If you`ve found this site informative and, hopefully, interesting as well,
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, though I did have rather less luck with the Omni fitted on the boat. They`re half right, “you can`t get a signal at most spots with the Omni aerial, watch DVDs instead”….. I`m sure there are 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, most importantly, 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.
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 unlikely 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......
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.
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.
Also see maximising picture quality
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 3dB, and that`s without taking into account the additional loss of signal that results from an incorrectly polarised antenna (see above). 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 7dBd 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 7dBd 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 when, as we`ve just discussed, 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. Once, whilst testing a Log36 aerial, I accidentally 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. Also see : maintain your DM Log, customer feedback using a DM Log, use of a cradle with a Log Periodic aerial, and, finally, 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.
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.
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 (a metal one, obviously….) would work just as well, actually, it may well work better. The fact is that in a poor signal area an Omni TV aerial is about as much use as a 2nd World War Italian Kamikaze squadron*.
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 due to their size / windloading and susceptibility to damage. 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.
In reverse order of performance we have :
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.
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 reduction 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 the cable routing is back up the aerial boom (unlike all other Log Periodic aerials, including the Image).
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)
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 which is particularly unfortunate because we recommend that Log Periodic aerials are tilted up slightly at the front. 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.
DM18 Log and DM Log
The DM18 Log is the shorter (2’ 6”) and slightly lower gain version of the standard 26 element DM Log (which is 3’ 6” long).
They come with tilting clamps, have all metal construction, are robust and, even more importantly, are easily fixable when they do get bent.
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….), and it isn`t easily tiltable. Also, important for a touring aerial, the rod type alloy elements can snap off if you try to straighten them when they get bent, which they will. Bill Wright reckons the polar plots of these are very poor though that may equally apply to all small Logs.
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.
Note : white aerials look crap on narrowboats !
If all else fails you could try one of those basic signal strength meters. I have to say I briefly tried one of these (given to me as a freebie), and I found it inconsistent to use as a transmitter finder, I actually found it less trouble to just research where the TXs are ! Anyway most professional installers would laugh at those cheap signal meters 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.
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……
Installing a pole on a horizontal railing
If installing a vertical pole on a horizontal rail our 2x1 clamps could be considered. Even better our M8 (stainless) wing nuts fit them in order to facilitate easy removal. Unfortunately the 2x1 clamps are only available in pre galv pressings with a zinc plated V bolt, however the 2x2 clamps are available in hot dip galv or stainless.
Also available is the 10ft (actually 9’ 9”) heavy duty 1.5” x 2 piece caravan pole. Made up of 2 x 5ft sections this is much stronger than the 1” x 4 section model. I wouldn`t have thought it`d be that much weaker than a 10ft one piece pole.
A Yagi aerial with no reflector is losing almost half its gain. A Log Periodic aerial would perform just as well, in fact if the Yagi aerial was a small one (e.g. an XB5) the Log would definitely perform better……