[HCRA] FW: [VWS] International Space Station in Cross-Band repeater mode!

[Daniel Sullivan]

----Original Message Follows----
From: Iain McFadyen <mcfadyenusa at yahoo.com>
Reply-To: VWS at mail.viennawireless.org
To: vws at mail.viennawireless.org
Subject: [VWS] International Space Station in Cross-Band repeater mode!
Date: Fri, 22 Jul 2005 06:26:51 -0700 (PDT)

Good day!

I want to report to the list that the cross-band repeater on board the 
International Space Station has been re-activated, as of Wednesday 
afternoon. It has been a long time since this mode was active. For the 
majority of the last year, the equipment has been in a 'packet' mode.

The cross-band repeater uplink (from ground to ISS) is 437.800 MHz, FM.
The downlink is on 145.800 MHz.  FM

No PL tones required. Instead, the one critical issue which has to be 
addressed is doppler.

For a typical pass, you will have to adjust your transmit frequency on the 
uplink, to take care of the +/- 9kHz doppler effect. Initially, as the ISS 
comes over the horizon into view, you must transmit around 9kHz below the 
nominal frequency: i.e. 437.791 MHz

As the ISS flies overhead, or as it reaches its closest point to you, your 
uplink frequency must be adjusted back to nominal (437.800). And as the ISS 
disappears over the horizon, moving away from you, you must adjust your 
uplink to around 437.809 MHz.

On the downlink, the doppler is less noticeable, and generally, your FM 
receiver will successfully receive the downlink signal for the whole pass, 
even if you leave your receiver tuned to 145.800 for the whole pass. But 
tuning up to 145.803 at "acquisition of satellite" , and slowly tuning down 
to 145.797, may give you a slightly better receiver signal.

A typical pass lasts around 8-9 minutes. The ISS is 250 miles above earth.

To track the ISS, you can use any of the available satellite tracking 
programs. I use Satscape (free, available from http://www.satscape.co.uk) , 
but there are plenty of others to choose from. If you do not want to 
download such a program, there are other sites which will give you 
information: www.issfanclub.com has a tracking page, (but it is offline at 
the moment for some reason. Go to the issfanclub.com homepage, click 
'tracking', then enter your city name. I use "USA" and "McLean" (Don't put 
the state in the search window)).

Another site which gives good orbital pass predictions is 
www.heavens-above.com . You either register, or use the anonymous mode. If 
you drill down through the ISS pages, it will give you the NEXT pass of the 
ISS, or the next 'visible-to-the-naked eye' pass. Not quite so helpful. It 
is really aimed at visual observations of planets and spacecraft.

Today's passes for this area will commence at 11:15, 12:48, 14:24, 16:01, 
17:37, 19:13, and 20:48 EDT.  So we should hear the ISS whilst driving to 
tonight's meeting!!

Regrettably, the ISS receiver squelch is set rather fierce, so a fair amount 
of power is needed to open the squelch. I have been unsuccessful using 
5watts on UHF. But I can hear the ISS clearly on a HT with a rubber duck on 
every pass. So, blow the cobwebs off those 70cm amplifiers, and give it a 
try!

If anyone needs help setting up Satscape, just contact me and I'll help out. 
It really just needs you to set up your own Lat/Long and accurate time.

NOTE
The rate of change of the observed signals from the initial frequency to the 
final frequency, is highly dependent on the elevation of the pass: If the 
pass goes directly overhead your location, then your uplink frequency should 
remain almost stable at 437.791 till almost half way through the pass, then 
during a period of about 1 minute, you will have to move your transmit 
frequency down up to 437.809, then for the remainder of the pass, your 
transmit frequency will remain at 437.809.  If however the pass is very low 
on the horizon, then the rate of change of doppler remains almost constant 
all the way through the pass.

Good luck!

Iain   KI4HLV


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