[amsat-bb] Upcoming HamTV ???
dan at post.com
Sat May 7 17:47:03 UTC 2016
> What are the chances that the HamTV transmitter will be active during the
> pass over the US? Do they turn the HamTV transmitter on early?
Yes they do. The camera is often connected and downlinking before and
after school contacts. It was on over Australia one time at least.
> Does anyone know which frequency and which mode will be selected on
2395Mhz Symbol Rate 2000. DVB-S QPSK. Note there is only one
recommended receiver. Other DVB-S receivers may or may not work. The
ideal way to test is to generate the EXACT same signal as the ISS (If
you can). There is also sample TS files online to test equipment, to
see if it works in the real world. 99% of the time there is no video,
but normally QPSK downlinking
> In the same vein, does anyone know of a good webpage or other
> resource for determining the operating schedule of the HamTV transmitter
> or is the upcoming contacts page on the ARISS site the best place?
There is the email list specific for HAMTV. In general live video is
currently only used for European direct or telebridge contacts as
Europe is the only place with a HAMTV ground network. There is plans
for similar networks in Australia and the USA. It has been picked up
in Japan too.
Nearly EVERY pass there is what we call "blank transmission" which is
the transmitter outputting QPSK modulated transport stream with the
stations name and video. However as the camera is not normally
connected, you receive black video, with a blue bar on the left side.
We would like a proper test card, but this is not possible at present.
However these blank transmissions are very useful for testing
tracking, and alignment. The recommended setup can log the signal
strength every 1 second, giving a very good idea of the performance of
> We recently got our 3.0m Dish and S-Band receiver systems installed in
> the VTGS and I was hoping to get up early Monday morning and attempt to
> record the HamTV transmission as ISS passes over the US on its way to
> the UK for the planned ARISS contact.
You can start now to attempt to receive the QPSK transmission. I
assume it is on, at least it was 2 days ago.
> Hopefully, if I can get a clean IQ
> recording of the HamTV transmission, we can use the recording to begin
> developing our GNU Radio DVB-S demodulators to extract the video stream.
There is a recommended set up, which is designed for decoding and
recording etc. If not using a recommended setup then it may be hard to
test that it will actually work when live video suddenly appears. For
example some receivers cannot do low symbol rates or are bad at doing
it. Other receivers need the channel "saved" before they will display
it. There is also a problem with the downlink format. While it is
"standard" DVB-S format, there is some non standard components in the
transports stream. This can cause receivers that work fine with DVB-S
to not display the video. The problem is missing tables which the
recommended software fixes automatically:
The best way to confirm your setup will work is to recreate the exact
same signal as from space and decode that.
In terms of tracking the ISS. Most European ground stations are using
modest 4ft dishes which have a wide beam width and make tracking less
critical. Larger dishes make tracking much harder especially at high
elevations where the ISS appears to move faster.
I would recommend
1) Use TLE files directly from space track (not from AMSAT) updated daily
2) Calibrate the dish using sun tracking or sun radio noise tracking
and confirm it is accurate.
3) If you have problems consider using the recommended hardware (DVB-S
receiver) and possibly a smaller dish. We also have special Wifi
blocking filters available.
Lastly we are looking for US ground stations to offer to receive HAMTV
for USA contacts. If you feel you could do this, then we can provide
more help with recommended hardware and support to help decode and
stream the live video. Ideally we would like a chain of stations
across the US for at least 10 minutes of constant overlapping video.
HAMTV Ground station in Ireland
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