Ok, where is my radio antenna?

[DanH]

Was told it was in the wheel arch (I don't have a roof mounted one), but I can't find it and it needs remedial work.

[mikes_3r]

Maybe that's the issue.


(sorry couldn't resist)

[joust]

It's down in the passenger side front wheel arch.

Put your hand on top of the front tyre, now move it inwards horizontal until you hit the vertical upright sheet and it's attached to that.

You can clearly see it in this photo, pointing downwards from the bulkhead going behind the air con reservoir.

www.lotus-elise.org.uk/m12/P1010485.JPG

J

[m12_nathan]

Mine is above the passenger sun visor inside the cabin.

[DanH]

m12_nathan said:

Mine is above the passenger sun visor inside the cabin.

Hmm I suspect mine may be too then since its not in the wheel arch as per that pic I don't think.

[Richard Marshall]

Dan,

If it's not picking up anything worth listening to
i.e. only got radio 1
Give Vegantune a ring and Paul will explain:
a/ the principles of the Ferreday cage
b/ arrange the fitting of an aerial that works.

mikes_3r said:

Maybe that's the issue. (sorry couldn't resist)

[m12_nathan]

Or just put a cd on

[joust]

Richard Marshall said:

a/ the principles of the Ferreday cage

Faraday

The car isn't really a Faraday cage, the main problem is the standard one doesn't have any ground plane connection, and hence the antenna has no "counterpoise". Without that, you have three choices.

1) Find a suitable mass of metal. The front or rear sheet structure is pretty good, but given you need the antenna close to it's counterpoise, you struggle to find a place that works.

2) Put another piece of wire at 90 degrees to the antenna that is a full, 1/2 or 1/4 wavelength long (about 10 feet for a full wavelength). That will act as it's counterpoise - you can often see these in DAB antennas nowdays. It's suprisingly effective....

3) Ignore both and just amplify the unmatched antenna's signal - it's the brute force way, but suprisingly effective if you use a 1/4 wavelength antenna.

Modwise do a combined 2) and 3) [www.mod-wise.com/page2.html] that works very well.

J

[DanH]

I was considering going for one of these :

Details:
Product model number: Metra 44UA20.
FEATURES:
High gain Hide-away amplified antenna or AM/FM bands
Active magnetic-type antenna, working on the magnetic field associated with a conductor excited by a microwave
Voltage pickup is Nanovolts, but with the magnetic type circuitry it extracts a signal with a superior signal-to-noise ratio
102 in./260 cm coaxial cable and power supply wire


Why does an antenna need a ground plane? I have portable radios with better reception and no big sheet metal in them. Presumably the chassis is used as an earth anyway?

As far as I can see the main thing noble did on later cars was to put the aerial on the roof?

Richard - I'd be happy if I could even get Radio 1!

[MisterX]

DanH said:

I'd be happy if I could even get Radio 1!

I can only get AM, not FM, and only Five Live has a listenable reception (on 909 wavelength).
Allegedly an internal aerial, but you try finding it!

[joust]

DanH said:

I was considering going for one of these : Details: Product model number: Metra 44UA20. FEATURES: High gain Hide-away amplified antenna or AM/FM bands Active magnetic-type antenna, working on the magnetic field associated with a conductor excited by a microwave Voltage pickup is Nanovolts, but with the magnetic type circuitry it extracts a signal with a superior signal-to-noise ratio 102 in./260 cm coaxial cable and power supply wire

Hmm - it might work (apart from the mumbo jumbo about how it works, at a rough guess its a ferrite core with a helix antenna), but it probably still needs mounting next to something metallic, and that'll be your problem.

DanH said:

Why does an antenna need a ground plane? I have portable radios with better reception and no big sheet metal in them. Presumably the chassis is used as an earth anyway?

Because of what I wrote above. Your portable actually either will use the ground plane dipole ala 2), or more likely, will use the earth plane of the PCB as it's ground plane. I've designed similar PCBs in my youth and it works quite well if you have a 1/4 or 1/8th antenna.

Mobile phones use similar, or they use a helix antenna which reduces the need for a ground plane. Unfortunatly helix's aren't very good for FM (which is why I'd be a little bit suspisious about that Metra thing - but for $40 it might be worth a go).

DanH said:

As far as I can see the main thing noble did on later cars was to put the aerial on the roof?

Yes - and it helps things by just being higher. The AGC in the head end can then use 3) above to get a decent signal. It's still not great though, but gives good Radio 2 coverage along Motorways.

I'll be mounting my DAB antenna in a few weeks and I'll then put up a guide about how to get a decent signal.

J

[DanH]

I was considering dab, but think I may go for one of those cheap hard disk based head units, whose manufacturer I've forgotten. Its cheaper than an alpine head and ipod link unit... Probably worse too Alpine DAB is criminally expensive though.


How do glass mount FM antenna work then? Just big amplification?

[DanH]

I did have an aftermarket grounding plate in my Elise which worked pretty well but unfortunately only when the engine was off. As soon as it was turned on, it went crappy. Presumably because the radio aerial was right above the HT leads & plugs which aren't famed for their lack of EMR.

[Richard Marshall]

DanH said:

I did have an aftermarket grounding plate in my Elise which worked pretty well but unfortunately only when the engine was off. As soon as it was turned on, it went crappy. Presumably because the radio aerial was right above the HT leads & plugs which aren't famed for their lack of EMR.

Dear DanH

O.k. I have read ALL the correspondence and my head hurts a lot now.
Please allow me to repeat option B/
If you would like an aerial that works please give us a call at Vegantune and we will supply and fit one for you for FREE
It may make my headache go away.
And I promise not to tell you why it works...it just does and THAT is what matters is it not?

Richard

[DanH]

Richard Marshall said:

DanH said: I did have an aftermarket grounding plate in my Elise which worked pretty well but unfortunately only when the engine was off. As soon as it was turned on, it went crappy. Presumably because the radio aerial was right above the HT leads & plugs which aren't famed for their lack of EMR. Dear DanH O.k. I have read ALL the correspondence and my head hurts a lot now. Please allow me to repeat option B/ If you would like an aerial that works please give us a call at Vegantune and we will supply and fit one for you for FREE It may make my headache go away. And I promise not to tell you why it works...it just does and THAT is what matters is it not? Richard

Thank you very much As to the discussion, I just like to know why things work! Not to mention I need to add a splitter on to the aerial for a gps thingy I've ordered, and quality of signal is apparently very important.

Thats the problem with cars popular with techies, we all want to know 'why?' the whole time

[Richard Marshall]

DanH said:

Richard Marshall said: DanH said: I did have an aftermarket grounding plate in my Elise which worked pretty well but unfortunately only when the engine was off. As soon as it was turned on, it went crappy. Presumably because the radio aerial was right above the HT leads & plugs which aren't famed for their lack of EMR. Dear DanH O.k. I have read ALL the correspondence and my head hurts a lot now. Please allow me to repeat option B/ If you would like an aerial that works please give us a call at Vegantune and we will supply and fit one for you for FREE It may make my headache go away. And I promise not to tell you why it works...it just does and THAT is what matters is it not? Richard Thank you very much As to the discussion, I just like to know why things work! Not to mention I need to add a splitter on to the aerial for a gps thingy I've ordered, and quality of signal is apparently very important. Thats the problem with cars popular with techies, we all want to know 'why?' the whole time

O.K. Hands up Me personnaly I dunno why.
However Paul (Vegantune's operations director) who amongst other things is a "new clear fizzy cist" (see I can't even spell it).
Does understand and understands it so well he can even explain things to me.
Will tell you.
Give him a call tomorrow (I may not be at work as I will still be in my happy place trying to shake off this headache)

Richard

[joust]

Richard Marshall said:

O.K. Hands up Me personnaly I dunno why. However Paul (Vegantune's operations director) who amongst other things is a "new clear fizzy cist" (see I can't even spell it). Does understand and understands it so well he can even explain things to me. Will tell you. Give him a call tomorrow (I may not be at work as I will still be in my happy place trying to shake off this headache)

Sorry Richard - I'll shut up and stop your head hurting hopefully!

I'm sure your solution works well, I just thought a few people might like to know some of the "physics" behind it.

J