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Aerial Pole and Bracket Tests

Poles & Brackets Tests

Our recommended aerial for boats and caravans, the DM Log Periodic, near Bosley locks

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 ?


Although analogue is no longer available it actually makes a better test of aerial performance because of the way the picture degrades compared to a digital signal.


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.


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

Note that to a TV engineer there is no such thing as a perfect picture, esp on an LCD TV...

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 trust the signal level readings on TVs (or £30 meters for that matter)…….


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.

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BBC1 analogue off an Omni aerial ITV teletext off an Omni aerial Analogue BBC1 off a DM Log aerial ITV teletext off a DM Log aerial

Above, via an Omni, we have BBC1 on the left and the text off ITV on the right.

Below we have the same off a DM Log

Note : neither analogue or Teletext is transmitted anymore, but for the purposes of aerial testing it is actually a superior indication of degrading signal quality than digital.

Our recommended aerial for boats and caravans, the DM Log Periodic. Canal boating holidays, expensive ?  But recommended.

Number One > if you want to maximise your TV signal avoid using an Omni directional aerial !


On the other hand, in my opinion, the best aerial for a caravan or canal boat is a DM Log Periodic and that is the one we use when we hire a boat.


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 may require 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`re sometimes bleedin` handy when it comes to finding the best transmitter to use your other aerial on !

How`s that then ?

Right, you moor up / park 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, be perfect, but it`s probably as good as you can get !

This method worked better with analogue signals but it`s still worth trying with digital ones.


If all else fails you could try one of those basic signal strength meters. Most professional installers would laugh at one of those because (regardless of any failing they may have in accuracy or sensitivity) they just give one reading for all  the received frequencies. However, this means that they`re actually very handy for finding the strongest source of TV signal for a boater or caravanner because they don`t actually know the frequencies !  Thus, because you don`t need to “tune in” cheapo signal strength meters you eliminate one of the three variables, though don`t forget you still need to check which polarisation is required. So to be sure you`ve covered that particular variable you may have to go through the whole signal finding process twice, once with your aerial horizontally polarised, and again with your aerial vertically polarised. Finally the strongest signal may not be the best quality but those cheap meters only check for signal strength.

Note : 4G transmissions can make cheap signal level meters worthless because the 4G signals are within the frequency band which the cheapo meter is looking for. It may report large signals in a particular direction but that might just be a 4G mobile phone mast ! You can get round this by using a filter between the aerial and the meter (we recommend a CH56 filter), though meters sold after summer 2013 may have built in filters, so check with your supplier.


I`m told you can get an I Phone “App” which can sometimes be helpful. Apparently your I Phone knows where you are so you just use this “App” and it tells you which direction the transmitter is in ! I have to say I think that`s pretty clever, though you must bear in mind that reception predictors are not always to be relied on……

Site




Ely (Nth of)


Stretham


St Neots

“Set Top” TV aerial (on the roof)


CHs 1 to 4       C5


Poor                 Virtually Nothing


Reasonable      Poor


Very Good        Reasonable

DM Log Periodic TV aerial


CHs 1 to 4         C5


Good                  Poor (but there ! )


Nearly Perfect    Good


Nearly Perfect    Nearly Perfect

In May 2009 we hired a cruiser on the River Great Ouse from Ely, which was more scenic than you`d think by the way, though the locks were busy on the Bank Holiday Monday !

Anyway the boat came with a set top type aerial but a reasonably good one, a small Log Periodic in fact. I took the opportunity to compare it to my DM Log and the results are summarised in the table below. I`ve split the results into CHs 1 to 4 and C5 because the latter was low power and had a restricted radiation pattern, therefore receiving it required a lot more from the aerial. I put the set top on the roof (when comparing them) and it worked reasonably at most sites because, let`s face it, it`s pretty flat and not that far from Sandy transmitter !  In fact when we moored up at St Neots we could see the Sandy, loud and proud on the horizon. Even the set top (including when actually on the set top ! ) gave a very good picture, thus explaining why some people think their Omnis are great. It`s all about signal strength, even an Omni inside the boat would have given a good picture there....

More problematic was when we were North of Ely (and in Cambridge) though Stretham was about mid way between the two, signal wise.

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 glitches on the ITV text, but again, it`s a different ball game to the Omni`s non existent Teletext 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.....

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Cable


Because the cable runs on boats/caravans are usually pretty short cable quality is not quite as important as it is with aerial installs on houses, but since the price difference is so small anyway it really is a false economy to use cheap crappy cable. “Low Loss” coaxial cable is not recommended, I`d always use decent quality satellite grade lead. It`s not so much for the difference in signal loss (which would be relatively small on the short runs), it`s more for the suppression of impulse noise which can be very annoying with digital pictures. It`s probably an even better idea to go for copper/copper type cable (as opposed to RG6) on a bost than it is on a house install because damp might be a problem and copper/copper is less susceptible to corrosion than alloy foil RG6 type cable.

Finally when it comes to cable colour it is often tempting to go for white but remember that it soon gets dirty, so I`d go for black myself !

TV Aerials For Caravans & Boats


Subjects are listed on this page in the following order :


The problems of Caravan / Boat TV reception  


Aerial recommendations for Caravan & Boats

incl : Omnidirectional TV aerials (not recommended) & the DM Log


Don`t forget your cable


Maximising your TV signal on a Caravan / Boat


Great mysteries of the world (part 579)


Post Switchover Post Scripts


How high to mount your aerial.......


Mounting Aerials :   On Boats     On Caravans


The satellite option


Tests of commonly used caravan / boat aerials

incl : What`s inside a Status TV aerial !

* A metal one, obviously......

** Many bomber command missions in the last war had appallingly high loss rates (of 5% or more).

The most efficient of the Japanese Kamikaze squadrons had a loss rate of 100%.

The aforementioned Italian Kamikaze squadron had a loss rate of around 0%.


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 fitted. Much to the annoyance of my wife, I was able to experiment as to the differences between an Omni and the aerial I recommend for touring, a DM Log Periodic (as also supplied in our caravan aerial kits), and unsurprisingly the Omni didn`t fare too well. I`m a fan of Log Periodics and this model is particularly well suited to the role of touring. It`s reasonably compact (3ft 6in long) bearing in mind that you never get anything for nothing, remember, all things being equal, a shorter aerial will give you less gain / signal and use of an amp (“booster”) does not compensate for this. We also stock a shorter version of the DM Log, the DM18 Log, so called because it only has 18 elements compared to the 26 of the “standard” DM Log. Thus the DM18 is only 2ft 6in long but, unfortunately, you will pay for that with slightly less gain, about 1dB less, so generally, unless you really need a shorter aerial, I`d go for the standard version.

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The DM Log can just about be seen to the left of my wife and my parents as they finish their wine outside in the dusk, in the perfect peace and quiet. The aerial is more clearly seen in the reflection on the water.  This is one of my favourite pictures (link) and if it doesn`t put you in the mood for boating, then nothing will......  This is why I`m a boater not a caravanner, except in New Zealand !


Inland Waterways Association              Reopen the Chesterfield Canal


Waterway clean ups / "litterpicks"


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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, compared with a grouped aerial. 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 caravanner. Many sites are in poor locations (especially for boaters as waterways tend to be in valleys ! see importance of line of sight) and 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 aerials give 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, but also, even more importantly, fixable. I`ve seen some aerials which are literally falling apart, though, somewhat surprisingly, they`d 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 the article on this subject).  

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We are more than willing to give advice to those actually purchasing from us. Could those only seeking information please just find the answer somewhere on this site, or ring an aerial installer local to them, or call the reception advice phone numbers.

Caravan / Boat Aerial Pole Installations


It`s all very well having your aerial(s) and knowing how to get the best of them, but how do you install the pole that it`ll mount on ?

Permanent installations require a bit of thought and are outside the scope of this article but there`s a picture below left of a neat method of attaching the pole to a canal boat.


Incidentally, you`re probably better not choosing white cable. It may look nice when brand new, but it`ll start showing up the dirt and then you`ll wish you`d gone for black cable !

Neat attachment for TV aerial, pity it`s a crappy contract type !

The above permanent install is nice and neat, though I can`t say I`m impressed by his (or her) choice of crappy Contract aerial though, especially a gold one !

Aerial attached to gang plank, non destructive and neat

Now this is a good idea, you can mount the aerial in the highest spot available without drilling into your pride and joy !  I`d have thought a slightly stronger mount would be better though, e.g one of our straight loft kits.

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Removable aerial mounting Removable aerial mounting, close up

If you haven`t got a gang plank to mount your aerial on try something like this. It`s one of our straight loft kits mounted on a 20" x 35" piece of 18mm plywood. I tried it when we were on the River Great Ouse and it worked fine. It was stable enough to not blow over despite the wind requiring us to swing round on the bow then reverse off the moorings, more than once....

Make sure the feet on the corners are “grippy” type rubber, plastic ones would be more likely to just slide in any wind.

Use roofing bolts to attach the loft kit to the board, because their low profile heads won`t stand too proud below and then touch the boat`s roof.

It will be noted that a 3ft x 1in pole will also fit the surface bracket. Thus, when it`s not too windy, you have the option of gaining an extra 16 inches in height by using the taller pole.  


Storage tip, removing the pole from the mounting (c/w aerial) takes up far less space on the boat (and ensures the aerial doesn`t get knocked off when going through a guillotine lock......).

Caravan / boat clamp

Caravan / Boat aerial pole clamp


This is quite a neat way to attach an aerial pole to a caravan or boat. The clamps can even be stuck on using adhesive pads which is good for those who don`t want to drill into their pride and joy, though it must be admitted that bolting, screwing or riveting the bracket(s) on would be rather stronger.The use of one, two or three clamps obviously increases the strength of the installation.

The capacity of the clamp is 25mm / 1” and they are a good complement to the 4 piece caravan pole.

Some people find wrapping tape round the pole, where it is actually clamped, helps hold it more firmly when there is a strong wind about trying to realign your aerial.

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Neat and strong use of a U bolt
aerialsandtv.com
Ehhhhh, not sure about this one........
aerialsandtv.com

A couple of contrasting contraptions.


The one on the left is neat and strong and it`s a reminder that simple U bolts or V bolts can sometimes suffice.


Not so sure about the one on the right. It may not involve drilling into the boat but

it looks a bit of a mess and has one other drawback which is not immediately evident.

Any idea ?    

The wooden clothes peg will eventually rot.

Bet you didn`t think of that did you ?   

Lateral thinking.

That`s what won us the war.......*

Incidentally that “pole” looks suspiciously like part of an aerial cradle to me.

Through bracket Through bracket, side view

The Through Bracket on the right is a neat and quite strong, for a short pole anyway.


These clamps only take a 1” pole.

(Low profile wall brackets will take up to 2” poles)

A refinement on the use of a loft kit is to replace the nuts with wing nuts, this makes it much more convenient to dismantle your aerial from its mounting without having to drag out a spanner. But we all know cheap wing nuts are prone to stripping so use decent ones !  These die cast M6 wing nuts also enable the use of a spanner to increase the torque if so desired.

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Die cast wing nuts in use on a loft kit mounting.
Wing
nuts in
use on an
aerial mounting


Four section aerial pole (as also supplied in our caravan aerial kits).


The pole has three sections at 3ft and a “shortie” top section (at 1ft) to which the aerial can be left attached, thus avoiding the chore of clamping it on each time you want to use it. It should be noted that if wind conditions dictate you do have the option of only using 2 or 3 of the sections giving you a shorter stronger install. The 4 detachable clips can be used keep your cable tidy (though for permanent installs we actually recommend insulation tape).

Double Clamp  (as also supplied in our caravan aerial kits).


Neat removable way of attaching an aerial pole to another vertical tube. These are particularly well suited to bolt an aerial pole onto a caravan jockey wheel, as shown right. It is possible to use just one “double clamp” and push the bottom end of the pole into the earth, but if parked on hard standing then you need two, as is shown in the picture. Whilst it is preferable to support any aerial pole further up, bolting a 9ft caravan pole to the jockey wheel was actually a bit sturdier than I expected.

#DoubleClamp Double clamp assembly

* well that plus the Royal Navy and the English Channel......

The Satellite Option


You can use a satellite rather than an aerial to receive your signals, though you`ll usually require a separate satellite set top box in order to do so, but what are the relative merits of satellite v aerial ?


Basically it`s swings and roundabouts. There are places where a satellite will work perfectly and an aerial will only give a poor signal, but on the other hand, there are places (e.g. with trees or buildings in the way) where an aerial will work and a satellite won`t work at all.

Setting up an aerial is usually much easier than a satellite, particularly if there are any houses around, you just point your aerial in the same direction and polarity as theirs, retune your TV, and that`s it, no meter, no fine tuning the dish, nothing. When analogue was switched off the digital signal was greatly increased in power so less problems should be experienced finding a signal, but on the other hand the “old” analogue signal was more reliable in poor signal areas, albeit at poorer picture quality, than the digital one. Unfortunately analogue`s gone..... I accept that there are times when it`s not that simple to get a decent signal from your TV aerial (for those see the article above) but we regularly get people buying aerials because they find setting up a dish too much hassle. I personally find them too much trouble so we don`t even sell satellite stuff for boats/caravans, but that`s not saying some people won`t find it a viable alternative though you should bear in mind that satellite tuners do tend to increase the current draw from your battery, particularly if it`s a set top box in addition to the TV. One other thing, it`s not unknown for people using satellite dishes on their caravan or motor home to have problems when they go up to Scotland, particularly north Scotland. This is to do with the curvature of the earth and the fact that as you go further north you need a bigger dish to receive the same size signal. This is why the standard Sky dish in England is 43cm, but in Scotland its 60cm. On the subject of dish size, when it comes to satellites, the size of the dish has an important bearing on ease of setting up and the reliability of the received signal. Basically a smaller dish will have a wider acceptance angle than a larger dish. This is good and bad. It`s good because it`s easier to aim it at the satellite and therefore quicker to set up. This may explain how come aerial installers use £300 meters to set up a domestic installation (and take time doing so) when some caravanners/boaters can, apparently, do it in 5 to 10 minutes with a £30 meter ! Furthermore the wider acceptance angle also means that there`s less chance of the signal going off due to movement (e.g. of a boat at its moorings), though this would not normally be a problem in a caravan, unless you`re in an earthquake zone, or your suspension is soft and there are hurricanes about, or someone you wouldn`t want sitting next to you on a plane* is vigorously moving around round inside your van. The down side of a small dish is the quality of the signal can never be as high as with a large dish, for the same reason that an Omni directional TV aerial cannot ever give as much signal (or gain) as a directional one. Less signal from your dish means that there`s a greater chance that bad weather will affect your reception, so, at the end of the day, you pays your money,

and you takes your choice.


* staturewise

How high to mount  your aerial ?       Well that`s a big question.......

Generally speaking the higher the better, at least that`s the usually case with aerials.

But not always.

In the past we`d done tests on aerial heights for installations mounted on roofs, but what about at the kind of height the average boat or caravan owner would have his antenna ?

Whilst checking up on the accuracy of testing aerials at 6ft (it is accurate by the way.....) I also compared the signal at the test site at 6ft and 12ft, which is about the sort of heights that boaters and caravanners use.

I measured the received signal off three transmitters : Emley Moor, Bilsdale & Belmont.  The transmitters were in three different directions, and there was "line of sight" to all of them.

The results are fascinating.

An increase of 4.1dB (which is signal rise off Emley Moor) for raising the aerial only 6ft is huge. To put it into context that`s not far off the increase in signal you`d get by swapping a little 3ft 6in DM Log for a big 5ft 3in DY14WB !  Even the 2.3dB increase off Bilsdale is a significant improvement.

However.....

Off Belmont there was actually a huge 4.8dB decrease ! Why this should be when there was nothing between the aerial and the transmitter (albeit 65 miles away), well your guess is as good as mine. It`s a perfect example of RF being a black art.


Note the spread of results, the averages can give a misleading impression (as is the case so often). Some signals off Belmont wouldn`t be that much different, but one in particular was 8dB down. Now that is massive amount, but, of course, even with that reduction the TV may still work perfectly if the signal strength was high enough, which at this location it would be.

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Results of testing an aerial at boat / caravan height. How high should I mount my caravan / boat aerial ?

How high to mount your aerial.

Four piece (9ft 4in) caravan pole with detachable reusable cable clips.

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If you`ve found this site informative and, hopefully, interesting as well,

please help us increase the number of people reading it.


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Post Switchover Post Script


The first trip we took after the (complete) switchover over reminded me very clearly how finding the best digital signal is so much harder then finding the best analogue signal was. The main problem is that the digital signal is either there or it isn`t, though there is a narrow band of signal quality when the picture`s there but it`s breaking up and freezing all the time.

The first night we were moored at Claverton (visit the pumping station, very interesting) on the Kennet & Avon canal. We were right in a valley and there wasn`t a house nearby so I could check which transmitter it was getting its signal from !  I pressed on, but despite me having the advantage of knowing the direction and polarity all the transmitters even when using the DM Log the TV`s tuner couldn`t find any signal off Mendip, Ridge Hill, Oxford, Hannington, Rowridge, or even the Bath relay. Salisbury did give a bit of a signal but it wasn`t usable. This complete absence of signal has never happened anywhere before (in fact I even suspected the TV was faulty) though I only mount  my aerial only about 18" above the boat`s roofline because I don`t have the option to mount a higher pole on a hire boat.. Not that I`m saying a higher aerial pole would necessarily have made a significant difference. Obviously, at this site, the boat`s Omni type aerial didn`t find anything at all, even off Salisbury. As an aside were we were moored there were trees all round us so even a satellite would not have worked. Anyway, we stopped at Bathampton the following day which is right next to Bath transmitter and the TV operated satisfactorily there, in fact even the Omni aerial worked in that location !  

Of more interest was when we moored at Hilperton. There, even though it was through trees, the DM Log managed to get a reliable signal from off the first transmitter I tried which was Mendip. However when I tried the Omni as an experiment the signal was breaking up all the time.


I`m unconvinced if the TV`s tuner was sufficiently sensitive (they do vary), but even so, TV reception wise, it was a sobering trip. I suspect that with analogue we`d have always got something, even if at Claverton it may well have been grainy and ghosting, but, unfortunately, analogue`s gone........

So, a reminder of the overwhelming importance of signal strength. In some spots you won`t get anything whatever aerial you use, whereas in some spots even an Omni will work. What`s most interesting to me are the areas, like Hilperton, where a decent aerial will get you something, but a crap aerial won`t.


In 2013 we went for a week on the Monmouth & Brecon canal, and what a fabulously scenic canal that is, particularly when the weather`s good, which it was !  We were told “you can`t get a signal at most spots, watch DVDs instead”. Well I don`t actually watch that much TV, but I do have an interest in whether it`s possible to get a TV signal ( ! ) and I have to tell you that at all 5 locations I tried it I got a signal using our DM Log. I`m sure there are many locations on the M&B where even a DM Log wouldn`t work, but it did wherever I tried it. You do have to know where the transmitters are though, and the fact they`re all vertically polarised, and don`t use an Omni !


I thought the Norfolk Broads would be all flat, that was how I remembered them from holidays as a kid, but when we went for a short break on them in 2014 I realised it`s not (quite) like that ! Our DM Log worked everywhere we moored to a greater or lesser extent, though it must be admitted the signal at Rockland St Mary wasn`t perfect. At the staithe there the aerial is aligned WSW onto Tacolneston and firing through a load of trees and a hill ! It was just about OK with the odd glitch. The boatyard supplied XB5 (with no reflector….) didn`t work there at all.

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Worked Example of Using an Omni to Maximise Picture Quality


As mentioned above, we spent a night at the foot of Bosley Locks, 4m NE of Congleton. 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 DM Log. 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 CH 52 and BBC2 on CH 45 (analogue days….). 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. So I cranked the DM 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 kicked out 500kW (analogue), Moel Y Parc was 48 miles and only transmitted at 100kW.

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

NOTE ! Most of the tests on this page are on analogue transmissions but analogue signals showed up small differences in signal strength/quality better than digital signals so the tests are actually more meaningful than those on digital transmissions.


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

There are some other smaller repeater transmitters in the same area (Over Biddulph, Congleton, Langley and Macclesfield) which can be seen on the full size version of the aforementioned map, or see Ofcom`s PDFs or Digital UK (use the drop down menu to change the region).

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 (on a boat or caravan) 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). If you get the wrong polarity you could be losing up to 90% (or more) of your signal, which isn`t to say it won`t still work if the signal strength is high enough, but if it isn`t, well, no Coronation St for you.


(Link to The Three Variables)

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Also 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, by using an omnidirectional or "Omni” aerial. The problem with this strategy is that, how can I put this, Omni`s are crap...... In fact the gain of an Omni is actually negative, theoretically it`s minus 3 dB, and that`s without taking into account the additional loss of signal that results from an incorrectly polarised antenna.  Furthermore an Omni`s beam width (to eliminate unwanted signals), is, well, 360° !

The DM Log is pretty strongly made and because it`s nearly all metal in construction it`s eminently fixable if it gets damaged, as any touring aerial is bound to be...... Furthermore, Log aerials are flat, thus making storage much easier and lowering the risk of the antenna being damaged. At a conservative estimate the gain of the DM Log 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. Now it must be admitted that 7 dBd is not "high gain", but since all high gain aerials are large, and as such are unsuitable for boats or caravans anyway, I wouldn`t worry about that too much, particularly, as we`ve just discussed, when an Omni has minus 3dB of gain. So, compared with an Omni, a DM is high gain !

On the subject of which, we sometimes get asked if a Log36 would be a better choice (for a boat/caravan aerial) than a DM Log because its gain is a bit higher. Well yes and no would be my answer. You do get a bit more signal out of a Log36, but on the other hand the DM Log is 10in shorter, it has a tilting clamp, and, most importantly, it`s more easily fixable if it gets damaged. Whilst testing an aerial I once bent some of the alloy rod type elements on it, but when I tried to straighten them some just broke off !  Furthermore, if any spares are needed for this aerial (or any other purchased from us) we`ll try and get spare parts for it if possible. Lastly, the DM Log also has a handy 6" trailing lead c/w rain proof cover, so, basically, I`d always recommend the DM Log, and only the DM Log.      See customer feedback using a DM Log.


Note : we recommend that all Log Periodic aerials are installed slightly tilted up at the front end.

DM Log aerial


It`s the only antenna we recommend for boats and caravans.

There are many great mysteries in this world of ours, like the Mary Celeste, and why some lazy ignorant drivers put all that effort into winding down their window and throwing their fag end out of it, when it`d actually require less effort to put it in the ashtray........

But along with these imponderables must rank why boaters or caravanners use Bacofoil X Beam type aerials like the ones in the above pictures. You see loads in use, in fact a large percentage

of the boats I see around seem to have them, but X Beam type aerials are fundamentally

unsuited to use as touring aerials. The reflectors mean they take up a lot of room, unlike a flat

Log Periodic aerial, and the “Xs” are hardly space saving either. Furthermore the X type directors are often a weak point on even the best of the X beams. But these Bacofoils (usually marketed as SLX, Philex or Labgear) must be the flimsiest aerials ever sold, in fact I`d say they`re only really suitable for use in lofts where there`s no wind, no birds and, hopefully, only small spiders....... When one remembers that touring aerials are usually put up and down every few days, and bashed about generally, the use of Bacofoils becomes even harder to understand.

Maybe the Bacofoil(s) are also used for the Sunday roast ?  (think about it, I didn`t get it at first)

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Maximising Your TV Picture Quality on a Boat / Caravan

Before we go any further, don`t forget the obvious, which way are the other aerials facing/polarised ? And this is likely to be more accurate for any houses (as opposed to other boats or caravans) as they were probably put up by an installer with local knowledge.

Extract from our transmitter map.

Omni directional ("Omni") TV aerials, only recommended if you can see the transmitter !

If you get a good picture off an Omni TV aerial it`s because you`re in a good signal area, in fact I reckon that a coat hanger* would work just as well, actually, it may well work better. The fact is that in a poor signal area an Omni aerial is about as much use as a 2nd World War Italian Kamikaze squadron**.

Tests of commonly used touring aerials


In July 2013 I spent quite a few hours up at the test site putting the most commonly used caravan aerials through their paces. All these aerials are Log Periodics, there are no Yagi type antennas here because in my opinion they`re not really suited to caravans or boats. Thus I went for a Status 550, an Image 18 (420), a 20 element (15” long”) Mini Log, and finally the aerial we recommend for touring, a DM Log plus its shorter 18 element brother, the DM18 Log. The approximate gain curves are below. It should be noted that even the DM Log is not a “high gain” aerial (see these high gain aerial curves compared to a DM Log)  but high gain aerials aren`t suitable for caravans or boats. Having said that, even the lowest gain of the aerials on test here is “high gain” compared to an Omni aerial !


Last, but by no means least, an amplified low gain aerial is not, by any means,

the equal of an unamplified aerial with higher gain.

Tests of caravan / boat aerials : Staus 550, Image 420, Mini Log, DM18 Log & DM Log

Notes

In reverse order of performance we have :


Status 550

This is undoubtedly a clever design, particularly the fact you can leave the aerial up all the time, and adjust both the direction and the polarity of the aerial from inside your caravan, though you do have to drill a hole in your roof, and it looks crap on a narrow boat. It has the lowest gain of any of the aerials on test but, let`s be reminded, it`s still far better than an Omni. Inside that casing (see below) is a little 18 element log periodic aerial. The aerial in the picture is vertically polarised, aiming at Oughtibridge relay in fact.

What`s inside a Staus carvan aerial ! Status 550 caravan aerial

Ever wondered what`s inside a Status caravan aerial ? Now you know !    (Link)

The aerial`s made of tin foil but we can excuse that as its permanently sealed into its casing.

Note the VHF elements tagged on the back, These may be the cause of the 2dB drop in gain over the Image 18 aerial I also tested though the drop off is more likely due to the fact that cable routing on a log periodic is very important to maintain the gain of the aerial and on this design (unlike any other log periodics) the cable travels back on itself before routing off down the pole.

What`s this ! The manufacturers of the Status  use (certainly up to May 2013)  Low Loss CoAx !  That, is an inexcusable bodge, I can`t imagine what they were thinking….  And, unlike every other aerial manufacturer, they wouldn`t lend me an aerial to test, I actually had to buy one (what did they have to hide, the cable perhaps….), so thanks for that, not. (Link)

Staus 550 aerial is wired up with Low Loss CoAx ! ! !

Image 420


These may not have quite as much gain as a DM Log (nor are they as fixable when damaged) but for their size they actually work pretty well. Note the adapted clamp, the aerial I had didn`t have a clamp and its unorthodox construction meant a conventional clamp (and pole) won`t fit it. Finally, and somewhat surprisingly, the cable is Low Loss Coax !  If I were buying one of these I`d buy the 420 rather than the 430 with the VHF elements as they may well negatively affect the UHF gain.

NB : They look crap on narrowboats !

Image 420 TV aerial

DM18 Log and DM Log


The DM Log is the shorter (2’ 6”) and slightly lower gain version of the DM Log (3’ 6”).


Come with tilting clamps, have all metal construction, robust and, even more importantly, easily fixable when they do get bent.


More details of the DM Logs here.

DM 18 Log TV aerial DM Log TV aerial Mini Log Periodic

Mini Log


For their size these give a fair signal. The one I had wouldn`t mount vertically polarised (I had to fart about with an L section pole….), also the rod type alloy elements can snap off if you try to straighten them when they get bent. Bill Wright reckons the polar plots of these are very poor though that may equally apply to all small Logs.

Full results

What you really need to know about caravan and boat aerials....... Aerial polarity, it can be important !

Note : analogue is not transmitted anymore, but for the purposes of aerial testing it is actually a superior indication of degrading signal quality than digital therefore these tests are still relevant.