Don't buy DAB car radios!

musa

I recently replaced my car radio and thought I would try to be a little future proof and buy a DAD radio.
Maplin in Belfast sold me a very respectable radio/CD/DAB radio around 100
Euro (no S).
No signal was received on DAB even when I could see Divis transmitter,never mind "Line of sight".
Maplin rang around and concluded that the problem was the motorised car aerial,and one could be sourced that woud sit on the dash,for seventy Euro.
It is a fine radio with good FM quality,CD slot ,only when front of radio is folded down,couldn't find the slot for some time.
Halford stores claim that when you buy DAB car radios from them,the kit should contain an aerial,but you could be talking four times the price of the Maplin set.
The older gents in our midst may recall a relationship between frequency,wavelength and the speed of light,enabling one to calculate the aerial length ,and maybe make your own?,but try talking to the computer heads in the stores about such matters.
Anyway buy all the DAB you like ,but beware if its the car you intend to use
DAB in be careful or wait for 2012 when the wind the wick up.

Radio|Man

All DAB aerials (should) come with an antenna. The most common type being an adhesive strip you tape to the front or rear windscreen.

DAB requires vertically polarised elements, FM horizontally polarised.

Using your existing FM aerial will simply not work for these reasons as well as it being a totally different wavelength.

Perhaps you might GOOGLE before posting such sensationalist remarks

L1011

Title should be "don't buy DAB car radios in Maplin". You ALWAYS need a new aerial unless you live in an insanely high signal area, due to the massive difference in frequency from FM (88-108Mhz vs. 174-239Mhz).

Now, I'm listening to FM on a DAB antenna here right now but thats just working in the "massive lump of metal" way of things....

Ulsterman 1690

DAB requires vertically polarised elements, FM horizontally polarised

All FM broadcasts in the UK* have been using either vertical or mixed polorisation since the 1980's

I have yet to see a car with a horizontally polorised radio aerial (kinda hard to imagine how such a thing would work properly)

* Licenced FM broadcasts in the Republic of Ireland have always been either vertical or mixed

DMC

Ulsterman 1690 wrote: »

I have yet to see a car with a horizontally polorised radio aerial

Coat hangers!

Ulsterman 1690

Ummmm you got me there

musa

Ulsterman 1690 wrote: »

All FM broadcasts in the UK* have been using either vertical or mixed polorisation since the 1980's

I have yet to see a car with a horizontally polorised radio aerial (kinda hard to imagine how such a thing would work properly)

* Licenced FM broadcasts in the Republic of Ireland have always been either vertical or mixed

Thanks for the interest shown by all,I think I recall Classic FM was pushing the notion that it was the first UK station to transmit in circular polorisation for reception in cars.The radio in question is a Centurion professional,great FM quality so maybe I should be satisfied with that for now.What is the wavelength for a DAB radio aerial?
Sorry for being "Sensational",but hey it got a response but no answer.
Not all DAB radios come with an aerial,thats all I was saying beware.

musa

MYOB wrote: »

Title should be "don't buy DAB car radios in Maplin". You ALWAYS need a new aerial unless you live in an insanely high signal area, due to the massive difference in frequency from FM (88-108Mhz vs. 174-239Mhz).

Now, I'm listening to FM on a DAB antenna here right now but thats just working in the "massive lump of metal" way of things....

Several very good points,thanks for the freq info,its a fine radio at a quarter the price ,sure we shouldn't be put off for the lack of a piece of wet string .
We may soon have to consider the "Skin effect" if we keep upping the frequency.(Joke)

musa

Radio|Man wrote: »

All DAB aerials (should) come with an antenna. The most common type being an adhesive strip you tape to the front or rear windscreen.

DAB requires vertically polarised elements, FM horizontally polarised.

Using your existing FM aerial will simply not work for these reasons as well as it being a totally different wavelength.

Perhaps you might GOOGLE before posting such sensationalist remarks

Not so sure about your comment re polarised FM.
Anyway rang Maplin "Technical Helpline",man told me to use the existing car aerial,I passed on the Boards comments and told him I should be charging him BT premium line rates.
If we all GOOGLED why would we use the Board?,surely we all learn from dialouge,even if we upset a few on the way.

watty

Using existing FM (Band II) aerial will work if it is any good. The stupid bee sting 3" or 4" won't, they are rubbish any way.

Almost all existing car aerials are vertical polarised (excpetion is a strip across windscreen or rear heater, both are rubbish compared with external Whip). Some coax cables that improve MW & LW have a coiled centre core. These are poor on VHF -FM band II and poorer on BandIII DAB.

I have a 1/4 wave VHF Band II aerial on roof and it gets BBC VHF FM as far south as Collon, at least. The Band III Dab is simply poor power level and not as good mobile as VHF-FM. If you have a full size VHF-BandII FM whip (about 75cm long?) you can cut about 1/3rd off it as a compromise to improve DAB reception at expense of DAB. It's possible to have a Dual Band aerial (a small coil in middle makes it act as two stacked aerials on BandIII and a single whip on Band II). But a decent BandII VHF-FM aerial will work fine for DAB, just about 1/2 the range.

musa

watty wrote: »

Using existing FM (Band II) aerial will work if it is any good. The stupid bee sting 3" or 4" won't, they are rubbish any way.

Almost all existing car aerials are vertical polarised (excpetion is a strip across windscreen or rear heater, both are rubbish compared with external Whip). Some coax cables that improve MW & LW have a coiled centre core. These are poor on VHF -FM band II and poorer on BandIII DAB.

I have a 1/4 wave VHF Band II aerial on roof and it gets BBC VHF FM as far south as Collon, at least. The Band III Dab is simply poor power level and not as good mobile as VHF-FM. If you have a full size VHF-BandII FM whip (about 75cm long?) you can cut about 1/3rd off it as a compromise to improve DAB reception at expense of DAB. It's possible to have a Dual Band aerial (a small coil in middle makes it act as two stacked aerials on BandIII and a single whip on Band II). But a decent BandII VHF-FM aerial will work fine for DAB, just about 1/2 the range.

Shall read all of the above and hope to digest without recourse to GOOGLE.
I seem to recall that the appliance of inductance can shorten an aerial?
In the dying days of annalouge mobile phones , some folk used wide band tv amps to boost car reception?
The whole thing seems to be a problem on the DAB horizon worth considering,if you want to drive around ,listening ,and I am told seeing adverts on your car radio.Test results to follow.many thanks to all,even grumpy wireless cats whiskers,Happy Christmas.

gerryo

Ulsterman 1690 wrote: »

All FM broadcasts in the UK* have been using either vertical or mixed polorisation since the 1980's

I have yet to see a car with a horizontally polorised radio aerial (kinda hard to imagine how such a thing would work properly)

* Licenced FM broadcasts in the Republic of Ireland have always been either vertical or mixed

I saw a picture of one in a very old radio/TV book, if you can imagine taking a folded dipole & bending it in a circle, that's what a horizontally polarised car aerial looked like.

Looked too cumbersome to be practical.

Radio|Man

musa wrote: »

Not so sure about your comment re polarised FM.
Anyway rang Maplin "Technical Helpline",man told me to use the existing car aerial,I passed on the Boards comments and told him I should be charging him BT premium line rates.
If we all GOOGLED why would we use the Board?,surely we all learn from dialouge,even if we upset a few on the way.

Sorry, I forgot to mention that I am filthy stinking rich and would only drive a motor vehicle with built in rear screen, vertically polarised antenna.

The cheaper the head unit, the worse the antenna gain appears to be from my experience.

Have a read of this

http://www.smartradio.sg/reception.htm

musa

Radio|Man wrote: »

Sorry, I forgot to mention that I am filthy stinking rich and would only drive a motor vehicle with built in rear screen, vertically polarised antenna.

The cheaper the head unit, the worse the antenna gain appears to be from my experience.

Have a read of this

http://www.smartradio.sg/reception.htm

Thank you for the info.

Antenna

watty wrote: »

Using existing FM (Band II) aerial will work if it is any good. The stupid bee sting 3" or 4" won't, they are rubbish any way.

most modern cars use a short aerial (beesting etc) with a built in amplifier, and this amplifier is designed for VHF 87.5-108 only as well as MW/LW. The amplifier is the main reason why DAB will not work with existing aerials, its like trying to use a Band III TV masthead amp for UHF .

BTW the main problem with beestings at FM in not the length, but often being at a 45 degree approx angle. At that angle multipath distortion is much worse compared to a vertical aerial.

watty

If they have to amplifiy it that PROVES the short bee stings are rubbish. Replace aerial with at least 0.5m whip and no amp.

Modern radios are quite sensitive enough. On mine I can get Limerick 95FM from PortLiose. (no amplifier, plain whip on roof).

It seems that marketing departments have won out over common sense on design of newer cars.

byte

BMW's don't even seem to have a beesting, but a sort of fin at the back. Not sure how effectirve or not these are. Maybe it's unrelated to the radio, and is something else...

SimonMaher

Hello all. On the topic of DAB car radios, I managed to pick up a nifty little one for under 100 quid from Goodmans Direct. I was amazed how good it was for the price I paid. Plugged it all in (It has CD/MP3 and decent FM and AM coverage too) and it is connected to the 18 inch metal aerial on the car (bought for about 12 quid - its a bosch). DAB coverage is remarkably consistent with it, even around the city centre. Really is only in the depths that it breaks up. Im well impressed with it!

Simon

watty

byte wrote: »

BMW's don't even seem to have a beesting, but a sort of fin at the back. Not sure how effectirve or not these are. Maybe it's unrelated to the radio, and is something else...

it's so the bathers know to get out of the water quick. I'd assumed those are also a rubbish amplified aerial.


I have a decent dual band aerial for 29MHz/50Mhz on the car. It's big. But worse than a bee sting on VHF for 1.8MHz. I can tune up my Military transmitter on it at 1.8MHz, for which the aerial is 20 times too small, but at that frequency a 1/4 wave would be 40m tall (132ft or 5 times height of house). At VHF there is no excuse. A 1/4 wave is only 75cm. Even a 60cm will work very well. That's only 2ft. A mere nothing. For DAB a full 1/4 wave is about 40cm to 50cm. Cutting 1/3rd off a full 1/4 wave whip for Band II VHF-FM will improve DAB signal and it will still work better than a "bee sting"/"shark fin" for VHF-FM Band II.