April 5, 2006

How to use the Amateur Radio "Round Table" via the International Space Station Alpha

By G. Miles Mann, WF1F MAREX

With contributions from:
Frank Bauer Chairman ARISS and Bob Bruninga WB4APR

The New Amateur Radio Kenwood D700 Packet/Voice project on the International Space Station was activated in December 2003 and is still in operation.

The name of the International Space Station new Amateur Radio experiment is the "Packet Radio System " or PRS. The ISS PRS experiment is designed to allow beginners, easy access to the International Space Stations educational Amateur Radio experiment. If you have an existing Amateur Radio 2-meter packet station at home now, then you may already have all of the equipment you need to meet new friends around the world or start a friendship with the Cosmonauts and Astronauts on board ISS.

The ISS Packet Radio System supports three different modes, Personal Message System, Round Table and APRS. In this article I will describe the equipment you need to operate the Packet Radio Systemsí "Round Table" mode on ISS. The other supported modes, Personal Message System and APRS will be covered in separate memos and I will provide URL links for additional APRS information.

Round Table (aka Unproto):

The "Round Table" mode is a keyboard to keyboard form of communication. Round Table will allow you to type short messages, which will be relayed (a.k.a. Digitally Repeated or Digi for short) through the PRS and retransmitted over a distance in excess of 1000 miles. Round Table mode allows many people to participate in a Round Table like environment while the ISS is in range. The Amateur Radio call sign for the Round Table mode is ARISS or RS0ISS.

Personal Message System (Packet Mail):

The Personal Message System (a.k.a. PMS or Mailbox) mode allows you to place a short personal message directly into the PRS system on ISS. Once the message is Saved, the ISS crew can read and or reply to the message.  The PRS Amateur Radio call sign for the Personal Message System mode is RS0ISS-1.

At the present time the D700 mail box is operational, however due to packet processing delays being experienced by the D700, it makes the Mail box option very difficult to use. The Round Table / Unproto features are significantly easier for beginners to use and are not impacted as much by the processing delays. 

APRS (Automated Position Reporting System)

The APRS mode is no different from the Round table mode except that APRS software on the ground is used to pre-format the message lines into some special formats for conveying position data, map objects and other short messages between users. For more information on APRS, please refer to the following URL



There are two packet hardware platforms currently on ISS at this time. You will need to check the ARISS/AMSAT/MAREXMG web pages to find out which one is active and on which frequency. The two packet systems are similar, however there are some differences. You should take the time to review the information presented here that will improve your successfulness.

Ericsson PacComm System: (Inactive)

The Ericsson System is single band 2-meter radio transceiver and a PacComm Terminal Node Controller AX.25 1200-baud packet modem (usually just called a TNC or a Modem). The radio is currently connected to an externally mounted mono band antenna (two antennas on opposite sides of the Zarya (FGB), co-phased together and tuned for 147 MHz). The typical power output of this system is 4-5 watts. This system was used extensively by Cosmonaut Valery Korzun in the fall of 2002.

Kenwood D700 System: (ACTIVE)

The Kenwood System uses a newer transceiver that has a built in packet modem. This system is located in the Service Module. The Kenwood model D700 supports two Amateur radio bands: 2-meter FM (144 Ė 146 MHz) and the 70 centimeter FM (434 - 438 MHz). The built-in modem or TNC supports 1200 and 9600 baud data rates. The new system is connected to one of the 4 new Amateur Radio antennas mounted outside of the Service Module (WA1 antenna Module, Earth Facing). The default power output of the Packet system is 10 watts, (other power levels are manually selectable at  5, 10 or 25 watts). The new Kenwood D700 system was activated in December 2003 running 1200 baud mode and voice modes.

To work ISS from your home, you should have at least the following Amateur Radio equipment. A 2-meter radio with an output rating of 25 to 50 watts or more. An omni-directional antenna or small beam. A short run of good quality coax (RG-213, 100 feet or less). And a standard 1200 baud AX.25 Packet modem (TNC). I use an inexpensive KPC-3 modem for all of my ISS packet connections.

The ISS will use different frequencies, depending on the Mode of operation and the general location of the Space Station. When the Packet modes is active on 2-meters the frequency pair will always be 145.800 down and 145.990 mhz up "World Wide".  Please refer to the chart below for mode and frequency selection for your country.

The following frequencies are currently used for ARISS general QSO's

Voice and Packet Downlink: 145.80 (Worldwide)
Voice Uplink: 144.49 for Regions 2 and 3 (The Americas, and the Pacific)
Voice Uplink: 145.20 for Region 1 (Europe, Central Asia and Africa)
Packet Uplink: 145.99 (Worldwide)

Doppler Shift:

The ISS Space Station is traveling around the Earth at over 17,500-mph (28,000 Kph). This great speed will make radio signals appear to shift in frequency. This phenomenon is called Doppler Shift. Many of us have radios that are Channel locked. This means you cannot make any fine tuning adjustments to your receiver or transmitter's frequency. Most Mobile and HT radios cannot make any frequency changes less than 5 kHz channel steps (lets hope that radio manufacturers will add 1 or 2 kHz channels steps in the future). The Doppler shift will cause the ISS transmit frequency (145.800) to look as if it is 3.5 kHz higher in frequency when ISS is approaching your location. If you listen on 145.805 or 145.795, your reception may actually improve a little (for a 5 kHz radio). You will need to review the owner's manual for your radio to learn how to program "Odd-Splits" channel combinations and program the following consecutive frequencies into your radios' memories.

For 5 kHz channel step radios do not try to adjust for Doppler
( Region 2--North & South America, Region 3Asia, Australia)
Channel 1 145.800.0 RX 144.490.0 TX Voice
Channel 2 145.800.0 RX 145.990.0 TX Packet (Worldwide)
Channel 3 145.800.0 RX 145.200.0 TX Voice (Region 1Europe, Africa)

For VOICE (Region 2 North & South America, Region 3Asia, Australia)
2.5 kHz channel step radios
Channel 1 145.802.5 RX 144.487.5 TX
Channel 2 145.800.0 RX 144.490.0 TX
Channel 3 145.797.5 RX 144.492.5 TX

For PACKET 2.5 kHz channel step radios (Worldwide)
Channel 4 145.802.5 RX 145.987.5 TX
Channel 5 145.800.0 RX 145.990.0 TX
Channel 6 145.797.5 RX 145.992.5 TX

For VOICE (Region 1Europe, Africa) 2.5 kHz channel step radios
Channel 7 145.802.5 RX 145.197.5 TX
Channel 8 145.800.0 RX 145.200.0 TX
Channel 9 145.797.5 RX 145.202.5 TX

Let's assume ISS is approaching your location (QTH) and the packet system is active. Use channel #4 at the beginning of the pass, then when ISS is over head, use channel #5 and when ISS passes your QTH use channel #6. For best results, use an updated tracking program, which displays the current Doppler shift. This will assist you in determining when it is best to change channels.

As you may have noticed, it is not recommended for you to adjust your uplink frequency on 5 kHz radios. You will have better results if you leave your receiver on 145.800 and your transmitter on 145.990 (for packet). The Doppler shift is only at the +3.5 kHz setting for a few seconds, then it will slowly begin to approach zero. After 5 minutes or less, the Doppler shift will be 0 for a few seconds, and then it will begin to swing towards -3.5 kHz.

TNC Configuration:

In the Manual for your TNC, the "Round Table" feature is called "Unproto". To operate the ISS PRS, you will need to modify some of the settings on your TNC. The parameter changes needed for "Round Table" and "Personal Message System" are the same. The TNC parameter changes for APRS are a little different and will be covered in a separate memo. Most of the parameter changes required for ISS PRS will be compatible with terrestrial BBS operations. Using these suggested parameters will improve you're success rate and at the same time help reduce interference (QRM). Note, for information specifically about APRS, please see the URL links below. This memo is for Unproto and Personal Message System settings. You do not need APRS to work ISS Personal Message System or Unproto (Round Table)

These are the suggested TNC settings for Round Table/Unproto and Personal Message System modes for ISS PRS. The settings for the APRS mode are a little different and will be noted below.

PACLEN (Round Table and PMS = 72, APRS = 0)
TIME STAMP (Round Table and PMS = ON, APRS = OFF)
Unproto CQ V ARISS

Make sure your beacon is disabled. Unattended beacons on the ISS packet uplink frequency will just cause interference. You should only transmit manually while you are at controls. Please keep beacons turned OFF, while on the ISS uplink channel. Only call ISS Round Table Manually !!!!

This value seems to interfere with normal ISS BBS operations. Make sure LFADD is turned OFF.

This value is normally turned "OFF" for terrestrial BBS connections and "ON" for connections to the ISS PRS. This value will allow you to see packets going to other stations, while you are Connected to Personal Message System or Attempting to Connect to Personal Message System. All courteous operators using ISS will keep this value ON when using the Personal Message System mode.

Set this value on to monitor all data.
Set this value "ON" if you want to see the details of every single packet. This is very useful while monitoring space packets. But be sure to turn it off if you run APRS or other specialized software.

Allows monitoring of packets while not connected.

PACLEN: 72 (Characters per line)
Short data packets are less likely to be clobbered or corrupted. Some APRS software packages may require this value to be set differently, check your specific APRS application for the correct settings.

You do not want to set this value too high because you may cause interference (QRM) during your initial connect. Also, if "RETRY" is too short, you will time-out during the one of the 4 deep RF signal fades. Foot note 2. During a 10-minute pass, there will be 4 RF polarity shifts in the signal coming from ISS. This shift is caused by the apparent position of the antenna on ISS's in relation to your antenna.


With Time Stamp turned on, you will be able to log data to your disk while you are away and track the time and duration's of the passes. Some APRS software packages may require this value to be set differently, check your specific APRS application for the correct settings.

Unproto Command Format:

The UnProto command has two parts. The first part is the TOCALL and can be one of the generic call signs recognized by most other software programs such as CQ, ALL, APRS, QST. The second part is the letter V or VIA and the third part is the PATH. For ISS this should be ARISS, which is the digi-repeating alias for ISS. If your packet is successfully digi-repeated by ISS Packet system, it will substitute "ARISS" path name for RS0ISS-3 call sign in the downlink copy. The PATH field may contain multiple entries, but only the first PATH is used for ISS, you may insert your Grid square or NAME in two additional fields for example:

Below are all valid examples for configuring the UNPROTO command in your TNC:

UNPROTO for the D700 (Active)
CQ VIA ARISS (Preferred format for the D700)
CQ VIA RS0ISS-3 (Kenwood D700)

UNPROTO for the Ericsson / PacCom system (Inactive)
CQ VIA RS0ISS (Ericsson/PacComm)

Space Station Call sign: December 22, 3003

ISS Call sign:

The call sign of the Packet station has changed several times. As of December 22, 2003 the Mailbox address for the Kenwood D700 was "RS0ISS-11" and the Unproto address is "RS0ISS-3" / "ARISS". The address may change from time to time, please check the ARISS web pages or monitor the down link data to verify the address currently in use. Don't confuse a Zero with the letter "OH",  RS0ISS or rs0iss (that is "rs 0 iss" the value in the middle is the integer Zero)

Kenwood D700 Address (Active)
Mail Box RS0ISS-11
Unproto RS0ISS-3 or ARISS

Ericsson PacComm Address (Inactive)
Mail Box RS0ISS-1
Unproto RS0ISS

Make sure that when you enter the call sign into your TNC Unproto command that you enter the correct call sign (Case is not important r = R)

AX-25 packet frame conventions:

You should try to become familiar with a few of the packet frame identifiers, this will help you understand, what you are seeing. Some of this information should be in your TNCís users manual.

C-Connect request
D-Disconnect request
DM-Disconnect mode
UA-Unnumbered Acknowledge
UI-Unconnected Information frame
I(n)-Information frame (n=0-7).

ISS Round Table procedures:

The ISS PRS (Packet Radio System) also supports the Digital repeating mode called UnProto / Round Table. UNPROTO / Round Table mode is a way of sending packet messages without requiring an acknowledgment (ACK PROTOCOL) from the other station (hence UNPROTO for Unacknowledged protocol). This mode is similar to RTTY in that, you can have several stations in one big "Round Table" at the same time. 

Set your UnProto command in your TNC as shown above.  Verify you have entered a valid Unproto command string.  On most TNC's just type the letter "U" at the CMD: prompt and the TNC will echo back you current Unproto command string.

Example 1:
cmd: U

In this example, setup my Unproto command string with the first part TOCALL set to my first name.  This is completely acceptable.  You can set the TOCALL to any set of characters up to 6 long.  Most stations set the TOCALL to CQ, ALL, APRS, QST or a Grid location.  

The last part of my Unproto command is important, the word after VIA must be a valid path name.  In this case the recommended name for the D700 packet system on ISS is the word ARISS.  In this case the word ARISS is an Alias for the call signs RS0ISS-3.  You will see how the D700 process the data in the next section.

Example 2:
cmd: K††† (Here I enter the letter K at the command prompt to start Unproto)

(I entered a short like of text, followed by the "Return" key. The information I typed is now transmitted to D700 on ISS. This is what the out going packet will look like. )
WF1F>MILES,ARISS [03/30/2006 07:40:03]: <UI>: Hi all†

Notice the order of the words:
(This is who is sending the data)
(This is the Unproto command string, the first Part "MILES" is the TOCALL which is ignored by the Unprot software. The Second part "ARISS" is the address of the TNC you want to Repeat your data. If you do not get this name correct the receiving TNC will ignore you packet data)
[03/30/2006 07:40:03]: <UI>: Hi all†
(The date and time are not really being sent, this just a local Tag that my TNC will display on all date. It does help a lot when you want to read you data logs later. The "<UI>" means this in an Un-Numbered data packet. The Text inside this packet is just the two words "Hi all".)

If the D700 on ISS hears your packet, it will repeat the same packet back to Earth.  Your original packet will be modified slightly, can you see the changes below?

WF1F>MILES,ARISS  <UI>:  Hi all  (Original Packet)
WF1F>MILES,RS0ISS-3* : <UI>:  Hi all (Retransmitted Packet from ISS)

When a packet is retransmitted in Unproto mode from the D700 on ISS, it will replace the "ARISS" path name for the actual packet name for the Unproto port, in this example ARISS became RS0ISS-3.  Also Note the "*" Asterisk.  The Asterisk is appended to the path call sign for every packet that is repeated.  If you do not see the Asterisk, then your packet was not Re-repeated by a Digi.

Example 3:

Below is a short UnProto / Round Table between a station in Massachusetts and Pennsylvania, using the ISS Digi Round Table. The stations were arranging to meet on HF when the ISS pass was over.  In this example, I replaced my TOCALL with grid square location marker FN42, while Tom is using the TOCALL of "CQ".

Typical Round Table exchange from via ISS:

N3CXP>CQ,RS0ISS-3*:     Hi all, great sigs here! de Tom in Allentown, PA
WF1F>FN42,RS0ISS-3*:     n3cxp are u on?
N3CXP>CQ,RS0ISS-3*:      Hi Miles
WF1F>FN42,RS0ISS-3*:     I have the amp on hf 7.215
N3CXP>CQ,RS0ISS-3*:     Just copying the mail
N3CXP>CQ,RS0ISS-3*:     Ok cu after the pass
WF1F>FN42,RS0ISS-3*:     Ok Tom
WF1F>FN42,RS0ISS-3*:     Monitoring 7.215 lsb

The UnProto mode does not guarantee that your message will be successful, but if the ISS Digi does retransmit your line of text, then you can be assured that someone saw it. The line of text you send will be repeated with an Asterisk after it, "RS0ISS-3*/". If you do not see the Asterisk, then ISS did not hear your packet. UnProto does have its drawbacks, but it is much more efficient to use on ISS than the Direct two-way connect method. Full two-way packet connects via the ISS PRS are not recommended because they use up too much resources and excessive "Retires". Before you try Unproto on ISS, I recommend that you practice on a Terrestrial Digi first before attempting to use the ISS station for Digi-repeating. If you make a few UnProto calls and do not get any echoes back from ISS, it is probably because the band is too busy. Wait and try later.

For more information on D700 ISS packet operations


Related Web pages for additional Information on Amateur Radio projects on ISS

ARISS web page


Bob Bruninga, WB4APR, US Naval Academy Satellite Lab, ISS APRS web page


Marexmg Home page


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Until we meet again


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