One question about antenna sizes for fm transmitter

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ok guys thanks for the info so now i want to know if anyone knows of some simple fm transmitters with pre emphasis so they wont change frequency everytime i come near it?
 
oh and lastly my stupid fm transmitter picks up other stations when i tune it. so when i start tuning what used to be white noise on the radio urns into some station and its super hard to tune it to what i want that way. so plz provide a good schematic for a transmitter that wont have these problems
 
polishdude, just buy a short range RF transmitter... You obviously have no interests in electronics or RF design as an actual personal interest aside from your goal of causing your ipod to broadast to an FM receiver, which you can achieve with VERY cheap consumer hardware. Several links and references have already been provided for you, use them. A schematic which includes enough overall components to meet your requirements that could be made with discrete components would cost MORE than simply buying the appropriate device in the first place.
 
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Nigel/Ke5 could you provide links to how a base loaded whip changes the radiation pattern and feed impedance of an antenna? I've seen some refrence to this in a book I just read which explains how to pull short or long antennas into another band, I guess it affects bandwidth as well, but I'd like to read more.
 
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actually you are completely wrong. I am very interested in electronics and I am not doing this just to broadcast my ipod. I also want to learn and build my own. so please dont make assumptions like that
 
just searched google and in about 20 seconds found this schematic.

as the title on the website shows its perfect for your needs

**broken link removed**
 
It is your cheap radio that is overloaded by the nearby transmitter which causes it to pickup interfering stations.
My cheap Sony Walkman radio and my cheap clock radios get overloaded by my FM transmitter. My good quality hi-fi FM tuner and my good quality car radio do not get overloaded.
 
The 1W RF amplifier is made to boost the attenuated output of a good quality FM stereo transmitter, not the simple and cheap single-transistor mono garbage one.
 
Then you're going about it the wrong way polish.

Let me ask you this from a different perspective.
You're interested in automobiles, what's the first thing you do, go out and try to build an engine from schematics or understand all the details about how each portion of the engine works? You're trying to build an end product knowing nothing about how each of the components work. You need to start at a more fundamental level, you need to learn the basic math behind what's going on and the more advanced math if you can manage it.

If you have a love of movement you can't build a 500HP engine befor you learn how to ride a bicycle... Enough analogies for you?
 

I suggest you get ahold of EZNEC, which is a great antenna modelling program where you can experiment til your hearts desire.

And the link I gave you earlier will also discuss antenna loading and its effects, but a real good place to look is in a real paper book, which the ARRL has many, many great publications on various antenna theory as well as full version EZNEC software.
 
Nigel Goodwin said:
5/8th whips use loading coils at the bottom to match them, so it's obvious if it's a 5/8 whip. They were very commonly used by radio amateurs on cars for 145MHz.
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Mr. Nigel,

While loaded 5/8 whips for 2 meters are not uncommon to be certain, it is snake oil to purchase such an antenna and few amateurs would waste their time homebrewing one since a 5/8 wave antenna on 2 meters is just over a meter long. What a waste of power.

It is much, much more common to see loaded designs for HF frequencies or CB radio (11 meters)
 

Yes, loading an antenna does effect bandwidth, as does the thickness of your antenna element.

But loading an antenna is not considered desirable, just a sometimes necessary consequence of mobile antenna construction.

You will have loss in the form of heat at the coil, and you will have an undesirable radiation pattern (as compared to an ideal radiator).

A loaded 5/8 wave vertical antenna may, however, outperform a 1/4 wave vertical if the design is good and the ground plane is adequate...for the angle of radiation reasons I mentioned earlier. You will have loss in the form of irregular patterns caused by the coil, but there will still be enough desirable low angle radiation to make it a superior choice over a 1/4 wave.
 
Sceadwian said:
Nigel/Ke5 could you provide links to how a base loaded whip changes the radiation pattern and feed impedance of an antenna?
Click to expand...

The base loading doesn't affect the radiation pattern, it simply corrects the impedance. The radiation pattern is down to the length of the aerial.

If I can find my VHF/UHF Manual, I'll see what it says about 5/8 whips.
 

Not snake oil at all, a 5/8 whip on a car considerably out perfroms a 1/4 wave one - and they weren't just 'uncommon' they were EXTREMELY common back in my radio ham days. Personally I never used one, but I did work mobile on a motorbike with a 1/4 wave whip

5/8 would be a bit big on a motorbike.

Frequency and size don't matter, a 5/8 (or any other size) will perform equally at whatever frequency it's built for. Aerial design and testing is normally done at mush higher frequencies because it's easier to measure, and can even be done indoors.

It is much, much more common to see loaded designs for HF frequencies or CB radio (11 meters)
Click to expand...

Yes, due to the fact it's difficult to build or site full size aerials, but a 5/8's whip is LARGER than a normal full size aerial anyway, and you wouldn't normally use them at HF.
 
I think you misunderstood me. I don't disagree with you that 5/8 verticals are common, extremely common, on 2 meters. I can look out my window and my own vehicle and attest to that, as I have one. However, it is homebrew and isn't loaded.

Most of your VHF/UHF combo antennas are 5/8 wavelength on 70 cm (1/4 on 2 meters), and aren't loaded, or have only a small zig-zag or three or four turn small spiral in the middle (technically a loading coil yes but its purpose is to help with bandwidth and tuning on a 2 band design)

My point was that most people who homebrew are going to go with a non loaded design because the coil consumes power...and I disagree about the radiation pattern. When a coil is introduced it produces higher angle lobes in the pattern. A non-loaded 5/8 vertical is superior to a loaded one....(the difference is negligable in all honesty, as it might buy you just a few extra miles going down the highway...but you know us hams, always trying to make our signals better!)

You said "Frequency and size don't matter, a 5/8 (or any other size) will perform equally at whatever frequency it's built for. Aerial design and testing is normally done at mush higher frequencies because it's easier to measure, and can even be done indoors"

If you are saying a 5/8 will perform equally to a 1/4 wave for the frequency it is built for...I apologize for being critical but obviously you never used a field strength meter or modeled an antenna on computer software. A 5/8 wave has better angle of radiation.
 
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I'm talking about single band 5/8 whips, normally used for 2 meters, the small size of 70cm aerials means better ones are commonly used (co-linears etc.).


So how do you match it?, the loading coil provides the matching to the transmitter/receiver.


No, I fully agree a 5/8 out performs a 1/4 wave.

You seemed to be suggesting a 5/8 whip at 145MHz wasn't as good as a 5/8 whip at HF frequencies - where I don't think a 5/8 would be used anyway?.
 
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