D A B Aerial

Sandancers

Sandancers

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I'm thinking of fitting a DAB radio , does anyone have experience of fitting an aerial for DAB on a windscreen which has built in heating element. Transit mk7 to be exact.

Or even fitting the aerial in the over cab?
 
I just used a cheapy magnetic one from Halfords and put it on the roof :)
 
Geordies said:
does anyone have experience of fitting an aerial for DAB
Click to expand...

just recently bought a Sony DAB radio and Autoleads window film aerial.. from Halfords..

still haven't got the radio to work on DAB , I think it's because the Hymer has no metal in the window A pillar to ground the aerial.. think I'll need to run an earth wire up to the aerial to give it a ground plane

The aerial instructions make no mention of heated windscreen, but advise against mounting on polarised screens. .

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Last edited:
ScotJimland said:
still haven't got the radio to work on DAB ,
Click to expand...

update..
just been out and ran a temporary wire from the film aerial's ground plane to the van chassis, and it is working.. but not 100% ... maybe that's down to where we live on the fringe of DAB reception
 
I use a small magnetic mount aerial from halfords. I glued a large washer to the plastic trim in the quarterlight window frame of our A class... works a treat...
 
EssexBoy said:
I use a small magnetic mount aerial from halfords. I glued a large washer to the plastic trim in the quarterlight window frame of our A class... works a treat...
Click to expand...
can you show a picture ?
 
Sure @ScotJimland...
I'm on the train home from work right now, but will take a pic later...

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Just remembered I've got a spare magnetic aerial if anybody wants one :)

Just pay the postage :)
 
ScotJimland said:
can you show a picture ?
Click to expand...
Here you go Jim..

The window frame slopes, so I bent the twig at the base so it stayed vertical...

The camera angle makes the aerial look all out of kilter, when it actually isn't...
 

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EssexBoy said:
Here you go Jim..

The window frame slopes, so I bent the twig at the base so it stayed vertical...

The camera angle makes the aerial look all out of kilter, when it actually isn't...
Click to expand...


I'm surprised you can get DAB on that aerial, thought it was really fussy about reception ?
 
So far I have not been impressed with DAB in any vehicle. It cuts out at a critical point in the news or a song that you enjoy. Got a BMW mini and a 1 series BMW.

MoHo reception is none too brilliant either but I put that down to the aerial in the side mirror housing and the head unit deals with both the TV and the reversing camera view so not keen to change it!
 
If DAB radios work inside a house thro bricks and mortar, you'd assume fitting an aerial like used by Essexboy, behind the overcab fibreglass would work. I realise I'd have to manufacture an earth plane for it to bolt to. Any thoughts on that ??

I think I'll fit a stick on aerial to the part of the screen clear of the heating element, see how it goes, if it's not too clever try going behind the fibreglass on the overcab, tho that is a bigger job.
 
Geordies said:
I'm surprised you can get DAB on that aerial, thought it was really fussy about reception ?
Click to expand...

Looking at the picture I would say that antenna is a pretty good compromise ( but it is a 1/4 wave and really needs a metal ground plane for optimum performance )

DAB is transmitted on 174 to 239 megs.. very very big band width !

The only true DAB antenna you would not want to fit on a vehicle as it would either be huge or require an automatic ATU ( aerial tuning unit ) to work

AND....

Just to make matters more interesting, some DAM transmitters use horizontal polarisation and others vertical..
In english, that means a normal vehicle type aerial which is mounted vertically will give VERY poor results if the local transmitter is radiating on a horizontal plane

As a by the by, as convenient as stick on aerials are, they do display an amazing lack of performance :(

And that folks is pretty much the sum total of what I know about DAB !!!

If someone could let me know what type of connector is used for the supplied antennas I might be able to take an educated guess at certain ( boring ) things and come up with a half decent design for a home brew jobby (y)
 
Jaws, I saw the following link..............http://nears.forumotion.co.uk/t365-car-dab-antenna-test-which-one-should-you-go-for#1090.................... and after reading thro it, I am pretty certain that I will NOT be fitting a DAB with a windscreen stick on aerial. I will just buy and fit the radio and then look into how to somehow fit an aerial in the overcab, behind the fibreglass. The lad who wrote the article lives in same town as me, but without joining his forum am a bit stuck on how to contact him.

So basically if you can give an advise on the aerial fitting as described, I'd be very grateful.
 
image.jpg
ScotJimland said:
just recently bought a Sony DAB radio and Autoleads window film aerial.. from Halfords..

still haven't got the radio to work on DAB , I think it's because the Hymer has no metal in the window A pillar to ground the aerial.. think I'll need to run an earth wire up to the aerial to give it a ground plane

The aerial instructions make no mention of heated windscreen, but advise against mounting on polarised screens. .
Click to expand...

Jim I had the same problem, I bought a sheet of Conductive self adhesive copper sheeting from Amazon & cut a piece that runs from the metal windscreen frame over the window rubber & onto the glass & connected the eart there. I then used an indelible black marker pen to colour the copper sheet.



Photo (not very good, attached)
Mike

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Last edited:
Wellllllllllllllllllll.
I have tried to find out what the impedance is of a DAB car radio is but no luck so far.. So this is an approximate design and does not take in to account velocity.. And Skin effect will depend on materials used for the construction.
It is based on an expected impedance of 50 Ohms.

This is what you are looking to end up with:
Broken Link Removed

It is the simplest design I can think of .. Originally meant for circular polarisation but it will work well on vertical and horizontal transmitted signals..
In fact the whole thing would have to be a compromise as said previously as the band width involved is massive to say the least, so the dimensions I will suggest are for mod band..

It could be made using some brake pipe or similar..

basics
Take a bit of something or other that has an over all length 68 cm
make a bend at 17 cm as in the above picture
Get some thing that has a circumference of 34 cm and bend the pipe around that ( again, as in the above picture )
bend the last 17 upwards..
As I say, all of this is a compromise and the antenna is not going to be used to transmit through so none of this is particularly critical

Coax.
Ideally use a length of coax this is multiples of 1.5 metres / .95 .. ( so for instance if you want about a 3 mtr lead it should be 2.85 mtrs long )
Again, I am presuming the impedance to be 50 Ohms.. if ( IF ) that is the case then something like RG58 will be perfect and is very cheap from any shop dealing with electronic type stuff.. Maplins stock it or its equivalent

Mounting.
If you use the correct ( again approx. ) length of coax you will have effectively made something that is called a ballun ( a posh word for a transformer that works at RF frequencies ) and in theory you should only need to connect the centre core to the centre of the horizontal ring
You can literally through the thing on the roof or somewhere suitable and it should work ( though putting it in to a plastic box and gluing it to the roof with a bit of sikaflex would be fantastic )

A much better option would be to make two of them and place them back to back..Join the centre core to one and the shielding to the other..


Now THAT is proly as close as most folk will want to go to the full on 'correct' answer to the issue

However.....................................

After a bit of research I have discovered that more and more transmitters are swapping to circular polarisation and boosting their output power to compensate

With that in mind here is a REALLY simple design and solution
A straight forward vertical antenna, just like a standard car aerial
BUT.. Not quite standard

Replace the coax ( car aerials have a very strange type of coax that is used to 'kid' the radio in to thinking the aerial is MUCH bigger than it really is ! ) with some RG58 and fit the correct plug to it for your radio ( coax length is not critical )

Cut the antenna to a length of 36cm ( presuming a centre frequency of 200 meg )
What you have done is make the standard antenna in to a 1/4 wave end fed ground plane type
Job done


Bet some of you wish I had never said anything now LOL !!!!!!!
 
Jaws said:
Wellllllllllllllllllll.
I have tried to find out what the impedance is of a DAB car radio is but no luck so far.. So this is an approximate design and does not take in to account velocity.. And Skin effect will depend on materials used for the construction.
It is based on an expected impedance of 50 Ohms.

This is what you are looking to end up with:
Broken Link Removed

It is the simplest design I can think of .. Originally meant for circular polarisation but it will work well on vertical and horizontal transmitted signals..
In fact the whole thing would have to be a compromise as said previously as the band width involved is massive to say the least, so the dimensions I will suggest are for mod band..

It could be made using some brake pipe or similar..

basics
Take a bit of something or other that has an over all length 68 cm
make a bend at 17 cm as in the above picture
Get some thing that has a circumference of 34 cm and bend the pipe around that ( again, as in the above picture )
bend the last 17 upwards..
As I say, all of this is a compromise and the antenna is not going to be used to transmit through so none of this is particularly critical

Coax.
Ideally use a length of coax this is multiples of 1.5 metres / .95 .. ( so for instance if you want about a 3 mtr lead it should be 2.85 mtrs long )
Again, I am presuming the impedance to be 50 Ohms.. if ( IF ) that is the case then something like RG58 will be perfect and is very cheap from any shop dealing with electronic type stuff.. Maplins stock it or its equivalent

Mounting.
If you use the correct ( again approx. ) length of coax you will have effectively made something that is called a ballun ( a posh word for a transformer that works at RF frequencies ) and in theory you should only need to connect the centre core to the centre of the horizontal ring
You can literally through the thing on the roof or somewhere suitable and it should work ( though putting it in to a plastic box and gluing it to the roof with a bit of sikaflex would be fantastic )

A much better option would be to make two of them and place them back to back..Join the centre core to one and the shielding to the other..


Now THAT is proly as close as most folk will want to go to the full on 'correct' answer to the issue

However.....................................

After a bit of research I have discovered that more and more transmitters are swapping to circular polarisation and boosting their output power to compensate

With that in mind here is a REALLY simple design and solution
A straight forward vertical antenna, just like a standard car aerial
BUT.. Not quite standard

Replace the coax ( car aerials have a very strange type of coax that is used to 'kid' the radio in to thinking the aerial is MUCH bigger than it really is ! ) with some RG58 and fit the correct plug to it for your radio ( coax length is not critical )

Cut the antenna to a length of 36cm ( presuming a centre frequency of 200 meg )
What you have done is make the standard antenna in to a 1/4 wave end fed ground plane type
Job done


Bet some of you wish I had never said anything now LOL !!!!!!!
Click to expand...


Impedance - I found this:

"DAB antennas are designed with a 50 S output

impedance instead of the 75 S used for TV and

FM antennas. DAB tuners are fitted with 50 S

BNC connectors to ensure compatibility with

the antenna. For optimum performance a 50 S

low loss coaxial cable should be used between

the antenna and tuner."

From here:

http://www.google.co.uk/url?sa=t&rc...afBke9oUL-la384Hw&sig2=YYwlKWtbKvJ59aCsXqb68w
 
Cheers Tony, so all the above calculations and suggestions are correct then ... had a sneaky feeling it would be 50 Ohms..
Amazingly, I could not find the info but DID manage to find the component list for the pye tank interface used so sussed it out from there ( but my math is not what it used to be !! )
 
Thanks all, will be fitting the radio today and then will look at building the aerial.
 
We have a windscreen mounted "stick on" DAB antenna and it's not actually that bad. It's not 100% but it's many many times better than the FM reception we get. I don't suppose it makes much difference but it's a Pioneer head unit and a Pioneer antenna. I believe that the radio whenever it can, holds the DAB and FM signals for the station at the same time and automatically switches between them to maintain the coverage as much as possible which seems quite a clever trick.
 
Jim, just had a look at that.. Extremely clever design combining 3 different aspects of RF tech.. Love it !
 
Well, finally solved the problem !! And in a very simple manner too.

I bought a £15 magnetic mount DAB aerial from Halfords. Then got a little piece if 3mm steel plate, a little bending and painting then attached it to the top of the awning box. Works a treat !!! Not obscured by anything. Picks up everything all over the Country apart from it dropped out for a few minuets in the depths of Norfolk.

The cable length on the aerial as supplied is 5m and I had to buy a 2m extention to reach the radio. I took the cable in via a cover to the grill (which has been removed) as I am totally adverse to drilling holes in the bodywork when it's still under warrenty.

The photos below should explain all. Just wish there was a need for a few more aerials to go along that rail.

bent metal.JPG aerial.JPG
 
Geordies said:
Well, finally solved the problem !! And in a very simple manner too.

I bought a £15 magnetic mount DAB aerial from Halfords. Then got a little piece if 3mm steel plate, a little bending and painting then attached it to the top of the awning box. Works a treat !!! Not obscured by anything. Picks up everything all over the Country apart from it dropped out for a few minuets in the depths of Norfolk.

The cable length on the aerial as supplied is 5m and I had to buy a 2m extention to reach the radio. I took the cable in via a cover to the grill (which has been removed) as I am totally adverse to drilling holes in the bodywork when it's still under warrenty.

The photos below should explain all. Just wish there was a need for a few more aerials to go along that rail.

View attachment 86827 View attachment 86828
Click to expand...
That's what I did :)

Yorick said:
I just used a cheapy magnetic one from Halfords and put it on the roof :)
Click to expand...
 
NickNic said:
We have a windscreen mounted "stick on" DAB antenna and it's not actually that bad. It's not 100% but it's many many times better than the FM reception we get. I don't suppose it makes much difference but it's a Pioneer head unit and a Pioneer antenna. I believe that the radio whenever it can, holds the DAB and FM signals for the station at the same time and automatically switches between them to maintain the coverage as much as possible which seems quite a clever trick.
Click to expand...

I have a Pioneer Head Unit MVH 270DAB (Deckless Unit No CD deck but has USB,iPod and Android inputs) which Halfords are now selling at £40 !! I have the Halfords Stick-On Windscreen Aerial and get much better reception with this than I did with my previous FM only Unit
On a recent trip from Aberystwyth to Chester I got DAB reception most of the journey The Pioneer Unit switched to FM automatically and back again to DAB during the trip,depending on which signal was available. Doing the same trip before I upgraded to reception on FM alone was much more patchy.

image-jpeg.82200

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