Software based DATV

ATV controller

ATV Modulator

ATV Receiver

Linear Repeater

On-screen video display

PIC Colour bar pattern generator

Building and designing an ATV repeater

The DATV Data Repeater

Digital ATV testing with COFDM (DVB-T)

RF to Optical

Repeater layouts

Video processing

Other projects
Projects
Introduction

Besides various other transmission modes, licensed amateur radio operators are allowed to communicate by using pictures. This mode is usually called ATV for Amateur Television or Ham Television. The two most common ATV modes are SSTV (Slow Scan Television), where still images are transmitted in normal communications audio bandwidth and FSTV (Fast Scan Television) where normal live TV video is transmitted in a bandwidth of several Megahertz to tens of Megahertz. SSTV/NBTV is mostly used on the frequencies below 30 MHz, FSTV exclusively on the bands above 615 MHz (50 cm band). Radio amateurs usually use the general expression ATV for fast scan TV on the UHF and microwave bands. This is where our amateur television activities are focused. Modern day ATV can be in the form of analog or digital transmissions. ATV is one area in Ham radio today where we are at the cutting edge of technology and thinking.

This web-site covers 20 years of projects mostly ATV related, but there is a few others here as well. I have tryed to break these pages into parts consisting of text, diagrams and photos. In this way I hope this is in a form that is easier to understand. This subject of ATV is an area in the hobby where I keep coming up with concepts and ideas to experiment with. This is where the enjoyment comes from, pushing the limits of this technology and seen how far I can take it.

History of ATV in New Zealand

The history of channel 39 goes like this; the band came about from changes in the Amateur 70 cm band at the time it was 420 to 450 MHz. The lower 10 MHz was removed for commercial use, in return the Amateurs got access to unused UHF TV band, we ended up with 10 MHz of space between 610 to 620 MHz. Back at the start of 1980 when this all happened there was air traffic radar in this part of the spectrum up and down the country. This made this part of the UHF unusable for commercial television. This was what it was like up to the late 1980's. When the New Zealand Government decided to go with the UK UHF television band plan. This involved 8 MHz channels that went from 502 MHz (channel 25) up to 814 MHz (channel 63) at the same time our 50 cm band was shifted to channel 39 between 614 to 622 MHz. Also the air traffic radar systems were upgraded and moved up to 1310 and 1250 MHz making this block of UHF channels around channel 39 commercially viable. With pay TV making use of most of the UHF channels commercially and local TV stations needed more spectrum for their services. The other problem we have encountered over the last 30 years is the loss of 420 to 430 MHz and 20 after that we lost 440 to 450 MHz with no new replacement spectrum provided. In early 1990's we also lost the usable part of the 13 cm band from 2300 to 2396 MHz now left with so much WiFi interference this band is unusable in build up areas.

At this stage all current ATV repeaters need to change over to the new digital platform at the same time as TV broadcasters do in 2013. The transmission standard we have been given is the DVB-T mode (COFDM 8k). Part of this proposed is the new VHF 5 meter band from 54 to 68 MHz. This will make a good ATV DX band to be used with any mode up to 14MHz wide. Plans already been put in place for a narrow FMTV DX mode to work in with 23cm IF up-converters. As for the new a DATV TV channel we have access to a new band (60cm) between 502 to 510MHz (E25). This will give as the freedom to use any type of modulation we like within the DVB-T/T2 transmission formats.

Auckland ATV Repeaters

Auckland ATV repeaters uses FM inputs and outputs to provide the best signal to noise performance, this is why the 70 cm band is no longer use for this reason. With the change to FM we now use dual sound sub-carriers at 6 and 6.5 MHz for stereo transmission. With deviation of 2.4 MHz giving a total bandwidth of 18 MHz. The 23 cm band has two frequencies set a side for ATV experimentation one at 1250 and the other at 1284 MHz.

The Nihotupu ATV repeater is located on the western side of the city has three 23 cm inputs where by two are FM and the other is digital (DVB-S) using QPSK modulation. With the output now on to the new 60cm band (channel 25 UHF).

The Whitford ATV repeater is located on the eastern side of city and relays the signal from the Nihotupu site. This repeater operates as a 23 cm in-band repeater again using FM for both the input and it's output.

Auckland ATV reflector

For updated ATV activity checkout Yahoo groups under the name of akatv.
Copyright © 2014 by Grant ZL1WTT  •   All Rights reserved   •   zl1wtt1@yahoo.com.au
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