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Old 6th June 2007, 14:55   #31
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Originally Posted by santosh.s View Post
To make it work reasonably across the whole FM band, antennae are tuned to the frequency corresponding to the center of the band.

Making an FM antenna is probably the easiest DIY... but wouldn't it look plain ugly?

Another doubt, since glass antenna is surrounded by metal all around (worst in case of defoggers), wouldn't it deteriorate it's performance?
hi,

how do you tune an FM antenna?

i will stick it on the front windscreen. would rather diy than spend 5600 on an fm antenna. but if the after market antenna works fine then no need to diy. BTW, are the after market power antennas reliable(the motor)? hope it doesn't conk off too often.

cheers
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Old 6th June 2007, 15:02   #32
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Well you change the length.
So if you are on a 3 meter wave, you use a 1.5 meter long dipole, If your antenna length is shorter, it will cater to higher frequencies. You just need to follow the 468/(Frequency in MHz) rule and select length. For all frequencies, choose one bang in middle 468/98 - 5%
If you want the complete maths, then I will have to guide you to 6 month semester in "antenna theory and applications" which is used to torture Electronics engineering students. Believe me I suffered through it. My analog designer friends are still suffering, so are poor board designers.
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Old 6th June 2007, 16:25   #33
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Originally Posted by tsk1979 View Post
Well you change the length.
So if you are on a 3 meter wave, you use a 1.5 meter long dipole, If your antenna length is shorter, it will cater to higher frequencies. You just need to follow the 468/(Frequency in MHz) rule and select length. For all frequencies, choose one bang in middle 468/98 - 5%
If you want the complete maths, then I will have to guide you to 6 month semester in "antenna theory and applications" which is used to torture Electronics engineering students. Believe me I suffered through it. My analog designer friends are still suffering, so are poor board designers.
thanks tsk. will see if the after market antenna works fine. if not, then ill try the above method.

OT - why, is engineering a torture? i would love to do it. what is the criteria for admission? can i do it through correspondence? or is there a shorter course on electronics which i can do? let me know please. i didnt take my studies seriously and im suffering. now im damn serious and willing.

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Old 6th June 2007, 16:35   #34
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clip, one reputed institute offering correspondence courses in engg that I know of is BITS Pilani (Rajasthan). Have a look at About BITS Distance Learning Programmes
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Old 6th June 2007, 16:54   #35
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clipto, what do you do now? Business etc.,? A good option for a technically inclined person like you would be to do a diploma in electronics. I think the NIT in your town will offer that course. Its a 1 year long course and will teach you the practical side.
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Old 6th June 2007, 16:56   #36
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Busa, the Little Shark in BMW's and Merc's looks great. Is it possible to get the same thing installed in swift?


Pic Taken from Cardomain.
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Old 6th June 2007, 17:24   #37
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shark fin antenna for FM/AM.
Its too small to give any benefit. With or without you will get same reception. Shark fin antennas are actually used for XM and Sirius Satellite radio services. The wavelength is very small there.
So unless mobile satellite radio comes here, it won't be very useful.
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Old 6th June 2007, 17:26   #38
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OT - why, is engineering a torture?
Grass on the other side is always greener. Just finished giving my final year exams. I think its torture because the education system in India doesn't allow you to have major and minor subjects, we can only select streams. So sometimes you end up 2 subjects per semester which doesn't interest you. And its real pain in a$# to pass in those subjects.

I remember in 2003 I went with my dad to Chandigarh in Lancer (Chandigarh is 270 kms from Delhi). It had OEM antenna and we received FM till 30-20 kms from chandigarh's border. After that it died down.
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Old 6th June 2007, 17:42   #39
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I have a Blaupunkt, better than the local unknown ones in terms of performance, still can't come close to proper antennas.
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Old 6th June 2007, 19:36   #40
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tsk, you seem to have good understanding of antenna theory... so, more questions...

- the folded dipole antenna that you suggested is directional, right? then it should NOT be suitable for mobile application? Even for home use, it depends upon locations of various stations (you may need to change the direction when you change stations).

Based on whatever I know, I do have some idea as to what might be a better antenna- Vertical, long antenna, minimum of about 5ft for FM (essentially translates to external motorized one) because all others are shorter than the minimum requirement. Also, it is desirable to have a plain horizontal conducting surface just below the vertical dipole as it creates a mirror image and virtually doubles the effective length. I think mounting at the center of the roof would be ideal, but all of them are mounted on the boot. However, I am not really an expert, so wanted to check with people who might understand theoretical or practical, or even better- both aspects in depth.

Do you agree that all shorter varieties should be inferior to motorized vertical dipole?

What about rabbit ear glass antenna... these too?

Backward tilting makes sense to reduce permanent damage due to bending by air resistance. but does it have any disadvantages (or advantages) in terms of reception? do we have to increase the length to compensate for tilting?

Major issues in reception are-
1. picking up weak, long distance stations
2. being insensitive to reflections in cities

Are these different antennae particularly suitable or unsuitable for dealing with above mentioned problems?

Does polarization matter for FM radio?

Sorry, I have made it too technical, but I am sure answers to these questions will be quite useful (practically!) to all of us.

Last edited by santosh.s : 6th June 2007 at 19:39.
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Old 7th June 2007, 00:02   #41
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Yes its directional, but directional does not mean it will work in only one direction, it means that gain in one direction is maximum. So when car is oriented in the less favourable direction, you will have less gain, but local FM broadcasters broadcast pretty strong, thats why even a single wire will do.

The long antennas which you see on cars(motorized or normal) are variations of J-Pole(Also called north pole) antenna. Thats a omnidirectional antenna, but makes aesthetics suffer.
Rabbit year is similar to a dipole, but the gain reduction in non favorable direction is less. Old TVs has this, and remember you had to turn it to get reception.
The best way to get a omnidirectional FM antenna is to have a turntable antenna. i.e. 2 dipole antennas perpendicular to each other, but that works in a house, but not in a car.

From a purely practical point of view
1. Motorized long antennas are really good
2. Windshied dipole antennas are not good, because manufacturers use just 1 feet long antenna instead of 4-5 feet.
3. DIY dipole antenna will give better performance
4. The shark fin antenna is good for satellite radio(not available in india), but FM reception with or without that will be similar
5. Rear defroster antenna is good as long as defroster is not on.

As for tilting etc., nope, the length should be the same as decided by the equation, it will just effect gain.
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Old 7th June 2007, 07:34   #42
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Which are the other Indian cars having Glass antenna ?
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Old 7th June 2007, 13:51   #43
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Quote:
Originally Posted by mithun View Post
Which are the other Indian cars having Glass antenna ?
In the order it was seen in cars.

Optra
Elantra
Corolla
Aveo
Civic
SX4
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Old 7th June 2007, 14:48   #44
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tsk, that was pretty useful information!

A couple of questions are still open though...
1. Reflections. I know high end receivers from pioneer, jvc have dedicated circuits in their tuners to filter them out. But was wondering if there are any related tips regarding the antenna itself.

2. Polarization. does it matter? was wondering if that would call for any additional care to be taken in antenna orientation. Hope not.

Quote:
Originally Posted by tsk1979 View Post
Yes its directional, but directional does not mean it will work in only one direction, it means that gain in one direction is maximum.
That obviously means that reception will be worst in minimum gain position. I thought that it will be even worser than a short wire, no? For example, if you are driving in city outskirts, reception will be good if station happens to be right in front of you or back side. But it will be bad when the station is exactly on either left or right side.
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Old 7th June 2007, 15:02   #45
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Quote:
Originally Posted by santosh.s View Post
tsk, that was pretty useful information!

A couple of questions are still open though...
1. Reflections. I know high end receivers from pioneer, jvc have dedicated circuits in their tuners to filter them out. But was wondering if there are any related tips regarding the antenna itself.
Dipole antenna's/ Yagi antennas etc., There are ways, not too practical on a car. I could google you some guides with mathematics etc., but it wont be very useful in a car scene. You have to live with it, but don't worry, inside the city the signal is pretty strong. Anyways check out J-Pole google for it, there are DIY J-Pole antennas possible, but they are a little unsuited to mobile platforms
Quote:
2. Polarization. does it matter? was wondering if that would call for any additional care to be taken in antenna orientation. Hope not.
I should hope not, most stations broadcast left or right circular polarized signals right. For city use, I doubt that it will matter. Different stations have different settings, so if you were living 200kms away and wanted to listen to a particular station, you can go ahead and design that perfect antenna, but then in a car, everything you will do will be useless as the orientation and placement of the vehicle will change things.
Quote:
That obviously means that reception will be worst in minimum gain position. I thought that it will be even worser than a short wire, no? For example, if you are driving in city outskirts, reception will be good if station happens to be right in front of you or back side. But it will be bad when the station is exactly on either left or right side.
You will have a wire running from HU to the antenna right? That will suffise + you will get some gain from the dipole antenna. Moreover in the city there are reflections etc., also. Even the very incorrectly designed 1 feet long dipole windshield antenna works, right, this will work much better.

You can read up this if you want to look at more research
A Circularly Polarized FM Antenna for the Attic
Antenna (radio - Wikipedia, the free encyclopedia)

I am pretty out of touch as far as nitty gritties are concerned.

Last edited by tsk1979 : 7th June 2007 at 15:04.
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