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Ever tried tuning your PAL or NTSC analogue TV antenna under poor coverage? Probably you would experience snow (noise) and ghost (multi-path signal reflection) by swinging the antenna from one side to another, and somehow you might be able to see something on the screen even if you are getting a poor reception. Digital TV, on the contrary, offers you everything or nothing. You'll get good picture if you can pick up a channel above a certain signal threshold, but no picture otherwise.

When people talks about Digital Terrestrial TV, DVB-T is not alone. Although it is mostly adopted by the European and Asian countries, there are also the Japanese ISDB-T and the American ATSC standards.

Digital TV broadcast is being on trial in some countries with full switchover expected by early next decade. There could be a phase during which analogue and digital TV could coexist but final switchover is the way to go. It might take a few more years before the households need to get a new  Digital TV decoder, TV set or possibly the TV antenna. Some of the benefits of the digital TV pictures are highlighted at the bottom of this page.

As the DTT trial is going on, the DVB-T USB dongle kit is probably more relevant to the road warriors who carry their laptops around. Many new and affordable digital TV receivers are hitting the market this summer. Most kits come with a USB dongle receiver, a +2dBi rubber duck antenna and a credit card sized remote control, as shown in a sample kit on the right. While these receivers work fine in open areas, the +2dBi rubber duck antenna might not be strong enough to maintain the digital signal reception under the roof even if you're sitting nearby the windows. Many users has asked for a handy and yet a stronger antenna to give an extra push to go beyond the signal threshold.

danets has launched the +5.5dBi DB-T omni antenna below to meet the increasing demand of the rubber duck replacement. It comes with a magnetic base that allows you to stick it on the roof of your vehicle and a 2 meters pigtail with various choices of matching RF connector for the USB receiver dongle termination.

+5.5dBi DVB-T Omni antenna with magnetic base improve signal reception for digital TV receiver 2ft pigtail with choice of RF connectors to fit in a wide variety of digital TV receivers Easy to stick to the car roof with magnetic base

Standard International Air Shipping Standard International + Insurance

+5.5dBi DVB-T Omni antenna. Please choose the RF connector on the right. IEC RP-SMA   US$14.95   Shipping US$6.5   Insurance US$1.95   MMCX MCX-male

    Packaging content:

    +5dBi DVB-T Omni antenna specifications:

    Digital Terrestrial TV standards:

DVB-T
The DVB-T standard, approved by the European Telecommunications Standards Institute (ETSI) in February 1997, is capable of supporting both Standard Definition Television (SDTV) and High Definition Television (HDTV) modes and is based on the Orthogonal Frequency Division Multiplexing (OFDM) technology which provides multi-path immunity to the receiving system. In this regard, features like mobile reception and the Single Frequency Network (SFN) configuration can be supported. The standard also provides different options on the use of modulation schemes and number of carriers. DVB-T standard specifies the use of Quadrature Phase Shift Keying (QPSK) and different levels of Quadrature Amplitude Modulation (QAM) in order to trade bit rates against robustness. For instance, the QPSK modulation is more robust against different fading conditions but offers small bit rates, whereas higher level of QAM provides more bit rates but is less robust. The standard also allows the choice between the 2k carrier mode which is suitable for relatively small single frequency networks with limited transmitter power, or the 8k mode which can be used for large area single frequency networks. In addition to the member countries of the European Union, other countries like Australia, India, New Zealand and Singapore have also adopted DVB-T as the Digital Terrestrial TV standard.

ISDB-T
The ISDB-T standard was developed by the Association of Radio Industries and Business (ARIB) and approved by the Ministry of Posts and Telecommunications (MPT) of Japan. It was first publicly demonstrated in November 1997. ISDB-T can support both the SDTV and HDTV modes. The standard is also based on the OFDM technology which improves the robustness against multi-path fading. Different modulation schemes such as QPSK, DQPSK, 16-QAM and 64-QAM are supported in the ISDB-T standard. Likewise mobile reception and the SFN configuration can also be supported.

ATSC
The ATSC standard was adopted by the Federal Communications Commission in December 1996 as the Digital Terrestrial TV (DTT) standard to be deployed in the United States. Subsequently, the DTT service has been launched since November 1998 and more than 50% of the American population now have access to DTT signals in around 120 cities of the United States.Argentina, Canada, South Korea and Taiwan have announced the adoption of the ATSC standard for the DTT service. The ASTC standard is capable of supporting high qualiy video, audio and ancillary data in both the SDTV and HDTV modes with the use of the Vestigal Sideband (VSB) modulation schemes.

    What are some of the benefits of Digital TV?

Below are some of the benefits of Digital TV highlighted from DVB-T, ISDB-T and ATSC system trials in Hong Kong (source: OFTA Hong Kong):

Improvement in reception
The performance of all three DDT systems (DVB-T, ISDB-T and ATSC) was much better than the existing PAL-I system with more stable picture and sound quality and more robust reception. The field trial demonstrated that the three DTT systems could help resolve the poor reception problems of the existing PAL-I television system. They also offer lower transmitter power compared with PAL-I.

Support of SDTV and HDTV
The three DTT systems were able to support both SDTV and HDTV in different reception conditions including fixed and indoor locations, and reception via the in-building coaxial cable distribution system (IBCCDS).

Support of mobile reception
Mobile reception of ISDB-T and DVB-T was good in open areas. The ATSC standard was not designed for mobile reception.

Compatibility of DTT signals with PAL-I TV transmission
Field measurements in fixed outdoor locations, in the system headends and TV outlets of the IBCCDS indicated that o adverse effect was caused to the reception of nearby PAL-I signals by the DTT signals. In general, the DTT signals were compatible with the PAL-I TV transmission network, whereas certain specific system alignment work would be required when DTT signals were distributed via some of the IBCCDS in Hong Kong.

Support of Single Frequency Network (SFN) configuration
Both ISDB-T and DVB-T supported SFN operations. The ATSC standard was not designed for operating in SFN configutation.

Effect of tidal fading
All three DTT systems were affected by the effect of tidal fading in similar fashsion as PAL-I. Precaution should be taken in aligning the receiving systems to avoid the sudden fading of the digital signals that drop the picture.

Protection ratios and overall encoding/ decoding delay
The protection ratios of co-channel interference, adjacent channel interference and image channel interference of the three DTT systems, and the overall encoding/ decoding delay of the ISDB-T and DVB-T systems were found to be consistent with the figures quoted in the respective standards.