Digital aerials/antennas (often so called but read on) can be used in caravans or mobile homes. These TV Antennas/Aerials which are used by caravanners and truck (HGV) drivers (WVM) whenever they are in mobile situations will be different from the aeria/antenna you have on the outside of your house. Campervans and those with a laptop computer can also use portable or mobile TV antennas/aerials… but what type should you buy?

tv1This article looks at an antenna or aerial (they are the same thing?) for the travelling person, but reading it you will see enough to guide you regards your home digital TV aerial/antenna situation where you may need an antenna with a larger frequency range. However, don’t panic because the rule is wait and see. You will still get most channels if not all of them without an aerial/antenna change. If you are in digital range today don’t be concerned if you can’t receive the signal well enough for a picture because they are just about all on quite low power until the switch over for that area; this is to prevent interference on the present analogue channels.

The advice on this page will help you to make an educated choice. The writer has a class one Ham Radio licence and has made aerials/antennas for a varied range of frequencies to propagate locally and globally.

The first point I am going to make is don’t think that a higher cost for a portable (or fixed mobile) antenna means a good reception. In fact, sensibly speaking the opposite is in my experience essentially the truth.

The term broadband as used here has nothing to do with computer connections to the Internet; it is used in its technical sense to mean frequency coverage of all TV transmitters in the UK. The word broad meaning it can receive all the different frequencies (bands) that the ground TV transmitters use, it’s not just good for one of them.

Yagi

Some caravan owners have an antenna that looks like a herringbone with different element lengths. It is called a Yagi type antenna which often has 5 or 8 (even more) elements on the length of the boom, and these are excellent and are often fitted on a small mast and turned to point in the direction of a signal source. Mobile versions are broadband and will have a black bung in the boom end. Fixed home versions will have a different colours for the end bung depending on the transmitting antenna frequency. These are only suitable for receiving signals from some transmitters.

A small version yagi (table top) is excellent as is the yagi looking type, which is also very effective known as the log periodic in the table top condensed form. One of the two best antennas for limited space, these antennas (Log Perodic and Yagi) are what is known as broadband antennas in that they cover all transmitter frequencies in the UK (and possibly EU). Doing this all over coverage they are essentially not the best for receiving any specific one of the transmitters, but they are pretty good and unless you carry around quite a number of different antennas, each of slightly different dimensions, there is not another solution, so we will not labour that point any more. When it comes to digital transmissions you may find the odd area you stay in where a few channels are not too good, technically an even more broadband antenna is called for, but fear not you may never need to watch TV in an area where this might just be the case (but you can research this as time goes by). My advice is stick with what you have unless it is not providing you with a decent signal as and when it is required.

Don’t be concerned by the difference between a table top Yagi and a table top Log Periodic (table top or otherwise) for general use by all in the street. Forget the difference between these two and consider them the same, if they look like a sort of herring bone that’s enough.

Other Antenna

tv2Now to other types of commercial antenna available. You will see enclosed antennas in fancy covers, with fancy names, some with amplifiers to boost the signal. These may be different aerial types, but unless the covered enclosed antenna is a Yagi type (very rare if they even exist, I have not seen one) which is allowed to rotate, and should not be expensive or at least it has no technical reason to be expensive, I would suggest that you leave it alone.

Different manufacturers may produce the Yagi log periodic type in variants of shape, which is fine.

The flat panel antenna will generally be a quite expensive but technically cheap product so avoid them like the plague unless it gives you good technical data such as flat panel aray with a dbd gain of 9dbd or more. One of these if available to the general public will be very expensive because it must be produced to a very accurate standard and from a shopkeeper’s view nobody would want to pay that sort of money, especially when a Yagi or log periodic can do as well and in practice better due the cost difference. Even then a Yagi type will do better than the above gain for about £50 to £150 less so it’s no contest.

Many of these circular flat looking antennas are a simple loop antenna, some with pre-amplifier pretending to be grand, and have an relatively expensive price tag (£50 to £100 +++). If you have one of these fitted to your mobile home, caravan, or whatever, buy a table top portable antenna of the Yagi type mentioned and try this, positioned often by a window pointing at the transmitter or any big local buildings where reflections can occur, even sides of hills/mountains can produce a result. The point is a table top portable log periodic Yagi antenna (aerial) can be adjusted in an infinite number of ways, which includes moving the horizontal elements into vertical positions and any number of degrees in-between. Even walking around the mobile home can produce problems if the signal is weak so putting the aerial itself outside can be an answer, but read the following with care.

Don’t apply pressure to the wall of the coax cable as many are air spaced and ovulating the shape will reduce its efficiency. Make sure that a drip or water loop is made in the cable to cause all rain/water that might run down the cable to drip or drop off and not be allowed to follow the cable down to the appliance. The indoor table top antenna should be plastic bagged (perhaps doubled) to prevent any water ingress.

The above is a temporary solution that can be used if desperate and I mention it only to show what can be achieved if in that situation where you are otherwise proverbially stuffed, it being the sort of thing a radio ham might do, or technician. However, for an un-knowledgeable person unless you fully appreciate the caution required I really suggest you don’t try this, I repeat it is mentioned to show what can be done if you are fully aware of what you are getting into. For example, if vapour (longer term exposure) or water were to get on the antenna it can/could travel down the inner core into your appliance with terrible consequences.

I have only crossed the T’s & dotted the I’s of safety here and have excluded an explanation on vapour ingress if outside, even if specialist sealant can be used to vapour seal connections, I won’t go into this as it would not be generally needed, if only used outside occasionally and is fully protected.

So to sum up, with one antenna only, a Yagi or log periodic antenna is best (for your moving home situation) with its ability to move from its horizontal alignment to vertical as is required by circumstances. I apply this comment only to non domestic situations as fixed situations can be complex but because they are fixed, different solutions can be sought and often applied.

A normal outdoor antenna type Yagi is decent of course, but it must have a black bung in the antenna boom ends. All other colours are designed for specific transmitters and may be very poor with others, so black plastic boom bungs only if you are into caravanning and like a proper antenna, good luck!

antennastvTo the left are a few different antenna (aerial) types; it can be considered they are not for practical reasons used for domestic receiving purposes for the situation/s I am concerned with for this article. It should be noted that the odd transmitter might be vertically polarized, meaning your Yagi antenna needs to have its elements in the vertical position. As a matter of interest there is a massive amount of different configurations for antennas/aerials, and there is no point in mentioning them in this article, as they would be quite unsuitable. Many are for fixed situations and point to point communications.

Getting a few cheap suction cups from a hardware store and using a combination of plastic sticks (or thin very dry wood) and polypropylene type string (which gardeners use) can assist you in placing your antenna in an odd position in your truck cab or caravan if you find yourself in a borderline TV signal situation. The string or thin plastic will not essentially affect your antenna.

Vertical/horizontal Omni directional antennas are low gain and fine for areas where signal strength is very good. Omni directional Antennas (for these purposes) are for good signal strength areas only.

Cross Yagi antennas which can be electrically made to produce circular polarisation as a helical, (rotating magnetic field) but to any single degree either clockwise or anticlockwise. There is a small price to pay which is a little loss in efficiency.

Terms

An Isotropic (dbi) (the name is a reference point) antenna is an hypothetical antenna in free space (away from the earth in orbit if you like).

Dipole antenna (dbd) (is a sensible reference point) is a half wave antenna more often used as a benchmark (reference point), it is about 2.2db better than an isotropic antenna. To help you further, an antenna/aerial that gives its gain in dbi as say 5dbi is about the same as an antenna that says its gain is about 2 or 3dbd, given I would trust a rating from those who quote gain in dbd more than those who quote dbi, and then hide the dbi figure in small print if it’s there at all. We can argue that point but that’s my opinion. If you can’t discover the reference point for the gain don’t buy it.

dbi (the name is a reference point) gain means how much better this antenna is than an Isotropic.

dbd (is a reference point) gain means how much better this antenna is than a dipole which is a real antenna.

To help you appreciate more how an aerial works the word gain has been used. I will apply the same to a car’s headlights. If you remove the reflectors from a car’s headlights, then try and drive at night you will fail. All the light produced (and the power has not changed) goes all over the place, not where you want it All the reflectors do is direct all the light produced forward in a controlled cone shape, the result is quite remarkable I am sure you agree and yet we did not change the power of the lamps/bulbs. We call this Gain. An antenna is the same, we stop it listening (mainly) in all directions and direct it where we require it to listen (or transmit as is the case), the difference is we are dealing with magnetic waves of different lengths so we need to understand that subject and that can be complex.

db gain means the seller or manufacturer does not want you to know what the gain is reference to, but assume its dbi 100% and remove more than 2db from its figure against a antenna giving dbd. Also consider that if the claim is db for gain, which can only be designed to get some advantage which could be considered dishonest, should we then consider them suitable to receive our money in return for goods they have possibly sort to misrepresent.

Collinear Antenna – this could be okay but still a waste of effort as it needs to be quite long and then it looks (hears) in all directions at right angles essentially, so it’s not a practical contender for this job. A 5 to 8 element house type (size) Yagi (caravaners with storage space) is great for those who want practically to have a good chance of TV in most places, but not all. This coupled with a cheap omni or table top is fine.

Truck Drivers or WVM (white van man) would, as my preference, have a table top portable Yagi, log periodic.

Number of elements does not mean more gain as spacing between the elements is the most serious factor with antennas, however in the practical world we have to compromise.

Antennas are rather complicated and are a specialist subject, experience can be a great benefit for TV house antenna installers, but a very deep electrical knowledge is required to dig into the concepts of its design. Electromagnetic field distribution knowledge along/around the antenna and feed points is essential for design. I have written another page on this site for CB Radio (citizens band Radio) users if you have an interest in antennas for CB Radio.

Buying

After all this stuff most of which you didn’t want to know, you are thinking okay but what would you do, well the answer is not a surprise. I would use a table top antenna bought from say Maplins for less than £10. It would be a Yagi 4/5 elements or more, don’t worry about the fancy shapes some of the elements have on these antennas, just look for what seems robust enough to be sensible for you. Just the one antenna for all occasions, if that doesn’t work then any other aerial apart from an external one won’t succeed either. Don’t forget you can orientate this antenna in a multitude of different ways in a poor location where signals are bouncing all over the place and all of them quite weak, I won’t explain the reason for this, please just accept it. In some cases it’s quite common to point the antenna away from the transmitter to collect a sum of reflections and direct signals, but beware of moving around in your accommodation if this is the case as the signal can vary if you move.

Don’t be fooled into buying an expensive flashy looking antenna generally covered in beautifully shaped plastic with pretty symbols on it claiming to answer all problems and costing well over £50 and often £100 plus. These antennas may have applications in good or decent signal strength areas but outside that they are useless, they often boast an internal amplifier, but note this – when a signal is weak it will also have noise (unwanted content) included in the signal. An amplifier will simply amplify everything, including the unwanted noise and then add to that its own inherent noise level. To a fine point it’s fair to say you can improve matters with such amplifiers, but beware the result can also be rubbish! You may see antennas/aerials saying they are for DIGITAL SIGNALS, BEWARE BECAUSE TECHNICALLY THERE IS NO SUCH THING AS A DIGITAL or ANALOGUE TV ANTENNA/AERIAL. THE SIGNALS MAY BE TRANSMITTED ON A DIFFERENT FREQUENCY OR RANGE OF FREQUENCIES which may require a different antenna, but NOT because it’s digital, it would be simply because they have chosen to transmit the digital signals on a different frequency or frequency range.

IN 2010 more flat panel array antennas are becoming available, many are produced in other countries to a standard that is very suspect, due to the purchaser in the UK not paying for a decent quality controlled unit. China for, example, can produce first class goods if the importer wants that, with regret too often the importer wants the cheapest that looks good so it’s hit and miss if you get the performance you presume you paid for. This applies even more for WiFi antennas which have an even higher frequency requiring even more correct dimensions and each one requiring testing for its performance. My experience is that this may well not be forthcoming. Sad to say these can be called a product of our society where greed to make money and essentially (my personal words) con people is a priority. Make sure your supplier is honourable and will replace or refund your money if you are not satisfied.
Portable TV antennas are broadband for the range of TV transmissions offered at this time; fixed external antennas/aerials that have a black bung in the end are also broadband antennas and may not need changing. Indeed your present antenna may be suitable. DON’T get another unless you find difficulty with some channels, which will be because the NEW frequency range or frequencies for some stations are outside the remit of the antenna, but it will not be because it’s digital per se, it will be because the signal for a certain channel has moved too far away in frequency for this antenna. The proof of the antenna is simple: are you receiving ok?

Digital Broadcasting has many benefits including much better coverage from a given antenna transmission point, and at lower power giving green savings. Because much lower strength and quality signals can be made into a perfect (well near enough) image/sound your present antenna may be more than able to supply the signal for your receiver because the digi box can make good sense from a much weaker signal. No you don’t need a new TV, just a conversion box like the present freeview one – cheap as chips. Sky satellite viewers often don’t even bother to receive signals from ground stations, they get everything via satellite and for them nothing has changed! They need do nothing!

An option for non Sky viewers rather than bother with getting a signal from a ground station via your normal aerial roof installation, is get a Sky sat box and dish installation with a zero subscription viewing card from Sky, and this way you will get all your normal ground transmitter stations plus quite a few others. There may be other satellites in orbit that you can get transmissions from so investigate by all means, but the Sky sat is a sure way that has been available for years unknown to most of the general public. The total cost including installation is currently (April 2010) £175 which gives you a new Sky box and 240 channels. NO SUBSCRIPTION IS REQUIRED BUT A ONE OFF COST FOR THE CARD WHICH IS ABOUT £25 IN SEPTEMBER 2010. This can be set against the cost of a normal TV Aerial installation if you are in need of one, or it’s a chance to upgrade and get all the extra BBC and other channels with no subscription.