Interruption of DVB -T television reception

Technical, legal and relational solutions to the problem TVI (Interference from television reception by amateur radio broadcasting) has been described many times in radio amateur literature in the past decades. For example, these are links [1,2,3,4,5], listed at the end of this article. Now, with the start of regular digital terrestrial TV broadcasting DVB -T (Digital Video Broadcasting – Terrestrial), the problem has changed somewhat, although of course the basic principles of suppression remain the same.

Who cares about DVB-T details, I recommend reading the book by Martin Legína [6]. A practical comparison of reception of terrestrial analog and digital television can be found, for example, in. on the website according to the link [7].

TVI problem – interference with television reception

I solved the newly created problem with TVI in mine 2. QTH, at a cottage in the Brda forests. Problems with TVI, which I previously had in the shortwave field [8] on the first day of November of this year, as i hope, will definitely end. On that day, analogue broadcasting is planned to be turned off - and especially so 1. a 7. television (TV) channel, on the Prague transmitter (Middle Bohemia) – Sugar. The reason for the end of problems with TVI from shortwave amateur bands is primarily the sufficient frequency separation of shortwave and IV. a V. TV channels. These high-frequency TV bands are also preferentially used for DVB-T. I recently had a problem with TVI, when did I start disturbing myself /respectively my wife/ ("disintegration" of the digital TV signal - "stiff" cubes on the TV screen and the disappearance of sound) when operating in the band 144 MHz. I receive DVB-T from TV transmitter Prague (Middle Bohemia) – Candy on 41, 53, a 59 channel. It is now a total 11 TV programs in digital quality (two private and one public multiplex).

Antenna for TV band

I use a broadband directional antenna, typ 10RD45F, with a medium gain of approx. 10dB and a TEROZ preamplifier for IV. a V. amazing TV, with a gain of 22dB. Because I have the TV transmitter Cukrák in the radio shadow (behind the hill), I had to, unfortunately, use this preamplifier. Solid professional companies, which deal with the installation of DVB-T for television viewers, they don't use preamplifiers (the possibility of intermodulation, etc.), if, however, it is possible in the given place.

Transmitting antenna for the band 2 meter DK7ZB

My transmit antenna for the band 2 meter DK7ZB (7 elements) it is placed on a lattice mast and rod with a rotator, approx 1,3 m above the aforementioned TV antenna. KTVI ("breakdown" of the digital TV signal) occurred when broadcasting in CW modes, SSB or FM in band 144 MHz, at transmission power from 5 do 100W (TRX IC746).

Cancellation

I basically did the cancellation classically, according to the block diagram in the figure. Here are some additional notes. The attenuator element is used to set the necessary amplification at the preamplifier location (so, in order to achieve reliable DVB-T reception, with allowance for poor income conditions – rain, snowfall). I had three attenuator cells at my disposal when setting up the suppression: 6, 10 a 12 dB/ 75 Ohm with F connectors (can be purchased e.g. at Servis-Elektro Praha, s.r.o.). Using an attenuator at the input of the preamplifier also "linearizes" it somewhat.

Band Retention

However, the most important suppression element is the band-stop for the band 2 meters with 35dB attenuation at 145MHz (supplied by DD Amtek Praha). The band-stop is originally intended for connection to the antenna input of the TV, therefore uses the so-called. IEC connectors. I had to use F connector reducers to install the suppression / IEC, connection (inserted IEC connectors) I then fixed it from the outside with pulled plastic tapes. The entire anti-interference chain is placed in a thin and long plastic bag and secured with adhesive tape. The whole is then put into a PET bottle (from Good Water) and attached to the lattice mast. After cutting the opening at the neck of the bottle, it naturally points downwards. The bottle is filled with mounting foam to protect against moisture (long-term properties of this solution - summer, winter - I have yet to try it).

The result of interference

Now I can broadcast in the band 144 MHz with power 100 W in every way and myself (DVB-T television reception) I don't disturb (perfect picture and sound), at a distance of TV and broadcast antenna approx 1,3 meters.

Links (References):

1. ing. Anton Mráz, OM0AAJ Jano, Grounding of broadcasting equipment not only in the block of flats, Radio journal 1/01
2. ing. Anton Mráz, OM0AAJ Jano, How to suppress TVI and BCI in our surroundings, Radio journal 2/01
3. František Dušek, OK1 WC, TVI doesn't just make a transmitter, Amateur Radio 1-2/03
4. Jan Litomisky, OK1XU, To the issue of TVI and BCI – 1999, website of the Czech Radio Club
5. http:/audiosystemsgroup.com (Jim Brown K9YC – Understanding and Solving RF Interference and Noice Problems)
6. Martin Legíň, "DVB-T television technology", BEN publishing house, Prague 2006
7. https://www.lupa.cz/clanky/srovnani-prijmu-analogove-a-digitalni-televize/
8. http://www.crk.cz/CZ/TVIDNC

Vasek, OK1DN
ok1dn@hotmail.com