in Italy they actually
re-attempted the contact at the  next pass 90 minutes later as there
was interference. They try throw lots of  power and gain on the uplink
in an attempt to drown out any accidental or low  power interference.

On 06/04/2015, Daniel Estévez  <daniel at destevez.net> wrote:
> El 06/04/15 a las 17:12, John Brier  escribió:
>> fwiw, I do know not to interrupt during scheduled  ARISS contacts. I
>> was telling someone else who responded to me that  it was a good thing
>> they don't publish the uplink frequencies not  only so people don't
>> intentionally try to take advantage of the  situation, but also so
>> ignorant (and excitedly blind people like me)  don't interfere.
> Sorry if this has been asked before, but are  not the uplink frequencies
> 145.20 for region 1 and 144.49 for regions 2  and 3? Or do they use
> different uplink frequencies for scheduled  contacts?
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