TV Antenna

As all antenna designs are a compromise at some frequency, the trick is to work out what will give you the least compromise. To help get a broader understanding and hopefully clear up this confusion, Richard covers the basic types of antennas and their strong and weak points.
Created: April 2008
Latest Feedback: March 2016

Antenna Types

TV Reception is always an issue for caravanners. Unlike in most homes where TV antennas are professionally set up once and never moved again (unless moved by a storm or renovations), caravanners may have to retune every time they move. Therefore, selecting the best antenna for the job is paramount. Now there can be a lot of confusion with the many various shapes and designs of antennas as many have different performances at different frequencies. The basic types of antennas are:
  • Phased Array

  • Yagi

  • Omni-directional

  • Log-Periodic (including European models)

  • Tuned dipole
The theme presented for the modern caravanner is; the choice of antenna, the ways of tuning the antenna and some creative problem solving to ensure the best reception the antenna could possibly obtain. If TV entertainment whilst caravanning is important, then height and elevation may be helpful for better reception. A good idea is to choose an elevated campsite or provide extension solutions such as a piece of long pipe or some sort of telescopic device to gain extra height.

Phased Array

This is a common and popular UHF antenna because it covers the UHF channels 28 to 69 range of frequencies. By phased array, it is meant that two or more single antennas are connected in such a way that the signals independently collected are channelled together to make one signal. The result is an increase in signal strength. This setup generally has no directors in front (the smaller bars that extend forward on the Yagi antenna type) which makes them less frequency specific and therefore will work over a larger range of frequencies than a Yagi. They also tend to have a relatively even gain of signal across the whole range of UHF frequencies. This is important for digital signals and provides a very suitable antenna for caravans.

Yagi

This style of antenna when used for UHF does not cover the full range of UHF channels. A Yagi antenna has superior gain but limited bandwidth. In other words, it can be purchased for a group of channels only. For example, channels 28 to 38 is a typical group of channels a Yagi will cover. That means anything outside that channel range and performance will be poor. Therefore, it is not really appropriate for caravan use. You often hear a caravanner say they purchased a Yagi antenna and it worked great where it was purchased, but as soon as they move away from that area, it no longer worked as well.

Omni-directional

Using an Omni-directional antenna for caravanning would be highly unsatisfactory. This type of antenna was typically designed for marine use. These antennas, which are often covered in plastic, work well at sea because there are no obstacles to cause issues. Since there are many obstacles on land, these obstacles cause additional signals to be received by the antenna. These additional signals (either from behind or the side) may lead to ghosting or severe signal degradation of the incoming signal by the reflected signals. The signal can be so bad that the picture starts to break up, so for an antenna to work well - it must be directional. In circumstances where good results are achieved on a device like this, some would argue that a pair of rabbit ears with an amplifier would work just as well.

Log-Periodic

This style of antenna is quite good for caravan use because it’s very broadband (wide band of frequencies) and offers reasonable gain. The slight downside is there are usually too many elements poking out and this makes the antenna feel very big and awkward to carry. They also struggle on channels 0 to 5A because these antennas are not usually designed for this frequency range these days. Now with that said however, do not forget there are less than 70 transmitters out of a total of 3726 that are in this frequency range.

European Log-Periodic

The small European made log periodic antennas that are sold here can be a bit flimsy for Australian conditions and mechanically liable to getting the many rods caught and damaged when storing the antenna. However, with a suitable storage box made, it can be used successfully for caravanning. You will also need to add an amplifier to really make it suitable for caravan use.

Tuned dipole

This is a fairly common caravan antenna as these units are like an indoor rabbit ear, but mechanically designed for outside use. They are covered in PVC to hide the working bits and rely on harmonics to provide them with the range of channels they must pick up. This antenna is quite effective in good signal areas and very effective in weak signal areas where the dipole length suits the exact channel being transmitted.

The unfortunate downside is they are primarily made to suite channels 0 to 5A. They would do better if they added a UHF dipole and diplexed (a method of connecting a UHF and VHF antenna) them together to suit the situation today where 87% of signals are in UHF. The antenna’s performance varies from excellent to non-existent and so when travelling; it is generally limited in areas that have lower signal strength.

Testing

The way an antenna manufacturer would test a certain antenna model is by using a tuned dipole as a benchmark for comparison. They would measure the gain (usually in decibels or dB) of their antenna over the tuned dipole and work out how much extra signal their antenna is picking up.

When we say tuned dipole, what is meant is that the diameter and length of the element is designed for or ‘tuned’ for a specific frequency. So manufacturers would have a set of ‘tuned dipoles’, one for each frequency the antenna is being tested for. For instance, in many Australian capital cities, this would be one for each of the channels 7, 9, 10, SBS and the ABC. The manufacturer would measure the amount of signal strength their antenna achieves under the same conditions as the tuned dipole in a particular frequency. They may then plot these readings on a graph and take an average. This may be something like ‘8dB signal gain over the tuned dipole’ for example. A second method of testing is to give the signal gain when compared to a theoretical omni-directional single point antenna called an Isotropic antenna.

Solution

Since 87% of Australian transmitters are in the UHF range, the least amount of compromise would be to get an antenna that works best in this range. This would mean getting an antenna that covers the full range of UHF frequencies (channel 28 to 69) and an antenna that also provides reasonable gain. The best choice would be to consider a small phased array antenna.

For the VHF range you would choose an antenna that covers the frequencies mainly from 6 to 12 to make if sufficiently portable and to cover the largest range of transmitters. Since this range is less important, a simple dipole antenna with an amplifier should be adequate. For fringe area reception, a small log periodic antenna or a clever phased array antenna (likely to be larger) could be used.

Certain antennas are designed the way they are using a phased array UHF antenna and either a dipole antenna or a small log periodic for fringe area VHF reception. Usually added to this is a low noise built in amplifier (or booster) for even better results.

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