Miles Mann, WF1F
April 12, 2001

The Minimum ERP needed to acces ISS packet
will vary between 0.1 watt ERP to 1,000,000 ERP
depending on how many stations are transmitting at that time.

You signal needs to be (all values are approximate) 3-6 db greater
than the noise level at the receiver.  The receiver on ISS
has a hearing range of 1500 miles, in ALL directions.  If there are NO
active
stations on the air at all, then your 0.1 ERP signal will
work for a 300 - 1000 mile distance to ISS.
The best times for QRP ISS links is when the band is not active,
such as when everyone is in bed sleeping or when everyone is at work.
Evenings 00:00 - 05:00 local time
Week days 10:00 - 15:00 local time

Peak Hours:
Peak hours are all weekend and weekday evenings.
During peak hours, there will be many (50- 100) stations calling
at the same time.  
example: 
lets assume there are 100 stations all running 50 erp.
At any given moment we will assume ten are pinging iss at the same time.
That's a total power of 500 ERP  hitting iss.
Your station will either need to get lucky and ping when no one else
is transmitting or you will need 6db more than the total hitting ISS
or 2000 watts ERP.

QRP is not impossible, its just more challenging.
And always use minimal power

wf1f marex