TV Aerial - what type ... any experts out there

[Rick Hughes]

Not strictly DIY ... but I will be installing myself, so not too off topic.

When I last bought a TV aerial you had to look up your transmitter (Kilvey in my instance) and choose correct group, (A for Kilvey) and set up horizontal or vertical to suit polarisation.

I have looked around and most of the combined Analogue/Digital ones I can see are no longer sold in different 'groups' they all seem to just state channels (21 to 68) which previously would have been a group W For example on TLC web site there are 19 element and 48 element versions of Yagi aerials, which is what I used previously (but of correct group) .... now there is no group choice.

it that the 21-68 covers all .. and therefore no need to be specific about groups ?

On a couple of web pages there was advice to buy a Wideband Digital, and the DAT45 seemed to be the most recommended. TLC ...

is a bit of an esoteric best to look at ... are they worth the difference ?

The problem is as usual, you don't have luxury of knowing how it will perform until you try it ... and waste of money if you buy the wrong one.

Rick

[Peter Crosland]

Post your query in uk.tech.digital-tv and you will find some very helpful people. Bill Wright in particular is a mine of information.

[John Rumm]

Yup - the procedure is still the same...

In practice, there is no such thing as a "digital" aerial - other than in marketing speak. A wideband aerial (i.e. group W) will cover the full spectrum and hence is sold by some as a "cure all" solution to getting analogue and digital TV without needing to do any research as to the actual group you need.

Yes that is the idea.

Note that in many cases you will be able to receive both analogue and digital without needing an wideband aerial.

If you don't need a wideband, then you are still better off with a "grouped" aerial (smaller, higher gain, less chance of interference etc).

To an extent this is true unless you have access to the required test equipment to analyse the signal you are currently receiving, and also some experience of how various different aerials will perform given your location and requirements.

If you look at:-

suggests that Kilvey Hill is a relay with vertical polarisation. It look like it carries all of the digital muxes and all the analogue channels. The channel allocation is:

MUX C 21 MUX 2 22 ITV 23 MUX 1 25 BBC 2 26 MUX A 28 CH4 29 MUX D 31 MUX B 32 BBC1 33 CH5 35

Which looks ideally suited to a group A aerial. Which I presume is what you already have. Hence if you are not receiving the digital stations then it suggests that lack of signal strength is the issue rather than the wrong group aerial.

If you get your OS grid reference from streetmap.co.uk (and that of your transmitter) you can plug them into the calculator here:-

should indicate the type of aerial (i.e. gain) you will need for the digital channels (assuming that your analogue reception is fine at the moment!)

[logized]

Wideband aerials are now often installed to cope with some of the digital channels being outside of the normal aerial groups. In your case, it looks like a band A should still be ok though -

the highest digital channel is 32 for your transmitter and the analogue are -

as you say, group A covers it.

If you do get a wideband type, then you would need it to be bigger to offset the fact that they are less sensitive than a narrow group aerial. Also, to get digital, you may need a bigger aerial anyway - check on the freeview reception coverage -

DAT45 aerial may be a bit too big though if you are in a reasonable reception area - do any nearby houses have those installed?

Dave

[Dave Plowman (News)]

That's because the old grouping of aerials didn't take into account CH5, let alone the digital multiplexes.

[Andy Luckman (AJL Electronics)]

I'm surprised that there has been no mention yet of balun requirement and double screened cable. An aerial (especially DIY shed specials) is not just a piece of bent aluminium waving in the air. It is important to use either a CAI benchmarked aerial or at least one that has the correct characteristics.

[Adrian]

Wouldn't most aerials supplied in DIY sheds be already matched to 75ohm downlead cable?

[Andy Luckman (AJL Electronics)]

Most definately not. They are typically just a standard balanced dipole affair. It doesn't help that a once respected manufacturer, instead of modifying their design, tried to convince us that, contrary to all the laws of physics, baluns weren't required on *their* aerial because they were so good. Guess which brand I no longer stock? :-)

[John Rumm]

Maxview?

[Andy Wade]

I imagine he was referring to the name beginning with 'A'.

[tony sayer]

Well the last one of they I saw had a balun, well a PCB version anyway...

[Andy Wade]

Their TC range didn't, but they've modified it now - to get through 'benchmarking' - to use an x-dipole like on the XG, which has used a balun for yonks.

[tony sayer]

In article , Andy Wade writes

Yes, just trying to think when that was...

Time goes a lot faster as U get older:(

[Rick Hughes]

Thanks for a very helpful reply .... I'll follow up on the links you advise. It does all point to group A ... so perhaps I should ignore the wide band versions.

Rick

[Rick Hughes]

I notice on the transmitter predictors that John Rumm pointed me to, that the results don't specifically mention Ch 5 only BBC 1,2 ITV & Ch4

IF I follow the table they show that for my OS grid ref (SS712938) that a gp A aerial is what is needed ..... and the same result come in for digital predictor, does this gp A include ch5 ?

Rick

[Rick Hughes]

Andy care to mention a make to consider ?

I posted the url in my original post of aerials at TLC, are these worth getting .... I am in a good reception area ... but this is a new build, and I might as well buy the right piece of kit as the wrong one.

Rick

if you prefer to reply direct, please feel free to do so.

[John Rumm]

Group A is usualy channels 21-35, or some aerial makers go as far as channels 21-40.

CH5 is on ch 35 from Kilvey Hill, so that is just inside the range of a group A aerial.

[Andy Hall]

I have two of the Televes antennas, although didn't buy them from TLC.

They are well made and give very good results.

.andy

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[Andy Hall]

Probably not a problem though.

CH5 is at an ERP of 10kW, the same as the other channels 23/26/29/33 (not all transmitters carry CH5 at the same power level).

However, some transmitters deliberately do not have uniform radiation in all directions in order to avoid interference with other transmitters on the same or nearby channels. For CH5 this is a bigger problem because channels 35 and 37 are very frequently used as a result of the need to shoehorn in an extra channel from the four originaly planned.

From the grid refs. I make it that Rick is just over 2 miles as the crow flies from Kilvey Hill, so unless there is another hill in the way, signal strength should not be a problem. A more likely scenario is multipath reception from other objects, so a directional antenna could well be a good idea.

I had this issue with reception from Hannington, and swapped antennas to a Televes DAT45 - resolved the problem. That TX is a difficult one because it ranges from channels 35 to 66 does not radiate uniformly and CH5 is 6dB down relative to the other channels.

.andy

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[John Rumm]

At two miles it is supprising he needs an aerial at all! ;-)

If he can get the digital muxes then it becomes a bit of a moot point anyway since that ought to get a decent CH5 into the bargain.

DTV is not as badly affected by multipath echos, in fact in some cases it can actually improve reception.