HAMTV from the ISS

HAMTV is the name of the Digital Amateur Television (DATV) transmitter on board the Columbus module of the International Space Station (ISS).

It transmits Digital video and audio in MPEG-2 format using the DVB-S protocol in the 13cms band.

The original HamTV unit was installed on the ISS in 2013 and commissioned in April 2014 and was used for a number of ARISS school contacts in 2016 - 2018.

The unit failed in 2019, and was returned to earth for repair. It is expected to be returned to the ISS on the SpaceX SpX-30 flight currently scheduled for March 21st 2024. It is hoped that it will be recommissioned by a visiting astronaut within a few weeks of its arrival.

HAMTV specifications

Ham Video downlink frequencies

• 2395 MHz (main operating frequency)
• 2369 MHz
• 2422 MHz
• 2437 MHz

DVB-S modulation

• Symbol rates: 1.3 Ms/s or 2.0 Ms/s (2.0 Ms/s is normally used)
• FEC : ½

RF output

The HAMTV transmitter produces 10 watts RF, however this is then fed through a series of interconnecting cables and bandpass filter before passing through the ISS Columbus module external wall.

Estimated power at the antenna is ~ 2 watts.

HAMTV antenna

The HamTV transmission runs relatively low power on 2395MHz to a simple patch antenna on the ISS.

This patch antenna is located on the earth facing side of the ISS but there are many other items that project below the antenna and may cause reflections. These include the solar panels, thermal radiator panels, sometimes, two or more visiting vehicles and robotic arms. Depending upon your location in respect to the ISS, these projections may result in strong reflected signals as well as the one from the patch antenna itself. They may cause disturbances to the signal level you receive.

The ISS also “flies” slightly nose down to protect the cupola windows from space debris and so the RF performance, particularly when it is rising from the west, is slightly unpredictable.

The transmissions are right hand circular polarised (RHCP)

Video format

• MPEG-2 Video, approx. 1 Mbits/s
• MP2 Audio, approx 360kb/s
• NTSC
• SIF resolution: 352×240 or D1:720×480, 29.97fps
• Note that non-square pixels are used, the 4:3 picture has to be stretched to 16:9 for correct visual aspect ratio.

What is HAMTV used for?

The primary use is for ARISS schools contacts, when the astronaut will use a camera to show live video of himself and the inside of the ISS to the school during the VHF radio contact.

It is hoped in the future that test patterns, including JPEG images, will be transmitted when the cameras are not in use. Note this will NOT happen when HAMTV is recommissioned in Spring / Summer 2024.

When will HAMTV be "on the air"?

Once re-commissioned, HAMTV will be tested before school contacts are undertaken, however it is unlikely that the transmitter will be left on air 24/7.

During the first flight on the ISS between 2014 and 2018 it was used primarily for ARISS schools contacts but transmitter was left on at other times but no video was transmitted. This did allow ground stations to test their receive equipment and it is hoped a test signal generator will eventually be included, perhaps in 2025.

HamTV will be added to the AMSAT status page https://www.amsat.org/status/ - always check there before doing any receive tests.

How to receive HAMTV?

There are a number of challenges to receive HAMTV from the ISS and a typical ground station is made up of the elements shown in the diagram.

* The LNA / Downconverter should placed as close as possible to the dish feed and high quality microwave cable must be used.
* The upper blue-boxes option is the preferred solution for new builders.
* In the blue-boxes option the line amplifier and filters are at 2.4Ghz and GOOD (not cheap) quality satellite co-ax must be used to avoid the RF level being too low at the receiver.
* The satellite line amplifiers are required to ensure there is enough signal at the receiver input - these may be placed at masthead or in the shack
* The filters are essential, not nice to have!
* The Minitiouner V2 / Pico tuner USB receiver can be connected to EITHER a PC running OpenTuner or Minitiouner software or a Pi4 based Ryde set top box receiver.

See the sections below for a full description of the elements in the diagram.

Ground station antennas

The HamTV transmission runs relatively low power on 2395MHz to a simple patch antenna on the ISS.

This means an antenna with reasonable gain is required to receive the signal and whilst it is possible to receive the signal on a simple antenna when the ISS is overhead, to enable more than 5 minutes of reception, a higher gain antenna such as a dish with an efficient feed system is required.

It will be difficult to receive HamTV DATV picture when ISS is at a low elevation at your ground station location. Generally, a minimum of 20 degrees elevation is required to begin receiving DATV pictures.

A 1 meter or larger dish is optimum. Smaller antennas such as flat plate or patch antennas will work at high elevations when the path length is short and have the advantage of a wider beamwidth making it easier to track the ISS, but they are unlikely to work at low elevations due to the significantly longer path.

Either offset- or prime-focus dishes can be used. Prime focus will be easier to visually align with the rotator axes, but are generally less available and more expensive.

Rotator (mechanical tracking)

Perhaps the most challenging aspect of receiving HamTV is that, unlike the QO-100 satellite available in the Europe and Africa, the ISS is not geo-stationary and orbits the earth every 96 minutes and is visible at any location for a maximum of 11 minutes, often less.

Larger-aperture antennas will result in a stronger signal but require finer steps and more accurate pointing at the ISS as it passes overhead, increasing demands on the mechanical tracking.

The Yaesu G-5500 rotator is commonly used. It can handle up to approx. 1.8m dish, but will require careful azimuth and elevation calibration, and may lose tracking intermittently during the fast (high) parts of the pass. A 1-1.2m dish on a G-5500 is a lot easier to handle and is recommended.

SPID rotators are a lot more capable and can more precisely, however are significantly more expensive.

• 1m dish: 8 degrees beamwidth (+/-4 degrees)
• 1.8m dish: 4.5 degrees beamwidth (+/-2.2 degrees)

Software - Just like for other spacecraft in low earth orbit, there is a choice of software available to control the rotator system. PSTrotator which is a very versatile system with almost unlimited number of interfaces to control rotators is one of them.

Dish feeds

The transmission is RHCP, so the feed on a dish must be LHCP as the polarity is reversed when the signal is bounced off the dish surface into the feed. Any antenna used to receive the signal directly will need to be RHCP.

A suitable helical design for deep dishes was described by G3RUH here https://www.amsat.org/amsat/articles/g3ruh/116.html

There are a number of dish feeds around for QO100 satellite uplink - these are suitable for HamTV reception as they work at the same frequency in the 2.3GHz amateur band.

https://dc8pat.darc.de/rc3/referrers/qrz_dc8pat.html - helical antenna design is at the bottom of the page.

http://f5ad.free.fr/Liens_coupes_ANT/G/PA3FYM%20Helice%202300.htm

It should be possible to use the POTY patch dish feed designed for QO100 uplink. http://www.hybridpretender.nl/poty.html Note - it may be possible to receive HamTV on a dish aligned on QO100 when the ISS passes in front of Eshail-2!

LNA and Pre-amp

A low noise pre-amp (LNA) should be connected directly to the antenna feed point via very high quality feeder to minimise losses. The LNA should have noise figure (NF) less than 1db and a gain of at least 15 dB.

Commercial LNA Options

• Best and most expensive: KU LNA 220240 A - 0.4dB NF, KU LNA 222 AH - 0.5dB NF
• Lower cost (relative), good performance: Minicircuits ZX60-242GLN-S+ - 0.9dB NF

Band pass Filter

Note that 2395MHz is only 5MHz below the 2.4GHz WiFi Channel 1, so good filtering will be needed to prevent strong, local WiFi signals from getting into the wide band satellite tuner and causing interference or de-sense.

It is desirable to put the filter AFTER the LNA so the noise figure of the system is not degraded by filter loss. However, you must ensure the LNA is not driven into compression (overloaded) by the local WiFi signals - if this is happening then the filter should be placed before the LNA at masthead as otherwise the HamTV signal may not decode.

If you are using a downconverter, the filter can be at the IF frequency as long as the downconverter is not overloaded by the WiFi.

Multi-pole interdigital filters work well for this, and should ideally be tuned to provide a low-pass roll-off above 2396MHz.

More information on transmit and receive filters can be found on this wiki page: Filters

Receive co-ax cable

It is recommended to use professional grade satellite co-ax. If you are using a long cable run you must check the received signal level at the receiver - see below.

Receive Line amplifier

Satellite TV receivers need a high level of RF signal - they are designed for use with satellite LNBs which have ~55dB gain. Your masthead pre-amp must be followed by at least one satellite TV line amplifier with greater than 30 dB gain.

Your masthead LNA/LNB MUST have enough gain to overcome your co-ax cable loss.  The satellite line amplifier can be placed at masthead if needed to help overcome the feeder loss or in the shack.  To hear more about the importance of noise figure and gain distribution in a DATV receive system watch https://youtu.be/lfSi7vTQK44?si=wn_wLBjxco3_RnAf

You can check if you have enough gain in your receive system by checking the RF signal level on the Ryde, OpenTuner, MiniTiouner or Portsdown DATV receivers - the noise floor should sit between -30 to -70dBm when not receiving any signals.

If you are powering the LNA at masthead up the co-ax, you will need to place the DC inserter AFTER the filter.

Do I need a downconverter?

The HAMTV frequency on 2395MHz is outside the frequency range of a standard consumer set top box or satellite tuner.

Unless you are using the BATC MiniTiouner Mark 2 or PicoTuner USB receiver equipped with the Serit 4434 NIM, which can tune up to 2450MHz, you will need a frequency down converter to place the HAMTV signal between 950 and 2150MHz which is within the range of a standard satellite receiver.

Note: The MiniTiouner Mk1 PCB with a Sharp or Eardertek tuner does NOT cover 2395MHz and will require a downconverter.  The Seit NIM also has better RF performance than the Sharp or Eardertek units.

The downconverter should be placed between the low noise amplifier and satellite receiver – placing it at the masthead will mean that lower grade feeder can be used to bring the IF signal back to the shack.

Previous suppliers of suitable downconverters, such as Kuhne Electronics, no longer market suitable items and BATC strongly recommends purchasing a new USB tuner hardware kit using the Serit 4334 tuner rather than building or sourcing a down converter - see next section on HamTV receivers.

Digital receivers for HAMTV

The HamTV transmissions can be received using a DVB-S receiver capable of decoding 2 Msymbol / second MPEG2 transmission. This means that a standard consumer Set Top Box (STB) can be used. However, because the signal is only available during the ISS pass it is essential to use a receiver that can be set to both the frequency and symbol rate before the pass.

A receiver, such as a typical consumer STB, that needs to scan the frequency is unlikely to lock to the signal in the time available during the pass. This solution is therefore not recommended.

Receivers designed for DATV

For optimum performance, a receiver designed for receiving narrow band DATV signals should be used. The Amateur TV community has developed a number of receive solutions based around a USB connected tuner hardware.

This USB hardware connects to either a PC or Raspberry Pi 4 via a USB port - software on the PC or Pi4 sets the frequency and symbol rate of the USB receiver hardware and decodes and displays the received signal.

USB Receiver hardware

The BATC Minitiouner and PicoTuner are PCBs which host the Serit 4334 satellite tuner and a USB interface. This unit is designed to be built at home, requiring only intermediate skills and does not use surface mount components.

Mark 2 MiniTiouner PCB

This is the USB hardware which has been available for 7 years and will work well for HAMTV.

For full details of the USB tuner hardware, including parts list and construction details see this wiki page: MiniTiouner hardware Version 2

PicoTuner PCB

The PicoTuner is an enhanced version of the Mk2 MiniTiouner PCB launched in Spring 2024.

It replaces the FTDI USB interface on the original PCB with a Rpi Pico module. The Pico is not only significantly cheaper (£5 vs £32) but enables 2 stations to be received at once when used on the QO100 satellite.

The PicoTuner will be released in April 2024 and it will become the recommended solution for new builders.

For more details see this wiki page PicoTuner

As mentioned above, the original BATC MiniTiouner Mk1 PCB (available from 2015 to 2017) with a Sharp or Eardertek tuner does NOT cover 2395MHz and will require a downconverter. As well as covering the HAMTV frequency without a down converter, the Serit 4334 has much better RF performance than the original Sharp and Eardertek units and has been integrated into the OpenTuner, Ryde and Portsdown DATV receive systems.

Software for use with the USB receiver

The USB hardware described above connects to either a PC or Raspberry Pi 4 via a USB port - software on the PC or Pi4 controls the USB receiver hardware and decodes and displays the received signal.

When the original HamTV was on the air, due to a problem with the DVB tables in the transmission, the MiniTiouner software by F6DZP running on Windows had to be used.

However, during the last few years several developments have taken and so we now have a choice of software to use with the Mk2 Serit 4334 based USB tuner hardware.

Note Open Tuner, Ryde and Portsdown receivers DO NOT support the Mk1 MiniTiouner hardware.

Any desktop PC since approx. 2014, or any mid+ laptop since approx 2017 should be capable of running the required software.

Ryde

Raspberry Pi 4 based set-top box software with IR handset remote control designed specifically for receiving narrow band DATV signals.

For more details see this wiki page:Ryde Receiver

Opentuner

PC based software developed by Tom ZR6TG

For more details see this wiki page: OpenTuner

Portsdown

The BATC designed DATV transceiver system based on a Rpi 4 has a receiver which has been tested and decodes the HAMTV signal

For more details see this wiki page The_Portsdown_DATV_transceiver_system#Portsdown_DATV_receiver

MiniTiouner

The MiniTiouner software is still available however the author F6DZP is no longer involved in the amateur radio community so is not providing support or enhancements and you can no longer register on the Viva DATV forum to download the software.

PC software receivers

SDR Angel is PC software that receives DATV signals using SDR hardware such as the ADALM Pluto and Hack RF - at this time we do not have any experience of using SDR Angel to receive HamTV. For more details see https://www.sdrangel.org/

Do note that any software-based receiver is likely to be several dB less sensitive than a hardware receiver, and will require a significantly more powerful computer.

Receiving the Signal

First - always check the HamTV transmitter status before attempting to align your system as it is unlikely that it will be left on 24/7 and it certainly will not be available when EVAs (space walks) and docking of space craft are happening.

It is likely but not confirmed that the status will be published on the ARISS international website and Twitter account – the ISSfanclub website may also have the status updates.

https://www.amsat.org/status/

Testing your system

As the ISS is only above your horizon for short periods, it will be difficult to see if your HAMTV receive system is working.

There are a number of tests you can do to ensure your system is optimised before HAMTV comes back on the air.

Measuring sun noise

The most useful is to measure the sun noise received on your system. This will not only measure your system performance but if you leave it running for a few hours with your rotator control system set to track the sun, it will confirm the accuracy of your tracking system.

Portsdown DATV test system

The Portsdown DATV transceiver incorporates a test function that has a continuous noise measurement facility designed to measure sun noise. It is very easy to use. Simply connect the signal from your LNA to the rx port on a Lime SDR and run the software.

For more details see this wiki page https://wiki.batc.org.uk/Portsdown_Noise_Meter

SDR continuum mode

Measuring sun noise can be done using SDR software running in continuum mode and running a program such as spectra view on the audio output – a Google search for sun noise measurement will show several techniques.

MiniTiouner Noise power measurement

F6DZP developed a suite of programs to help test a HamTV receive system which included a Noise Power Measurement program (see CQ-TV253 page 27 for more details). This was available as part of the MiniTiouner v0.8 package but appears to have been dropped in later releases. The program can be used to measure the noise power received by a Serit 4334 tuner over a period of time and requires no extra software or equipment to make sun noise measurements – the picture shows the sun noise recording from a RFHams 1.2 m mesh dish used to receive HamTV for the Principia mission in 2016.

Decoding a local signal

Once you have checked your system sun noise and tracking accuracy it is worth testing your system can receive a locally generated 2Ms DVB-S signal on 2395 MHz.

You can use the Portsdown Pi4 based system with a Lime SDR to generate this signal.

If you have an SDR capable of transmitting IQ files, there are a couple of small on-air HamTV RF recordings from 2016 that you can use for local playback: live.ariss.org/media/HAMTV Recordings/IQ Files/

• 5Ms/s Complex Samples
• WAV (SDRsharp) format
• Please note that these were recorded on a 0.6m hand-steered dish, so the signal in the recordings will fade in and out of being decodable even with the best receiver!

If these tests are successful you should be set to receive HamTV!

Actually receiving HamTV

All that remains is to wait until it is confirmed that the HamTV transmitter has been turned on then set your tracking program to follow the ISS and wait for the magic signs on the spectrum display (BandViewer?) or lock indicator that you are receiving the signal!

Once you have successfully received the HamTV transmission, the Dsave button in MiniTioune can be used to record data such as RF level, MER and Vber to show how well and for how long you received the pass.

BATC TS (transport stream) merger system

Once HamTV is active from ISS, BATC will be running the TS merger system. This is a server which combines the MPEG-TS UDP outputs from several ground stations and enables continuous video stream from the ISS to be presented to the school, reducing the pressure on the school ground station.

Despite several large capable stations in the system, ground-station-specific blockage is common on the ISS due to docked spacecraft and other equipment, so more geographically-diverse smaller stations are always wanted.

Once you have your system up and running please post on the BATC forum asking for more details.