Using non-amplified FM bee-sting aerial for DAB

[Paul Morgan]

I am planning on installing my JVC DAB add-on box in my "new" runaround
car (98 Omega). It has an integrated FM aerial in the rear screen, so no
go with that one for DAB. However it also has a small stubby aerial
body-mounted at the rear of the roof. This, I believe, is for the
integrated car phone kit (which I never intend to use, it relies on the
factory head unit which has been removed).

So I'm thinking of removing this aerial and using the resulting hole in
the roof to mount a DAB aerial. I know I can buy a proper DAB body-mount
aerial, but after seeing the price of them I'm sensing the marketing
machines in overdrive... £40 for what is basically a piece of metal and
some coax cable. Of course it's digital, which justifies the price
entirely as radio waves carrying digital signals are far more fussy than
their analogue counterparts at the same frequency ;-)

I noticed there seems to be very little difference in length of commonly
available roof-mount bee sting FM aerials compared to the DAB aerials.
And unsurprisingly the price is cheaper by a factor of ten! £3 + post,
for example this one: http://tinyurl.com/ln9pm

Obviously I'll need to change the connector to an SMB (but it seems
there are two types of connector common on DAB aerials so I might have
to do that anyway even with a £40 DAB aerial). Are there any other
reasons this aerial won't work well for DAB? It certainly seems like it
should work fine at DAB frequency of ~225MHz and the lack of an
amplifier means that there's no filtering specific to FM frequencies.

Thoughts? Yes I know it's only £40 but why pay such a ridiculous mark-up
if a £3 item will do a similar job?

Cheers
Paul.

[Johnny Turbo]

Post by Paul Morgan
I am planning on installing my JVC DAB add-on box in my "new" runaround
car (98 Omega). It has an integrated FM aerial in the rear screen, so no
go with that one for DAB. However it also has a small stubby aerial
body-mounted at the rear of the roof. This, I believe, is for the
integrated car phone kit (which I never intend to use, it relies on the
factory head unit which has been removed).
So I'm thinking of removing this aerial and using the resulting hole in
the roof to mount a DAB aerial. I know I can buy a proper DAB body-mount
aerial, but after seeing the price of them I'm sensing the marketing
machines in overdrive... £40 for what is basically a piece of metal and
some coax cable. Of course it's digital, which justifies the price
entirely as radio waves carrying digital signals are far more fussy than
their analogue counterparts at the same frequency ;-)
I noticed there seems to be very little difference in length of commonly
available roof-mount bee sting FM aerials compared to the DAB aerials.
And unsurprisingly the price is cheaper by a factor of ten! £3 + post,
for example this one: http://tinyurl.com/ln9pm
Obviously I'll need to change the connector to an SMB (but it seems
there are two types of connector common on DAB aerials so I might have
to do that anyway even with a £40 DAB aerial). Are there any other
reasons this aerial won't work well for DAB? It certainly seems like it
should work fine at DAB frequency of ~225MHz and the lack of an
amplifier means that there's no filtering specific to FM frequencies.
Thoughts? Yes I know it's only £40 but why pay such a ridiculous mark-up
if a £3 item will do a similar job?
Cheers
Paul.

Paul,
Don't buy that £3.00 antenna - there is more to a DAB antenna than looking
the "right length or thereabouts"!!
If you want a cheap(er) solution than a beesting have a look at our website,
follow link to DAB - we do a body mount 1/4 wave flexy antenna with base
that will fit in the hole, and we can supply it with a smb connector.
www.panorama-antennas.com
You can give me a call on our office no. shown on the site if you want
further info.
This is not a sales pitch, but you do need an effective antenna on dab
otherwise you will be dissapointed with the results!!
Cheers, John.

[Paul Morgan]

Post by Johnny Turbo
Paul,
Don't buy that £3.00 antenna - there is more to a DAB antenna than looking
the "right length or thereabouts"!!

I do realise that it's a different frequency (and therefore wavelength),
but other than that what's so special about a DAB antenna compared to
FM? By my reckoning DAB is about double the frequency therefore around
half the wavelength of FM. Aren't most "whip" type FM antennas
quarter-wave, meaning they'd become a half-wave at DAB frequencies?

I understand the basics of antenna theory (at least for the simpler
antennas) so if I'm missing something here please let me know. I do feel
there's a lot of the classic "snake oil" surrounding car DAB antennae
which attempts to justify the otherwise inexplicable price. I can't see
them being any more expensive to manufacture than FM aerials, nor
particularly expensive to design. In addition, home DAB aerials which
look significantly more complex to me, can be purchased for less than
£10! The only real factor I can see in the price is lower volumes
compared to FM antennae, but then how many people buy aftermarket FM
antennae?

Post by Johnny Turbo
If you want a cheap(er) solution than a beesting have a look at our website,
follow link to DAB - we do a body mount 1/4 wave flexy antenna with base
that will fit in the hole, and we can supply it with a smb connector.
www.panorama-antennas.com
You can give me a call on our office no. shown on the site if you want
further info.
This is not a sales pitch, but you do need an effective antenna on dab
otherwise you will be dissapointed with the results!!
Cheers, John.

I realise the limitations of DAB (mostly that it's a highly flawed
implementation hence the signal strength is far too weak in most areas
and the bit-rate too low using an antiquated codec... but that's another
debate entirely ;-) ) hence also realise the need for a decent aerial.
That is why I never bothered installing DAB in my BMW 840Ci, it has no
external aerial at all (integrated rear window FM) so I wasn't going to
drill a hole, and all indications were that glass mount are crap.

How much is your DAB antenna that you mention above? I can't see any
prices on the site. What about the bee-sting DAB listed on the same
page? Jon has pointed out the JVC HAL3 on the other reply which is
around £22, better price but still quite a mark-up over an FM aerial!

Cheers
Paul.

[In-Car Express]

Post by Paul Morgan
Of course it's digital, which justifies the price
entirely as radio waves carrying digital signals are far more fussy than
their analogue counterparts at the same frequency ;-)

DAB isn't at the same frequency - it's significantly higher.

DAB's wavelength is shorter, so you do really need an aerial
specificaly designed for the purpose to get optimum reception. One
cheaper option worth looking at is JVC's HAL3. It sits at a 90 degree
angle, but the mast's only 26cm, so it tends to look OK on the rear
roof on most vehicles (probably worth checking the underhang clearance
before buying one though!). Still more expensive than typical FM
aerials, but about half the price of most roof mounted DAB ones.

Jon

[Paul Morgan]

Post by In-Car Express

Post by Paul Morgan
Of course it's digital, which justifies the price
entirely as radio waves carrying digital signals are far more fussy than
their analogue counterparts at the same frequency ;-)

DAB isn't at the same frequency - it's significantly higher.

I do realise that, but my thinking is that DAB is around double the
frequency (at least the DAB band used in the UK) therefore a
quarter-wave FM aerial should become a half-wave at DAB frequencies.
Neither aerial will be focussed to a narrow frequency since they both
have to cover a range of about 20MHz so even if it's not exactly double
there should still be plenty of leeway before the antenna performance
becomes poor.

Correct me if I'm wrong on this ;-)

Post by In-Car Express
DAB's wavelength is shorter, so you do really need an aerial
specificaly designed for the purpose to get optimum reception. One
cheaper option worth looking at is JVC's HAL3. It sits at a 90 degree
angle, but the mast's only 26cm, so it tends to look OK on the rear
roof on most vehicles (probably worth checking the underhang clearance
before buying one though!). Still more expensive than typical FM
aerials, but about half the price of most roof mounted DAB ones.

Thanks, the HAL3 looks *almost* reasonably priced... but when you can
manufacture and sell FM aerial for £3 it gives an idea of the mark-up
(by the manufacturers moreso than the retailers) ;-)

I assume the HAL3 is a quarter-wave then at 26cm? Many of the others
I've seen (particularly the inductively-coupled glass mounts) have been
around 45cm - I assume those are half-wave and should give a lower loss?
Is the reason for this being used on the glass-mount to overcome some of
the loss due to the inductive coupling?

Saying that 45cm is probably too big to be putting as a roof-mount,
that's asking for trouble!

Cheers
Paul.

PS By my calculation DAB with a centre frequency of 220MHz will have a
wavelength of 1.36 metres... therefore a quarter-wave will be ~34cm
including the base (and possibly some kind of effect of the cable,
although surely not shielded coax? Confused!)

[In-Car Express]

Post by Paul Morgan
Thanks, the HAL3 looks *almost* reasonably priced... but when you can
manufacture and sell FM aerial for £3 it gives an idea of the mark-up
(by the manufacturers moreso than the retailers) ;-)

One of the biggest problems up to now is the low volumes involved.
Manufacturers like JVC, Sony, etc tend not to produce the parts
themselves, as the market's not big enough to warrant it, so there's
an extra step in the chain, with the associated cost.

Yes, you can buy an FM antenna for £3, but it'll be a cheap, poorly
made one. At this point in time, DAB aerials tend to be much better
made - JVC's look as though they could well be made by Hirschmann.
Hirschmann's FM aerials generally cost as much as, if not more than,
typical DAB aerials.

Post by Paul Morgan
Many of the others
I've seen (particularly the inductively-coupled glass mounts) have been
around 45cm - I assume those are half-wave and should give a lower loss?

All of the exterior glass mounts we've seen have been stupidly long
(to the point that the bases never seem to stay stuck down) and not
especially good with it. The interior type (HAL1/DFA1 or Sony's
supplied one with the DAB6650) seem pretty good though and more than
adequate with the signal levels around here.

Jon

[Colin Stamp]

Post by Paul Morgan
I am planning on installing my JVC DAB add-on box in my "new" runaround
car (98 Omega). It has an integrated FM aerial in the rear screen, so no
go with that one for DAB. However it also has a small stubby aerial
body-mounted at the rear of the roof. This, I believe, is for the
integrated car phone kit (which I never intend to use, it relies on the
factory head unit which has been removed).
So I'm thinking of removing this aerial and using the resulting hole in
the roof to mount a DAB aerial. I know I can buy a proper DAB body-mount
aerial, but after seeing the price of them I'm sensing the marketing
machines in overdrive... £40 for what is basically a piece of metal and
some coax cable. Of course it's digital, which justifies the price
entirely as radio waves carrying digital signals are far more fussy than
their analogue counterparts at the same frequency ;-)
I noticed there seems to be very little difference in length of commonly
available roof-mount bee sting FM aerials compared to the DAB aerials.
And unsurprisingly the price is cheaper by a factor of ten! £3 + post,
for example this one: http://tinyurl.com/ln9pm
Obviously I'll need to change the connector to an SMB (but it seems
there are two types of connector common on DAB aerials so I might have
to do that anyway even with a £40 DAB aerial). Are there any other
reasons this aerial won't work well for DAB? It certainly seems like it
should work fine at DAB frequency of ~225MHz and the lack of an
amplifier means that there's no filtering specific to FM frequencies.
Thoughts? Yes I know it's only £40 but why pay such a ridiculous mark-up
if a £3 item will do a similar job?
Cheers
Paul.

It's not just the frequency that's different. I get the impression
that the field-strength is a lot weaker for DAB too, so you do need a
high quality aerial to make sure you're not wasting any precious dBs
on a crummy downlead or whatever.

You can get splitters that attempt to give you a DAB signal from an FM
aerial, but others have said the performance is crap.

I've got a Pioneer, amplified roof-mount DAB aerial on my car and I
get two muxes reliably in Milton-Keynes. I'm not sure if that's good
or not...

Cheers,

Colin.

[Paul Morgan]

Post by Colin Stamp
It's not just the frequency that's different. I get the impression
that the field-strength is a lot weaker for DAB too, so you do need a
high quality aerial to make sure you're not wasting any precious dBs
on a crummy downlead or whatever.

Fair enough, but I don't see anything on most of these passive antennae
that would make them perform better than their FM equivalents.

Post by Colin Stamp
You can get splitters that attempt to give you a DAB signal from an FM
aerial, but others have said the performance is crap.

I'd expect so, splitting a passive signal isn't a particularly good idea
at the best of times, let alone from an aerial that isn't ideal at that
frequency. Both my cars have active rear-screen aerials so that's not an
option (not that I'd have gone down that route anyway).

Post by Colin Stamp
I've got a Pioneer, amplified roof-mount DAB aerial on my car and I
get two muxes reliably in Milton-Keynes. I'm not sure if that's good
or not...

Mine is a JVC add-on box, and it came with a passive stick-on roof
aerial that I used on my old Audi which worked most of the time, but it
dropped out going under extended motorway bridges that barely affected
FM reception. It's pretty obvious the DAB signal strength is woefully
inadequate for reliable reception in the presence of obstructions,
significantly worse than FM. Coupled with the poor bitrates and even
worse codec it's no wonder the adoption rate is so poor - I'd say it's
now a dying technology and will probably remain a niche product until a
successor comes along.

Back on topic, a through-roof mount should provide at least as good a
signal as the supplied aerial due to the ground plane, and an amplified
aerial wouldn't benefit my DAB box as it's not designed for one
(probably does some internal amplification). I might just go for one of
the "proper" DAB aerials as suggested by the other posters in this
thread, begrudgingly forking out the £20-something - still a lot better
than the common price which is closer to £40!

Paul.

[Colin Stamp]

Post by Paul Morgan

Post by Colin Stamp
It's not just the frequency that's different. I get the impression
that the field-strength is a lot weaker for DAB too, so you do need a
high quality aerial to make sure you're not wasting any precious dBs
on a crummy downlead or whatever.

Fair enough, but I don't see anything on most of these passive antennae
that would make them perform better than their FM equivalents.

Post by Colin Stamp
You can get splitters that attempt to give you a DAB signal from an FM
aerial, but others have said the performance is crap.

I'd expect so, splitting a passive signal isn't a particularly good idea
at the best of times, let alone from an aerial that isn't ideal at that
frequency. Both my cars have active rear-screen aerials so that's not an
option (not that I'd have gone down that route anyway).

Post by Colin Stamp
I've got a Pioneer, amplified roof-mount DAB aerial on my car and I
get two muxes reliably in Milton-Keynes. I'm not sure if that's good
or not...

Mine is a JVC add-on box, and it came with a passive stick-on roof
aerial that I used on my old Audi which worked most of the time, but it
dropped out going under extended motorway bridges that barely affected
FM reception. It's pretty obvious the DAB signal strength is woefully
inadequate for reliable reception in the presence of obstructions,
significantly worse than FM. Coupled with the poor bitrates and even
worse codec it's no wonder the adoption rate is so poor - I'd say it's
now a dying technology and will probably remain a niche product until a
successor comes along.

You might well be right, but there's a few years in it yet. If they
replace it, I expect the codec will improve but the bitrates will
probably get lower still. They've already decided that the number of
services is more important than the sound quality.

Post by Paul Morgan
Back on topic, a through-roof mount should provide at least as good a
signal as the supplied aerial due to the ground plane, and an amplified
aerial wouldn't benefit my DAB box as it's not designed for one
(probably does some internal amplification). I might just go for one of
the "proper" DAB aerials as suggested by the other posters in this
thread, begrudgingly forking out the £20-something - still a lot better
than the common price which is closer to £40!

Yep. The ground-plane made a huge difference on mine. My JVC head-unit
could barely pick anything in the shed when I tried it out with the
Pioneer aerial un-mounted. It was much better when I clamped it to the
side of a foot-square ally sheet. It's fine in the car.

I agree that an amplified one isn't for you though. With no power, the
amplifier will attenuate the signal, so it'll be much worse than a
passive one.

Cheers,

Colin.