Saturday, 26 October 2013

Low-cost Amateur Digital Television- DVB-T ATV using UT-100C transmitter USB dongle




I am setting up a DVB-T tx on the atv channel on 70 cm. I am using a UT-100c USB dongle http://www.hides.com.tw/product_eng.html http://www.idealez.com/hides/product-detail/en_US/69859. It is only US$169 and produces 1 mW of DVB-T output. The software is at https://drive.google.com/folderview?id=0BzoVnSl8XNdQMmZPbDhEczA2RjA&usp=sharing. There are some pdfs of the device and how the software works.
 
To use the dongle, only the windows driver and PC2TV are needed. With PC2TV, only the video works at the moment. PC2TV takes a deal of setting up but will work with a PC/laptop webcam. 

Only the UT-100C dongle is needed to start. Some ordinary domestic DVB-T receivers can be used. The DVB-T channels in Australia are 7 MHz wide, the same as free to air TV.

As such, the standard Australian DVB-TV settings can be used. At 1 mW, it is possible to xmit on a free commercial channel and tune a TV to it, without causing any dramas. However, to work on the 70 cm channel, a TV dongle or set top box that can tune outside the normal free to air channels is needed. The cheapest and simplest way is to use a DVB-T receiver dongle (~$20)on the same PC as the xmitter; sounds bizarre but works. It is necessary to edit the channel parameters for the dongle, but that is relatively easy. 

The other person, I know of, using these TX dongles reports at http://www.oe7forum.at/viewtopic.php?f=7&t=410. It is German, but he has photos and web links. His work is also on the British ATV forum http://www.batc.org.uk/forum/viewtopic.php?f=15&t=3158 and http://forums.radioreference.com/amateur-radio-equipment/269047-dvb-t-70cm-23cm-2-3mhz-bw.html.

The Europeans are limited to a 2 MHz bandwidth, whereas we can use up to 7 MHz, hence their need for narrow bandwidth receivers (that are available from Hides). I bought the low bandwidth receiver ($80) but haven't used it.

In terms of other amateur DVB ATV activities:  

There is a long-running DVB ATV amateur project DATVexpress, a collaboration between amateurs in the USA and UK.  http://g4guo.blogspot.com.au/ http://datv-express.com/ (see technical articles for some of the background of DVB) http://www.w6ze.org/ (DTV section).

There are ATV groups in Brisbane  http://members.optusnet.com.au/~cardenrj/ and Melbourne http://www.vk3rtv.com/index.html. Both good for information.

Both have ATV repeaters. My aim is to access the Brisbane Repeater.

Currently I am trying to do (too many things at once):

1) Increase the power output, via a couple of Minikits amplifiers http://www.minikits.com.au/ . They are very good source of kits and bits. Also RF Shop   http://www.rfshop.com.au/. I have a Chinese generic 70 cm 50 W amplifier as the final. Although I was hooking them all up last night and found the Chinese amp has some weird thread on its UHF connectors. I pulled it to bits and can replace them with N connectors easily (I think). With TV, the amplifies can only run at about 10 % of their rated power. 

2) Setting up a better camera than a webam. I have changed from my laptop to my main station computer so I could install a HDMI camera input card (also does other analogue video inputs), an Avermedia DarkCrystal HD Capture Pro PCIE Card C027 ($100) from local Umart http://www.umart.com.au/newindex2.phtml?bid=4 .

I am using a cheap Canon camcorder HFR406 ($209) from JB Hi Fi. Somewhat surprisingly it worked quite easily, I think because I can use standard digital video ie 1080i or 720p in the PC2TV software. (Video formats drive me nuts).

3) Build a tilt-up mast, rotator and 2 m and 70 cm antenna. I am still setting up the basics of my station. Current status is mast is ready to tilt up, I have been waiting for concrete to set from a week ago. I have assembled all the bits to make the antenna (not simple to get). The design is per the ARRL Antenna book and uses insulated elements. It has been hard to source "top-hat" or stepped nylon washers and "push-nuts" for the insulated elements.

4) Playing around with studio software, to be able to have overlays (call sign) and switch between camera(s) and recordings. See http://www.vidblaster.com/. It has a virtual camera that can be the input to PC2TV. It is a commercial product but there are freeware ones around. They are mainly designed to stream to a network or record for YouTube, rather than direct to a TV xmitter.

5) Trying to get some basic test gear going. I have an interest in Software Defined Radio. I can use an RTL dongle SDR as a spectrum analyzer, but currently have limited bandwidth (3 MHz, whereas I need 8+). I am chasing some cheap Chinese gear that will give me spectrum and constellation plots. I need the test gear to monitor my amplifiers to start with, to avoid clipping/overload etc.

 

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