Omni Directional Aerial

[annv]

One thing i will mentian   the fuse blew  of cause it has to be a very small one that i didn't have its only a .25 amp fuze only Wards keep them i fitted a one amp fuze and now have a spare hasn't blown since 4 years now suggest you carry a spare fuze it will then never blow. John

[JennyMorgan]

Perhaps a FreeSat set up is worth considering. I have several 'showman' friends who are on the road all summer, their wagons all having been set up for satellite. Doesn't matter where they are, they get a good signal. My own house is in the shadow of a big house and with FreeSat I have absolutely no problem. You can also have auto-tracking, useful for the crew when under way! Hight ceases to be a requirement. 

[BroadAmbition]

JM, Tks for your suggestion.

We have got one.  Yes it worked fine but yet again it's a proper load of faffing around setting it up.  A long cable to shore, the dish must be put on the ground, no good onboard as the tiniest movement loses the satellite.  You then have the concern of someone tripping over the cable in the dark, plus it won't work on many wild moorings due to the vegetation being too high etc.  We don't want to view underway and couldn't even if we wanted to due to the location of the TV when set up so a tracking system would be wasted on us.  Then there is the storage issue of the dish & gear when inboard once again.

We've been there - Not for us

Griff

[BroadAmbition]

And the fourth one to enter the fray.  This one recommended by our professional aerial / tv installer (Ret'd)  30dbi is impressive as is the price as is the 100% 5 star ratings from satisfied customers it has received.

https://www.ebay.co.uk/itm/OMNI-DIRECTIONAL-CARAVAN-MOTOR-HOME-BOAT-TV-DIGITAL-FREEVIEW-BOOSTER-AERIAL-KIT-/192090207476

Griff

[Hockham Admiral]

30 dB is certainly impressive, Charlie! The table shows dB to signal gain values... x 1000!

dB value	times by
+30 dB	1000
+20 dB	100
16 dB	40
13 dB	20
10 dB	10
9 dB	8
8 dB	6.31
7 dB	5.01
6 dB	4
5 dB	3.16
4 dB	2.51
3 dB	2
2 dB	1.58
1 dB	1.26
0 dB	1

[MauriceMynah]

Is "Omni directional" the best way forwards? I genuinely don't know. I tend to think that a directional aerial might be better as it wouldn't be picking up so many spurious signals (and amplifying them).

Perhaps some of our radio experts can enlighten us.

[grendel]

1 hour ago, MauriceMynah said:

Is "Omni directional" the best way forwards? I genuinely don't know. I tend to think that a directional aerial might be better as it wouldn't be picking up so many spurious signals (and amplifying them).

Perhaps some of our radio experts can enlighten us.

Actually MM, I think you will find that omni-directional is any way forwards 

[woodwose]

I can't recommend any particular aerial as I would not dream of watching TV on the boat and so don't have one. However, I am a radio ham with lots of experience of messing about with aerials so I can give out some information which I hope is helpful:

The TV signals on the Broads come from the transmitter at Tacolneston. This is to the south of The Broads and quite a long way from some places. The transmitter power there was increased when the old analogue signals were switched off and this improved reception generally, but boats are low down and often get behind trees and other obstructions which can give problems. The signal from Tacolneston is horizontally polarised so your aerial must be correctly oriented. Cross polarization greatly reduces the signal.

The rule of thumb with aerials is the higher and bigger they are, the better they will work.

The co-axial cable connecting the aerial to the receiver is just as important as the aerial. It should be good quality, dry, undamaged and have no joints. Connectors must be correctly fitted and preferably soldered. If water gets in then the cable is junk and you need a new one. If reception is poor or suddenly gets worse, look at the co-ax first. The connectors must be clean and free from corrosion. The outer sheath or braid is not a screen. At these frequencies, the co-ax acts as a transmission line with the signals travelling on the surface of both the inner and outer conductors. Any damage or joint can look like a short circuit to the signal.

Amplifiers or boosters are no substitute for a decent aerial. They amplify noise and unwanted signals and can cause a range of problems.

Passive splitters or diplexers greatly reduce the signal strength. They will at best halve it.

If an aerial is advertised as being a miracle aerial then this means it will be a miracle if it works.

Aerials that look like dart boards are best for playing darts.

Omnidirectional aerials are often small and have no gain so they work best if mounted as high as possible. They have the huge advantage that you don't have to point them at the transmitter so they work on swinging moorings or when you are motoring along twisty rivers.

Directional aerials have gain and this means that they effectively boost the transmitter power. As seen in the chart a few posts ago, a gain of 3db is the equivalent of doubling the transmitter power. This is just about enough to notice a difference. However, they work best in static situations. They are not so good when you are on the move. Many aerials have gains much more than 3db and they also reject unwanted signals and noise.

There are two types of directional aerials in the shops. Yagis and Log Periodics. They look similar but are not the same and work in totally different ways. Yagis have more gain and are simpler aerials. However, their bandwidth is fairly tight so it is important to buy one made for the Tacolneston transmitter. They will give the best reception and will be cheaper. Log Periodics have less gain than Yagis for similar size aerials but they have a wider bandwidth and are suitable for travelling round the country in a caravan or similar. They usually cost a bit more and are not really necessary on the Broads.

So, in summary: Mount it high, use good quality cable. Look at the aerials mounted on the houses in the area, get one the same and point it the same way. Yagis are cheap and high gain. Omnidirectional is best for moving boats but has no gain.

Nigel, Ham radio station G4AXA, Ludham

[MauriceMynah]

Thank you Nigel, that's just the sort of info I was hoping for. Just one question, I need a new aerial. How can I tell by looking if I'm looking at a Yagis or if one I'm looking at is a Log Periodic? 

[MauriceMynah]

Oh sorry, … and where would you recommend I buy high quality Coax? (and what do I ask for?)

[woodwose]

Yagis and Log Periodics look similar. However, Yagis are more oblong looking with most of the elements about the same length. Log Periodics tend to taper more with the elements getting shorter and shorter.

Having said this, there are lots of different designs so it can be a bit difficult to tell. If you are buying a new one, the seller should know.

I think RG6 co-ax is commonly used for short runs with freeview and should be fine for boat applications. There are waterproof and low loss cables available if you want to spend more. Lots of places sell it - Screwfix, Amazon  Toolstation and many more. Any aerial shop should also have cable.

Hope this helps

Nigel

[NorfolkNog]

Thanks Nigel, that's very helpful.

I did a bit of Googling and came across this site which is an interesting read and full of information. The guy certainly doesn't pull his punches in some of the comments but certainly knows his aerials!

Nigel's comments are far more succinct but if you have plenty of time to spare it's worth a read. Basically says exactly what Nigel said but a bit more long winded!

http://www.aerialsandtv.com/touringaerials.html

 

[SPEEDTRIPLE]

Hi Nigel, good to see you on here again.

Ditto the comments above from me too. I`ve been trying to get the ariel system on Lightning changed, or considered to be changed by the other owners, and this information will help dramatically to find the best equipment. Thanks for taking the time to write it.

[scraggs]

I bought one of these last year to use on the boat 1byone ariel very impressed with it considering we leave it in the cabin while watching tv, I just bought another to use at home on the spare room tv to save messing about with a proper ariel.

[annv]

Surly a boat tv aerial needs to be robust and small enough to be left outside semi permanently without being blown of direction,easily dropped for bridges,  having to dismantle and pack away each time you use it  leads to broken parts, damage to paintwork, and on the broads you only need one band for Tacolneston transmitter. John

[BroadAmbition]

Hi Woodwose,  I'm missing something here, you kindly informed us as per below:-

Omnidirectional aerials are often small and have no gain so they work best if mounted as high as possible.

Yet the Ballade aerial I'm considering states 23:5db  so what am I missing here or am I reading something wrong?

Appreciate your expertise and advice in this topic btw,

Griff

[woodwose]

Hi Griff.

The aerial itself has no gain, but the one you are looking at contains an amplifier which claims to have 23.5db of gain.

Nigel

[BroadAmbition]

Right Gottit,

That's that answered that un in straight-forward Yorkshire speak - Which I can understand.

So, t next question is,  Do differing omni aerials work better with that there Tacolneston Tx'er or are they pretty much all the same?

Tks

Griff

[MauriceMynah]

As I understand it, the bigger it is, the better it is, and the further up you can get it, the better too.

Note to self,... Stop right there.

[woodwose]

Hi Griff. I can't speak for any particular aerial because I have not used any of them.

Here are a few more thoughts

By definition, omnidirectional aerials cannot have any gain. A true omnidirectional device actually has a gain of -3db.

Some of the aerials on the market claim to work from 40 to 900MHz. The chances of such an aerial being resonant anywhere near the frequencies used by the Tacolneston transmitter are not great, so that is a further loss.

Such aerials are accompanied by a broadband amplifier which also amplifies the noise as well as the signal.

Inside the plastic globe or flying saucer will be a sort of folded dipole which resembles a bent coat hanger (there may be more than one). This is the actual aerial. The higher this is the better it will work.

I am not saying that omnidirectional aerials don't work and they have the big advantage of working on swinging moorings.

If I was buying an aerial, I would get a Yagi made for Tacolneston (Group BH). I would mount it on a pole as high as possible and would not use an amplifier. An 18 element one would be better than a 10 element but it depends on how much room there is in the boat to store it.

Hope this helps

Nigel, sunny Ludham

[BroadAmbition]

Thanks for your expert advice - Very good of you

Griff

[NorfolkNog]

Got to agree, the higher the aerial can be positioned, the better. Mrs N and I very rarely watch TV, usually the aerial is stowed away and there it stays. However a few years ago we hired this one with a very simple but effective telescopic pole. It simply fitted into a socket on the deck and extended well above the height of the boat. The aerial looks to be the Yagi type which Nigel recommended. I do recall reception was superb, probably the best we have achieved the few times we've used a TV. I don't suppose this arrangement would present any problems as a DIY job. Should be fairly cheap too!

[MauriceMynah]

That is the size and design of aerial I use, I think (from what I have learned on this thread) that I need to replace the coax though.

[ranworthbreeze]

That is the type of pole is similar to the one we have on Ranworth Breeze it can be clipped to the boat rails, we use the following aerial however which can be purchased as well as the pole from Brian Ward's

http://www.brianwards.co.uk/audio-tv/televisions-aerials/image-420-directional-antenna.html

Regards

Alan