60six
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Sept 16, 2020 7:36:43 GMT
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Have always wondered why DAB needs a separate aerial - Always a pain to fit neatly and I thought totally unnecessary as they could of used the existing FM aerial. Found this on eBay and it works a treat. No more DAB aerial fitting!  |
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Some 9000's, a 900, an RX8 & a beetle
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Jem45
Posted a lot
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Sept 16, 2020 8:04:14 GMT
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Potentially interesting. Have you got a link?
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Carbs 'n chrome
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Sept 16, 2020 8:04:45 GMT
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We run a car audio and security shop and have tried all sorts of adapters and none of them really work. Glass mount aerial in the front screen is by far the best option.
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Its not broken, its resting!
Max signature image height: 80px
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Sept 16, 2020 8:39:19 GMT
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I used one of those to like my 60s aerial to my dab radio and it works great. Even in the wilds of Wales. Never had any reception problems at all.
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Sept 16, 2020 9:58:52 GMT
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so what actually is (or what is the assumed obsolescence) between dab aerial and the old one?
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Sept 16, 2020 11:02:00 GMT
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so what actually is (or what is the assumed obsolescence) between dab aerial and the old one? I have no idea! |
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awoo
Posted a lot
Posts: 1,503
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Sept 17, 2020 19:47:52 GMT
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You can fit a regular dab aerial under the bumper. Works fine there and completely out of sight.
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Sept 17, 2020 21:17:51 GMT
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It won’t matter what aerial you use dab in a car is pants. It just goes off when it feels like it, the reception is curse word. I’m sure it probably works fine in the middle of London, but in Derbyshire it’s curse word
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Sept 17, 2020 21:40:26 GMT
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Very roughly - an aerial works by being tuned to the wavelength of the signal it's trying to pick up. (Actually all 'radio frequency' engineering is just black magic and I've never really understood a word of it.)
FM radio is around 100Mhz and DAB is up at around 220Mhz so to get the best out of it you need a different length aerial. I wouldn't be at all surprised if the polarisation was different too.
The wire in the photo would appear to be one socket paralleled to two plugs. There is a thing called 'characteristic impedance' in an RF system. For radio and TV it's generally 75 ohms. So the input to the receiver, the cable, the aerial and probably even the atmosphere are all 75 ohms and everything is happy.
The wire shown above means the aerial now sees two receivers - 37 ohms - and signals will bounce up and down the cable.
The only way they could have avoided this problem is if they frequency split the signal so below, say, 150Mhz it's sent to the FM tuner and above it goes to the DAB tuner. But the lead isn't big enough for the bits so they didn't!
All in all it's a disastrous idea and will never work. The fact that is does is because it's all just black magic.
James
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60six
Posted a lot
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Posts: 1,658
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Sept 18, 2020 21:53:32 GMT
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Some 9000's, a 900, an RX8 & a beetle
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Sept 18, 2020 22:34:25 GMT
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The wire in the photo would appear to be one socket paralleled to two plugs. There is a thing called 'characteristic impedance' in an RF system. For radio and TV it's generally 75 ohms. So the input to the receiver, the cable, the aerial and probably even the atmosphere are all 75 ohms and everything is happy. The wire shown above means the aerial now sees two receivers - 37 ohms - and signals will bounce up and down the cable. It will have a couple of resistors in series to get the impedance right at all three ends. Really cheap TV aerial splitters were like this too. Slightly more upmarket ones would have a little transformer inside. Still all passive but just a little bit better. As you say, an FM aerial is the wrong length for DAB. But if your in an area with good coverage it won't matter much. |
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