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TV Aerials For Canal Boats and Caravans

Subjects are listed on this page in the following order :

The Particular problems of Boat / Caravan TV reception

Aerial Recommendations for Boat / Caravan TV reception

Maximising your TV picture quality on a Boat / Caravan   (including a worked example)

The Particular Problems of Boat / Caravan TV Reception

Since any aerial used for reception on a boat or caravan is usually required to work at different locations it is a given that a wideband aerial is required, with all the inherent disadvantages that this can bring in poor signal locations, particularly for A group,

B group and K group transmitters. Much as I dislike wideband aerials (wideband Yagis anyway) it must be admitted that the requirement for one is the least of the problems for

a boater, or caravaner. Many sites are in poor locations, especially for boaters as waterways tend to be in valleys ! (see Importance of Line of Sight). Furthermore space,

for storage of the aerial, is usually at a premium on a boat or in a caravan, so an aerial

of large physical size is problematic. Unfortunately, as a general rule, larger aerials give

more gain (i.e. more signal) and smaller ones less gain. Just using an aerial amplifier

to “boost” the signal from a low gain antenna is unlikely to be effective. I certainly found this to be my general experience, particularly when used with an Omni directional aerial.

Since the aerial is being put up and taken down regularly it needs to be pretty strong as well, I`ve seen some which are literally falling apart, though they`ll probably still give a decent picture in good reception areas !

Speaking of the latter, it is important to understand that the range of possible signal strengths available in this country is HUGE, see article on this subject.  

The fact a large aerial is out of the question is probably a blessing in disguise, because it is highly doubtful that the mounting for it would be strong enough to withstand a strong wind anyway ! On the subject of bracketry and poles, that`s another problem, because

aerials should be mounted as high as possible (particularly in poor reception locations)

and it`s doubtful that the average boat owner / caravan owner wants a 20ft mast bolted

to the side of their pride and joy. That said, a lot have satellite dishes, and they`re hardly aesthetically pleasing either, especially on a canal boat......

Actually all of the above is only the start of it, the biggest problem is that getting the best signal involves juggling with not one, not two, but three variables :

1 The direction of the transmitter is the most obvious variable, your aerial must be pointing at it (unless you`re right next to a main transmitter ! ) or your picture will be poor.

2 The tuning of the transmitter(s) which you`re trying to receive. Even if you`re right next to Emley Moor your screen will be just a snowstorm if your set is not tuned into it !

3 The third variable is often overlooked, and that is the polarity of the transmitter(s).

Get the wrong polarity and you could be losing up to 90% (or more) of your signal.

See Maximising Picture Quality

Aerial Recommendations for Boat / Caravan TV reception

It is possible to eliminate two of the variables mentioned above, namely direction and polarity considerations, by using an omnidirectional or “Omni” aerial.

The problem with this strategy is, how can I put this, Omni aerials are c**p.

The gain of an Omni must be negative (an Omni directional FM aerial is minus three dB) but that`s without taking into account the additional loss of signal that results in an incorrectly polarised antenna. Furthermore their beam width, to eliminate unwanted signals, is , well , zero !

If you get a good picture off an Omni TV aerial it`s because you`re in a good signal area anyway, I reckon that a coat hanger would work just as well.

I have always said that Omni directional TV aerials can`t be any good, but that was a theoretical position until we hired a boat which came with one and, much to the annoyance of my wife, I was able to make direct comparisons between an Omni and the aerial I recommend for touring, a DM Log Periodic. I`m a fan of Log Periodic aerials and this model is well suited to the role of touring. It`s reasonably compact (2ft 9in long)

bearing in mind that you never get anything for nothing, all things being equal a smaller aerial will give you less gain / signal. In addition it`s pretty strongly constructed and eminently fixable if it is broken as it`s nearly all metal in it`s construction.

At a conservative estimate its gain would be about 6 to 7 dB and since we use it as a control aerial for all our antenna testing its relative gain to all our other aerials can be

seen on the relevant graphs.

The big problem with a directional aerial over an Omni is it usually requires quite a bit more effort to get a TV picture. The thing is that the end result is nearly always better, as with so much of life, minimum effort = minimum result (and minimum satisfaction......)

So how much difference was there between the Omni aerial and the DM Log ?

I compared the signals on analogue and digital at two different locations and at different times of the day, on all tests the Log outperformed the Omni, as expected. It should be pointed out that detecting small differences in the aerials performance was made more difficult by the fact that the TV was an LCD, with their inherent picture inferiority over a CRT.

Below is typical result for a reasonable signal area on analogue transmissions, this was

off Moel Y Parc transmitter. Further down is a test in a poor signal area.  

Channel

BBC1

BBC2

ITV

C4 / S4C

Omni directional TV aerial

A bit grainy (worse than the Log)

A bit grainy (worse than the Log)

Grainy, fairly bad patterning and ghosting, interference lines on LHS

A bit grainy (worse than the Log)

DM Log Periodic TV aerial

Slightly grainy

Slightly grainy

Almost perfect picture  ! ? !

Slightly grainy

Notes    

To a TV engineer there is no such thing as a perfect picture, especially on an LCD or plasma....

It must be admitted that to get such good pictures off an aerial (any aerial....) mounted on the roof of a canal boat, it must have been a pretty good signal area. I wouldn`t expect this to be the case at most sites. However this throws into sharp focus how poor the Omni

was, by producing such a poor ITV. I was actually quite surprised and had to keep

swapping between the two aerials to confirm that this was in fact the case.

A more rigorous test was on the digital channels in the morning mist. The Log picked up all the Freeview programmes (that I could be bothered to check) with no problems, though

it must be admitted that all digital channels can block / freeze sporadically, no matter how good the signal. That`s due to skimping (by the broadcasters) on the error correction data,

i.e. trying to cram too many channels into the available bandwidth, see digital negatives.

The Omni failed to pick up half of the digital channels or was blocking in an annoying fashion, I wouldn`t have put up with it had I actually wanted to watch the programme...

That said, it performed significantly better than this the previous night in the different

weather conditions prevailing at the time. Then it was picking up most (but not all) of the channels OK, though the signal levels / quality were about 40% lower than with the Log.

Not that I would fully trust those figures anyway, how can they be that accurate when a digital meter costs £1000 plus, and the average set top box costs £30 !

We also spent a night moored up at the foot of the Bosley locks and I automatically

went onto Winter Hill transmitter (to the NNW) as every one else was on it !

I subsequently discovered that Moel Y Parc transmitter (to the West) produced better results, but some examples of the pictures off Winter Hill are shown below to illustrate

what one can expect to receive in a poor signal area..

Above we have BBC1 on the left and the text off ITV (i.e. none) on the right from an Omni,

and below we have the same off a DM Log.

The BBC1 picture off the DM Log is not as good as it looks in the photo, it was a bit grainy, but it was obviously far better than off the Omni.

Similarly there are a few Text glitches on the ITV text, but again, it`s a different ball game

to the Omnis non existent Text reception.

The site was the foot of Bosley Locks and the transmitter was Winter Hill.

Note the weather, not that pleasant for going through 12 locks.....

Maximising Your TV Picture Quality on a Boat / Caravan

The first thing to do if you want to maximise your picture quality from your TV aerial is

to avoid using an Omni directional antenna !  Well, sort of, explanations below......

As we have seen there are three variables to be overcome if one is to get the best

possible picture and, apart from local knowledge, there are two ways of achieving this.

The first involves research, knowing where all the transmitters are, their frequencies and what polarity they are. All this information is readily available but requires collating and remembering, or filing somewhere.....

For locations try our Transmitter Maps or the Digital Transmitter map or Ofcom Maps or MB21`s map page or BBC maps. For frequencies/ polarities try the last two.

Always bear in mind the over riding importance of “Line Of Sight” to the transmitter.

Even with all this info, unless it`s obvious which is the best transmitter to go for, it can sometimes a bit of effort and time when you actually moor up (or park up your caravan) to

ensure that you really are getting the best possible signal.

It is quite a satisfying achievement though !

There is another way of maximising you signal quality which avoids most of the above complication. I may not rate Omni aerials for actual reception, but they are bleedin`

handy when it comes to finding the best transmitter to use your other aerial on !  

How`s that then ?

Right, you moor up. You plug your Omni directional aerial in to you TV and scan right through the band, either manually or on “auto setup”. If by sheer good luck you get a

picture you`re happy with, you can just stick with the Omni for your nights viewing.

If you aren`t happy with the picture, select the channel with the best signal that the Omni has just found, then plug a decent aerial in, e.g. our DM Log. Now peak it up (direction and polarity wise) on that channel. Lastly, if necessary, tune all the other stations in. Done.

It may, or may not not be perfect, but it`s probably as good as you can get !

Worked Example of Using an Omni to Maximise Picture Quality

As mentioned above, we spent the first night at the foot of Bosley Locks, 4m NE of Cogleton. All of the other boats seemed to be on Winter Hill with their aerials pointing

NNW. Since there looked to be a reasonably clear “line of sight” in this direction I went

with it and it worked reasonably on the Log Periodic. The following morning I thought I`d experiment with the Omni and got the TV to do a search with it connected. Much to my surprise it was picking up a reasonable BBC1 on CH52 and BBC2 on CH45. Now I`d done

a bit of research on all the likely transmitters in this part of the world, but none had those programmes on those channels. I was intrigued. Referring to my trusty little BBC/ITC booklet “Television Transmitting Stations” (they don`t do it any more, you`ve got to print reams of A4 off the websites, such is “progress” ) I realised it must be Moel Y Parc !

I cranked the Log over to the West (Moel is the same polarity) and connected it up,

result, almost perfect pictures.

Apart from proving the usefulness of an Omni as a transmitter finder, it also underlined yet again how important “line of sight” is. Remember that Winter Hill was 34 miles away and kicks out 500kW (analogue), Moel Y Parc was 48 miles and only transmits at 100kW.

Gordon Bennet, an Omni TV aerial is smarter than I am, not good for the ego....

Below is an extract from our transmitter map showing Bosley, Moel Y Parc & Winter Hill