DAB and FM combi aerial

[Simon T]

Has anyone had any experience of using these combined FM and DAB aerials by Antiference?

Any good?

[tony sayer]

In article , Simon T scribeth thus

Wouldn't give it house room, get a Vertical FM dipole and that will suffice much better...

[Brian Gaff]

What design is it? I know one exists that has two fm elements and about four vertical dab elements diplexer together at the connection box and presumably undiplexed at the bottom. However, whether you actually gain anything unless you have a difficult reception area, is a moot point. the other things I've seen are basically just a vertical rod and aan fm dipole or halo. they are probably not worth bothering with, as any old bit of alluminium free from obstacles would probably perform OK in a normal signal area.

Brian

[Mark Carver]

That's what I use. DAB performance is no worse (or better) than a dipole cut for Band III, I discovered after conducting an experiment,

[alan_m]

or

[Graham.]

The short answer is it will probebly be fine unless you are in a challenging reception area.

The long answer is that this type of aerial is disliked by those of us who know a thing or two about aerials.

The DAB part is OK, the problem is the FM "halo". It attempts to provide omni-directional reception using the horizontally polarised signals from the transmitter. These are retained largely for legacy reasons, and a more effective omnidirectional aerial would use the vertically polerised component, as all HP transmitters also have VP (mixed poleroisation). This would be a second (longer) vertical dipole.

Worse still, a few FM transmitters do not carry the horizontal component at all, in which case your halo will be as effective as a piece of wet string.

That's not to say that wet string cannot deliver perfect reception in a good signal area when mounted high up.

[Simon T]

Thanks, I've read that article. But the aerial I was interested in wasn't in the review.

Ahh yes, thanks for that link, seen that gallery before, but had lost the URL. Always good for a chuckle!

[Andrew Gabriel]

A band II aerial (FM) and a band III aerial (DAB). They are both folded dipoles. The band II is omnidirectional horiziontally polarised (i.e. wrapped into a most of a circle, and the band III is vertically polarised in the centre of the band II circle.

There's presumably a diplexer to combine and impedance match inside the connection block, but that's not visible.

[Andrew]

Or buy a house that still has a Band 405 TV aeriel attached to the chimney. Could be a bit tatty by now.

However, there is only such much that DAB can be improved (sows ear, silk purse).

[Bill Wright]

At the risk of reiterating the words of others. . .

These things are made to sell, not to use. Two separate aerials are better, and both should be vertical dipoles. I have discussed these combined aerials with two manufacturers and the reason the FM is a halo is because two vertical dipoles on the same boom would be an obviously pointless product and there might be interactions.

It's good to have a folded dipole for DAB because you might need the extra bandwidth this has over a non-folded one, if they start using the lower channels.

If the aerial shown has a combiner/diplexer in one of the junction boxes I should think it would often remain unused and two downleads would be fitted.

Bill

[Michael Chare]

I use a DAB folded dipole for both DAB and FM. I am not that far from the Wrotham transmitter.

[Bill Wright]

A vertical unfolded FM dipole without a balun will work remarkably well for DAB.

A folded FM dipole will have to have a balun, and it will be much less effective for DAB (I'm not contradicting the poster above).

A unfolded DAB dipole will work a bit on FM.

A folded DAB dipole will have to have a balun, and it will be useless on FM.

Bill

[Michael Chare]

Thank you for the information. I possibly have just what I need!

Recently I have had some FM 'interference' which is probably receiver overload and can be stopped by unplugging the aerial lead from the wall socket.

[tony sayer]

Can you say where or roughly where you live so we can see what the serving transmitter is for your area?..

[Michael Chare]

I'm about 7km sw of the Wrotham transmitter, and just about have line of sight if you ignore the trees.

[tony sayer]

Blimey!, thats the "lighting light bulbs" sort of range!.

What you need is an attenuator. The aerial just a vertical FM dipole will suffice fine there, it needs to be a "clean" signal and then you need to turn it down somewhat.

One of these should make a good job of it:)..

Around 10 dB or thereabouts is what you'd need.

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