ISS Packet

Discussion of operations on the VHF/UHF bands - repeaters, terrestrial, satellite, EME.

ISS Packet

Postby Jamie_WB4YDL » Sun May 01, 2011 8:54 am

A recent article in CQ Magazine by Don N2IRZ inspired me to write this article. I could put this in the Field Day area as this is how we make our satellite QSO during Field Day. However, you can do this any day of the year - not just Field Day - so here it is in the VHF/UHF Forum. ;) The International Space Station has for years now maintained a packet station similar to the Kenwood D-700 transceiver. It runs in three modes: Roundtable, Mailbox, and APRS. For this discussion, we'll concentrate on the Roundtable mode, which is more commonly called Unproto Mode. Unproto Mode (UI Mode) makes use of AX.25 packet bursts called Unconnected Information or UI. This is a burst of packet that is sent "in the clear", and unnumbered. This means that no acknowledgement is expected or desired. This is quite similar to how APRS works only that APRS has a bit more formatting to send more information. What we want to do is send and receive these UI frames of information as they are repeated, or digipeated, by the packet station on the ISS.

Before we get to the "brass tacks" of how we're going to do this, let's look at the hardware requirements. Do you have a TNC (terminal node controller) ? If so great, but you don't need one ! :!: Nowadays, you can produce packet bursts by a computer sound device and send these out as audio tones to your radio. This requires a simple sound card interface between your computer and your 2M FM radio. This can be Rigblaster or Signalink-type device, or a homebrew interface. Next you need a 2M FM transceiver capable of producing 25-50 watts. The frequency of operation is 145.825 MHz Simplex. The only other component is an antenna. Most folks believe that you need high gain Yagi beams with alt-azimuth directional control. This is not necessary and, in fact, not desired. :o In fact, you will do better with a simple GP vertical antenna. This is what we use during Field Day. Now if you have a hardware TNC such as a Kantronics KPC-3+ (, just interface it as you normally would terrestrial packet and go for it. ;) It fits in the palm of your hand and can run on an internal 9v. battery. 8-)

So let's go to the computer and download some software that will make it easy to make packet contacts via the ISS. First off, if you have a hardware TNC, you don't need anything more fancy than a simple terminal program such as Hyperterminal. Most host mode programs also allow you to operate the TNC in Unproto (UI) Mode. But let's take a look at a program that's been around for nearly a decade and is very popular for this application. That would be Guy Roels ON6MU's UISS software This is an excellent program that takes a LOT of the work off the table. An excellent YouTube video of the setup is here - There is a lot you can do with this simple program, but concentrate on just the ARISS part. Now, you will notice that UISS requires the AGW Packet Engine. This can be downloaded here - This has to be running in the background before UISS becomes fully functional. Behold the YouTube video that shows you how to do this - :geek:

Once you have it all setup and functioning, it should look something like the following image:


In the upper left of the image, there is a drop-down box for "To:" and this should be changed from APRS to CQ. In the "Via:" field, you can leave it ARISS as this is the alias for the ISS callsign RS0ISS.

OK, so you have the hardware and software set up and ready to go. Excellent !! :D All we need now is the ISS to actually pass over and make itself available to us. How do we know when it will come over our location ? There are numerous ways to track the ISS and a simple Google search will reveal the lot of them. For real-time tracking, I like Heavens Above - You may also want a full-functioned satellite tracking program to track all manner of "birds". A free, well-featured one is Orbitron - When the ISS is ready to break your horizon, you will want to turn your radio squelch down so you hear the white noise background. Soon you will hear the packet bursts, and the screen will fill up with messages. You will use the "Text/data" button to send the message you have typed in that field. You can save many canned messages, but you will want to respond to a particular call sign and type it in as part of a reply. If you get a response back from that ham, you have just made your first ISS packet QSO ! :mrgreen:

It takes a little practice and a few passes to get it all down, but it is a lot of fun. The ISS has quite a footprint, and if you catch it on a low pass your contact may be well over a thousand miles away. :o For more information on this little adventure, check out the AMSAT ARISS page - - and the ISS Fan Club page -

73, Jamie
Posts: 46
Joined: Sun Nov 14, 2010 8:45 am
Location: Union City, TN

Return to VHF / UHF Forum

Who is online

Users browsing this forum: No registered users and 1 guest