OH3TR

Tampereen teekkarien radiokerho
BOX 692
FIN-33101 Tampere, Finland
QRV 145,375 MHz
& 434,950 (-2,0) MHz
Tel. +358 40 952 6701

OH3TR Amateur Television Pages

Featuring the OH3RTR 1.2 GHz ATV Repeater in Tampere, Finland

This page is continuously under construction. We try to keep it as low in volume and as high as in content as we can. Mail us if you think you have constructive suggestions.

We'll get more descriptions of the local inventions here real soon now (believe it or not...), so please be patient and check in often...

Otherwise the pages are as is, enjoy! Link suggestions are welcome to the webmaster. Please let us know if you link us on your pages.


What is ATV?

Besides various other transmission modes, licensed amateur radio operators are allowed to communicate by using pictures. In the States, this mode is usually called ATV, for Amateur Television, in general. 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 is mostly used on the frequencies below 30 MHz, FSTV exclusively on the bands above 420 MHz. In Europe, 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.


OH3RTR ATV Repeater

The repeater was actually created out of opportunity, not of anything even close to long-sustained intention, something that has been typical for all OH3TR activity throughout the years. Some of the club members (OH3JGX, OH1LRY, OH3MRJ) had experimented with ATV in some occasions, like the Students' Union annual Club Exhibition that is held every autumn to help the first year students choose some activities for their spare time, a commodity that gets more and more rare every year. Then, some time in late 1994, we started to fill out application forms for an ATV repeater license, as our contest QTH seemed to be an ideal site for such an experiment. Soon OH1LRY managed to acquire a Nokia OEM version of the Kyodo KG110 UHF PMR repeater set from a surplus auction at OH2AA, and suddenly there was a widely accepted need for a 70 cm phone repeater, too. Someone thought that a 50 MHz repeater would be a nice addition to the local variety, and after some fast thinking (a very rare phenomen at our club, indeed) a common license was applied for all three. The TAC licensed the system under callsign OH3RTR.

The 70 cm speech repeater was the first to come on the air in July 1995.

Then we managed to find a suitable setup for the 6 m speech repeater, too. It came on the air the 3rd of March 1996. We would like to thank especially RATS and Arto, OH2BGN/OH6GJ, for salvaging the Kyodo KG110 80 MHz and 450 MHz units from a junk load at his work and selling them us for a reasonable price.

Suddenly a pair of commercial OB link IF stages became available through Michael, OH2AUE, one of the Finnish microwave and ATV pioneers. Those were the days when a good project still could gather enough people together to get it also finished. The ATV repeater came on the air in January, 1997. In the summer of 2004 a power amplifier and new antennas were added.


Basic parameters

  • QTH Hervanta water tower, Tampere, Finland, KP11VK
  • RX frequency 1282.000 MHz
  • TX frequency 1252.000 MHz

    The split was designed to be this way to avoid interference to the satellite and weak signal bands at 1269 and 1296 MHz). Now it seems that we are going to be very badly susceptible to interference from the wind shear profiler radars that are going to share the 1270-1295 MHz band with us.

  • 80 W ERP
  • FM modulation, -40 dBc BW 16 MHz

Transmitter (1252.000 MHz)

  • NEC OB link 70 MHz IF stage taken from an obsolete link transmitter
  • KK7B no-tune transverter to 1252 MHz
  • Mitsubishi M57762 driver stage, about 5 W out
  • One module from a Tecnomen PA930/125 with conservative backoff, about 40 W out
  • 4 dBd Alford slot, 55 m agl

Receiver (1282.000 MHz)

  • 4 dBd Alford slot, 67 m agl
  • MGF1302 preamp by OH3MCK
  • KK7B no-tune converter to 70 MHz
  • NEC OB link 70 MHz IF stage taken from an obsolete link receiver

Control

  • sync detector by OH1LRY
  • test pattern and callsign generator with a Sinclair QL by OH3MWY (we are planning to replace it with a Linux machine in the future to make remote programming possible and to get more versatile control functions)

So far, so good?

No, it took us a whole year to cure some basic problems.

First, the transmitter was blocking the reception badly, although the RX and TX antennas were separated vertically by some 12 metres, and there were interdigital filters both between the RX antenna and the preamp and between the driver and the PA. The latter configuration proved not to work well for wideband FM, although a similar solution has worked flawlessly for years in the OH3RNE 23 cm speech repeater. The official speculation is that the ripple of the filter before the PA introduced some PM-AM conversion in the wideband FM TV signal. Then the AM component generated intermodulation products in the PA, and some of the products falled in the RX band. We installed yet another interdigital filter, this time between the PA and the antenna, and the problem was solved.

Then there was a image rejection problem in the RX mixing process which led to a considerably less sensitive receiver than we had calculated. The transmitter signal was mixed to 40 MHz and the filtering in the NEC IF stage let some of the energy through. That was taken care of by inserting a 40 MHz notch in the 70 MHz IF line.

Even after these improvements the transmitter still affected reception. After some tedious investigations in the usual Nordic winter weather it was found out that the shield of the RG-213 cable between the preamp and the receiver was broken. The cable was replaced with a length of Nokia RF 1/2"-50 (now NK Communications Ohmax 1/2"-50), and finally the receiver system started to work all right.

The first version of the sync detector did have a tendency to detect sync right out of pure noise. The current one doesn't, although the sync detect threshold is far below the recognizable picture information level.

The NEC 7.5 MHz sound carrier modulator did a good job in reproducing the 70 cm repeater audio so that users with only RX equipment for ATV could comment the roundtables. Unfortunately its filtering stages also almost blocked out the 6.5 MHz sound carrier that is standard with the users so the modulator was switched off.

We have also had our share of ordinary hardware problems.

The Mitsubishi PA module was originally installed outdoors in a diecast box right under the TX antenna. It worked OK during the winter. Some time in the summer when the ambient temperature was at 30°C and the sun was shining directly on the heat sink, the module broke down. We bought a new module, increased the size of the heat sink by about a factor of 4 and installed the PA unit indoors in the cabinet with all other repeater equipment.

The original short circuit protection in the power supply tended to trip with no apparent reason. We had to ascend the water tower several times in a week at its worst to press the reset button. A new more robust construction has proved successful with no power supply problems since it was installed.

This is what the block diagram of the current configuration looks like.

We have been received more than 20 kilometres away. The sociogeography of the town tends to keep the most active users in the vicinity of the repeater (and thus within a walking/cycling distance from the university and the high-tech companies :-)), so we are still waiting for even some moderate DX.


Some picks direct out of(f) the air

We give you the opportunity to see some of our users live. Unlike the people you can see in the US or UK ATV captures, all of us are really under 40. Amazing, isn't it?

Here are some video shots from the repeater taken at OH3LDL.

  • Test pattern 800x600x24bit (77 k)
  • Test pattern 1600x1200x24bit (240 k)
  • OH3MCK 800x600x24bit (99 k)
  • OH3MCK MPEG1-stream 600kbit/s. 512kbit/s picture, 96kbit/s voice (Layer2), 44kHz voice (16bit mono). ATTENTION! The size of the file is about 10MB...
  • OH1LRY MPEG1-stream 1.5Mbit/s. 1.15Mbit/s picture, 224kbit/s voice (Layer2), 44kHz voice (16bit stereo).ATTENTION! The size of the file is about 50MB (VideoCD standard)!

Get a MPEG player for Win32 here.


Some local ATV inventions


OH3TR ATV Links

We have collected some links to other sites, especially to ones with technology oriented ATV information, but also to some club pages with impressive ATV repeater systems and other information we found useful.

ATV Technology Links

ATV Hardware pages by DL4EBJ. Various TX and RX projects, a 1,3 GHz 20 W power amp, antennas, a sync detector etc.

Amateur Television and high speed data signalling (F4DAY). Construction project for ATV and high speed data transmission.

S51KQ pages. A 68010-based ATV repeater controller, video generators, other ATV equipment, also kits available. Lots of other technical ham stuff like repeater controllers and paging equipment.

ATV Repeaters

PI6ALK 13 cm ATV repeater in Holland with live video and audio. Now also on satellite!

PI6ATV repeater pages, with some schematics and software.

DB0HEX, a German ATV repeater high in the Harz Mountains

The Stanford U Radio Club W6YX ATV Repeater. A quite formidable system that has been around long before us.

Microwave Experimenters Television System. KC6CCC twins in Southern California.

Mount Harrison ATV Repeater operated by K6ZVA in Idaho.

Tampa Bay Amateur Television Society repeater. Also some reference material.

Utah ATV Home Page, lots of technical ATV notes and an interesting overview of an in-band 70 cm VSB repeater.

ATV Experiments

Night Flight at 439 MHz, airborne ATV by WB9NEQ.

Aerocam, a 1250 MHz airborne FM-ATV system by VK1TMG.

Halo Rocket Balloon with ATV on board.

ATV Clubs and Groups

Amateur Television in Central Ohio (ATCO), interesting newsletters and a comprehensive link collection

Amateur Television of North America. A wide area ATV interest club.

Amateur Television in Pittsburgh. An overwiev of the ATV systems in Pennsylvania.

Amateur Television Network. Impressive linked ATV systems in Central and Southern California.

ATVA, Argentina Television Amateur Group

Australian Amateur Television Club. See how they do it Down Under.

Baltimore Radio Amateur Television Society. Also some tehnical information, mostly on 70 cm VSB NTSC systems.

British Amateur Television Club. The great-grandmother of all ATV organisations. See their CQ-TV Magazine online.

Brookdale Amateur Television System. Some interesting radiation pattern measurements and simulations.

Canadian ATV Links by VE4TV. Over 100 links to ATV sites all over the world.

Detroit Amateur Television Society. Bells, whistles and amazing remote surveillance and control experiments with ATV.

German Amateur Television Society (AGAF). Lots of ATV information (in German). Contents of their TV-Amateur magazine since 1969.

Niederrhein ATV pages by DL4EBJ. Nice co-operation between the German and Dutch hams at the border area near Cologne with the PI6ANH ATV repeater project.

Oregon Amateur Television Association. Lots of links, especially to the US ATV groups.

Regina Amateur Radio Television (VE5RTV). A good emergency oriented insight to ATV.

Slovenian ATV Team. Information about Slovenian ATV repeaters and contests, lots of links.

Swiss ATV. Most information is in French or German but there are lots of interesting links to ATV pages both in Switzerland and abroad.

Utah ATV Home Page by KA7OEI. Lots of interesting experiments ang good links.

DARC links about amateur TV

The ATV and SSTV links at dxer.com are a good source for information about radio amateur TV operating

Triangle ATV Association, an ATV club in North Carolina USA.

ATV Publications

Amateur Television Quarterly published by Harlan Technologies. Also an ATV search engine on the page.

Repeater, a Dutch ATV Magazine.

ATV Equipment Manufacturers and Retailers

G1MFG.com, "Home of the cheapest synthesised ATV transmitters and receivers in Europe"

Klein electronic (DL1IE), ATV equipment from Germany

Mini-Kits (VK5EME) has a comprehensive selection of ATV kits and other VHF/UHF/Microwave stuff, too

RSE Electronics in Belgium has a comprehensive range of ATV kits and equipment.

SSB-Electronic sells RSE ATV kits and components

Wyzcom (GI0UZG) has a comprehensive selection of ATV equipment

 

Just wait, your page will be here next! Keep us informed!

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Last updated: Saturday, 05-Nov-2011 20:24:06 EET