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Old 30-12-2013, 07:40 PM   #559
mrsun18
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Join Date: May 2011
Posts: 2,809
Understanding Indoor Antenna

This post arises from numerous questions about indoor antenna.

To use an analogy, using antenna to capture tv signal is like fishing.

Kelong is located at the most advantages location to trap fish. The design is optimised to lead more fish to the net. Similarly, outdoor antenna is installed at the best location (roof top). The design of the antenna is optimised to capture VHF or UHF signal.

For UHF signal, the optimum length of the antenna element is about 0.25 to 0.3m for the Singapore DVB channels (half of 300 divided by frequency of channel in MHz). Those who have seen roof top antennae would have noticed that they are installed in a horizontal plane. This is because the signal is polarised in the horizontal plane. If the antenna is install in the vertical plane, signal received would be zero theorectically (think polarised as in sunglasses). [The relevance of this information will be clearer later]

For master tv antenna (matv) serving a large number of units, the signal is processed and amplified before distribution to individual units.

For UHF indoor antenna, reception is compromised because of obstructions from building, reflections, etc. Furthermore, sometimes it is smaller than the ideal dimension. However, this can be compensated some what by tuned circuit incorporated.

Nevertheless, the technology of DVB transmission has taken care of these limitations, more so in T2 over T format. With built-in error correction and only a small fraction of signal strenth required as compared to analogue tv, very weak signal still can be decoded successfully for perfect reception.

So, a simple rabbit antenna, or one as I have used and shown in the other post, can be used successfully. The important point to note is that indoor, the antenna element may not neccessarily be always in the horizontal plane. The antenna element may have to be inclined at 45 degree, for example. This is because refections of signal may have changed the polarisation. Effort may have to be made to find the best orientation and location for best overall reception. (This is also true for outdoor installation). Extension cable to increase the lenth of the cable may help to improve the chance of getting a good location.

Pic and more info contained in the other post:
Spoiler!
How about amplified antenna?

An "amplified antenna" is one that comes with a booster, either built-in or attached as a separate device. For indoor use, the booster is a small amplifier that can increase the signal strength received from the antenna. But as an active device, the booster also introduces some noise. So even if the signal strength is boosted, the signal quality may deteriorate.

As can be seen in earlier posts, results vary. Every case is unique. It pays to try various options.

Last edited by mrsun18; 30-12-2013 at 08:31 PM..
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