I would like to collect on this page all the information about using the repeater on board the ISS (International Space Station) and other operating satellites (PSAT) to transmit APRS packets.

Introduction

On board the international space station there is a radio station Kenwood D710, operating with the call sign RS0ISS.
It operates on board the ISS in automatic APRS digital repeater mode. Modulation - AFSK 1200 bps, frequency 145.825 MHz. If the ISS is in line of sight, a radio amateur can transmit an APRS packet aboard the ISS, which can be responded to by other radio amateurs. The connection is counted if the packet was relayed through the ISS - the symbol * is added to the APRS message - a sign of relay.

ISS orbits

Calculation of the time of future orbits for your locality can be performed in Linux in the program gpredict
or on the website https://www.amsat.org/track/index.php.

For work, I use the Xastir + soundmodem programs, as described in the previous article. Compared to terrestrial APRS 144.800, the changes in settings are as follows.

Configuring Xastir for APRS via ISS

To work through the ISS in Xastir, you need to add a second interface to the Interfaces menu - a copy of the one previously configured for 144.8.

)

In the second interface (which is turned on during the ISS flyby), you need to edit the fields:

• first field "path" replace the usual value WIDE 2-2 with ARISS.
• indicate ARISS in the comments (note to yourself that the interface is for the ISS).
  )
  Notes:
  1. path can contain two values, for example,ARISS,PSSAT, but the packet relay on the ISS uses only the first value - i.e. ARISS. The longer the path, the longer the transfer, so it is better to shorten the path as short as possible.
  2. in my opinion, and data from the qrz.com forums, ISS won't answer, if "RS0ISS" or is specified - this erroneous value does not work. It also makes no sense to add the word APRS in front, for example APRS,ARISS - extra characters clutter the path line and do not improve performance.

The ISS repeater will itself insert its call sign RS0ISS and an asterisk (*) into the relayed Space-to-Earth message. The asterisk symbol means that the packet was received and relayed from the ISS.

Procedure for packet radio communication through the ISS

Messages for the ISS are divided into groups:

1. GPS coordinates via APRS. (“GPS beacons”) without specifying the addressee. Optional.
2. text APRS messages for QSO. Such as directed calls To: CALL. -Recommended.
3. non-APRS messages - for example, a regular PACKET sent from a terminal, for example, a BBS (not recommended)
4. service APRS messages (direct station request) - not recommended. Examples of such messages: ?APRST ?IGATE

The simplest thing is to transmit your coordinates at the moment of passage of the ISS (command Interfaces - Transmit Now!) GPS coordinate positions - they will be relayed through the ISS and displayed on the map for other radio amateurs.

It is more correct to call using message passing as written below:

Rules for conducting QSOs using APRS messages

General call

Messages to everyone: in the field CALL specify message text C.Q..

Or indicate a specific call sign (directed call) in the CALL field, for example, RZ1PVT.

The message text is arbitrary. You can specify a square or QTH and a name,KO59, op. Vladimir..

Answer a call

In the field CALL indicate the call sign of the correspondent, in the message field (text) - any response message up to 40 characters long in English. It should be noted that the longer the message, the higher the likelihood of errors occurring when decoding it due to weak level or QSB (signal fading).

Examples of short response messages:
*Hello from SPb

• *TNX 59 73 GL*
  73 de call, CU**

Call signs in the service fields FROM and TO, as well as station coordinates are entered into the APRS package automatically by the Xastir and soundmodem programs.

Packet relay check

The packets relayed back must be received by the receiver and decoded by the program. As with a conventional digital repeater, your packet should be followed by noise - the response from the space station. Then your packet will appear with an asterisk *, which means that it was relayed by the station to Earth.

Packets captured by the ISS (ISS) can be checked on the following websites:
http://www.ariss.net/
http://www.findu.com/cgi-bin/ariss/index.cgi

ISS tracking

The trajectory of the ISS across the sky depends mainly on geographic latitude

LO53ac	KO59ct

Since the city of St. Petersburg is located at 60 degrees north latitude, the height of the ISS above the horizon does not exceed 23 degrees, then working with the ISS at a distance 1100...2200 km, while in the south the ISS at the time of passage is at a distance 435...2200 km.

The moments of station passage (UTC time) can be determined using the QTH locator
*https://www.amsat.org/track/index.php

Calculation of the energy budget of the route

This calculation is not needed if you can work with simple antennas and packets travel on both sides.
In my case, unexpected difficulties arose - the ISS cannot hear and is hard to hear, despite the fact that SWR = 1.1.

(Calculation with gain on the transmitter side (yagi antenna of 3 elements) G=7 dBi, on the receiver side G=0 dBi):

The average signal power on the receiving side is -90 dbm.

The path loss calculated by gpredict - from 139 to 132 dB is included in the same range (134...136db average value).

Conclusion: 3 elements of uda-yaga should be enough to communicate with the ISS (ARISS, RS0ISS) “from horizon to horizon.”

Same calculation for the pin Ground Plane 145.82 MHz(gain is worse than yagi by 5 dB. cable losses are another 2 dB)
It is enough to subtract 7 dB from the previously obtained results. It turns out

Practical measurements of the ISS packet communication level for 2 and 5 uda-yagi elements.

• Vertical polarization - S4...S6.
• Horizontal polarization - S4...S6.
  In vertical polarization I heard it a little louder, by half a point.
  There is no talk of any S9 levels from the ISS in 2020!

• The most powerful signal from the ISS (ISS) is when passing through the zenith. You can use an upward-facing antenna - for example, a horizontal dipole, uda-yagi 2 elements or a turnstile antenna.
• At a space station altitude of 90 to 60 degrees above the horizon, according to messages from the Internet, it is possible to transmit GPS coordinates from portable radio stations to standard “rubber” antennas with low power of 5 W. For example, on Yaesu FT-2DR/DE, Kenwood TH-D74 with built-in APRS GPS tracker.
• At an altitude above the horizon of 60 to 30 degrees, at medium distances, you need to add 10 dB to the pin gain - 3-5 element antennas (G=8-12 dbi) of fixed (45°) or variable elevation are suitable. The required power is the same 10 W.
• At an altitude of 30 to 10 degrees, the ISS begins to hear your signal worse due to the distance; you need to add another 2 dB to the transmission. For example, increase the power 2-3 times to 20...30 W. For reception, a low noise amplifier (LNA) with a noise figure of NF=0.5 db is highly desirable. Antenna - 6-8 elements.

• When the ISS height is from 10 to 0 degrees, local obstacles (multi-story buildings) may interfere. We need a suburban position with horizon visibility from west to east.
  !!!2. incorrect setting of the PATH field (forms the UNPROTO path) - only ARISS or RS0ISS must be specified. All kinds of WIDE2-2, RELAY, ~~SGATE are erroneous values.
  !!!3. wide modulation instead of narrow. Frequency deviation not set. It is important to carefully select the AFSK modulation width by gradually reducing the volume on the computer until the signal becomes high-frequency and ringing to the ear. On WebSDR you can see that the signal consists of many thin lines, that is, it is clear and not blurry. The local repeater must respond to messages the first time.
  !!!3. The message was too long and was decoded with errors.
  !!!4. correction of the Doppler frequency shift on the transmission has not been performed (although the frequency deviation from 145.825 is small +2 kHz at the beginning and -2 kHz at the end, communication may deteriorate at the beginning and end of the turn due to the Doppler effect).
  !!!5. Losses in cables on the transmitting and receiving sides without the use of LNA lead to poor reception.
  !!!6. A difficult situation with interference on the south side of the house, at the site where the ground station for receiving the ISS is installed (receiver overload from out-of-band emissions, lack of dynamic range, effect of reducing receiver sensitivity).
  !!!7. Unbalanced APRS signal with a lower tone of 1200 Hz and an upper tone of 2200 Hz - uneven frequency response. For example, a lack or excess of high frequencies.

  Links:

• Link modeling, radio budget planning:
• Calculation of loss (db) during propagation in outer space -https://www.pasternack.com/t-calculator-fspl.aspx
• Link budget calculation - see.https://www.pasternack.com/t-calculator-link-budget.aspx
• Converting reception power dbm to divisions of the S-unit reception scale -https://www.giangrandi.org/electronics/radio/smeter.shtml

Practice

For a directional antenna with 3 uda-yaga elements, the signal with a satellite above the horizon of 5-10 degrees is S4 (vertical or horizontal polarization does not matter), for 5 elements it is no higher than S6.
An S-meter level of 4 points corresponds to a power of –123 dBm, although in theory the ISS should be audible in such conditions at -108 dBm even on the GP “pin”. On the same antenna, a short yagi 144/433 MHz, I hear satellites XW-2B and XW-2C up to 5 points on the S-meter. The power of the XW-2B is 20dbm (decibel milliwatt - dBm) or 100 mW into the Ground Plane antenna. The power of the APRS radio station on the ISS at 145.825 turned out, judging by the audibility, even less than that of the XW-2B. Less than 0.1 W. The reception is similar - perhaps they use a 15-20 dB attenuator on board the ISS? This is also confirmed by a photo from the ISS telegram channel, with a photo “on the table before being sent into space” of the Kenwood APRS station. But these are just my guesses; no one has announced the current power of 145.825 MHz in 2020.

Other APRS satellites

Satellite NO-44 - does not work.

Satellite PSAT- Map and APRS packets of the satellite PSAT (NO-84) at a frequency of 145.825 MHz,
height above the horizon in St. Petersburg is up to 10 degrees (flies in southern latitudes and above the equator).

APRS settings: use PCSAT text in UNPROTO path. You can try the text ARISS,PCSAT.
The PSAT transmitter power is only 300 mW.
With a free space loss of 130...140 dB and the specified power, the field strength at the receiving location is -100...-110 dBm or about S7 points.

Sources:

• https://www.amsat.org/two-way-satellites/psat-no-84/ - about NO84
• http://www1.findu.com/cgi-bin/pcsat.cgi - ISS communications map
• http://www.cqham.ru/forum/showthread.php?31478-PSAT-PSAT2&p=1165527&viewfull=1#post1165527 - topic about satellites.

Links to APRS articles and forums via ISS:

• http://www.aprs.org/ariss.html - introductory.
• https://amsat-uk.org/beginners/how-to-work-the-iss-on-aprs-packet-radio/ - a guide for beginners.
• https://www.amsat.org/wordpress/wp-content/uploads/2014/01/AMSAT_Journal_ISS_Packet.pdf - article from AMSAT magazine.
• https://www.fars.k6ya.org/docs/aprs_via_iss.pdf - APRS via ISS
• http://forum.vhfdx.ru/sputniki/aprs-cherez-mks-i-sputniki/ - APRS via satellites.
• http://www.cqham.ru/forum/showthread.php?11624-MKS-via-APRS - main topic about APRS via ISS
• http://forum.vhfdx.ru/sputniki/no-84-(psat)/15/ - topic about NO-84
• https://stationproject.blog/2019/04/20/sat40-part5-new-ic-9700/ - an example of an advanced satellite station.
• http://www.aprs.org/doc/APRS101.PDF - description of the APRS protocol.

About working in the HF bands of 20 and 30 meters

On shortwave APRS uses the same AFSK modulation, but the speed 300 baud and distance between carriers 200 Hz. You can use any tones spaced at 200 Hz, for example, 1600 and 1800 Hz; more precise adjustments are made on the transceiver using the tuning knob.

Due to low solar activity, poor transmission does not make it possible to transmit your coordinates or conduct radio communications using a repeater on simple antennas.

APRS frequencies on shortwave 10147.6,10.149.2,14.098.3 kHz. You can more accurately adjust the transmission frequency using a WebSDR receiver, adjusting your signal to the signals of other radio amateurs on the air.

A good guide about APRS on shortwave:

• https://www.qsl.net/g6gvi/digimodes/hfaprs.html

P.S. After publishing this article, I found on AMSAT that “I’m not the only one with problems” with APRS via ISS:
*https://www.amsat.org/pipermail/amsat-bb/2020-May/077599.html

The answers recommend checking the quality of AFSK formation - supposedly the discriminator of the Kenwood TH-D710 device on board the ISS does not perceive AFSK 1200 signals with emphasized high frequencies (prefers “flat” signals). In my case, the sound in the CAT interface passes through a capacitor, which can result in higher frequencies, the so-called pre-emphasis.
In the case of the 144.800 ground repeater, this does not matter, but the aprs digi ISS turned out to be more picky.

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