Help for a school Physic Projet ''Bulding a FM transmitter ''

[Vince147]

Hi, i am a student at college in pure science and for my last session, i am doing a physic project who consist in building a FM transmitter and a FM receiver. I have chose one of the model in this website ''simple fm transmitter '' made by Izhar  Fareed (http://www.electronics-lab.com/projects/rf/012/index.html) and i have some questions.

I want to change the microphone for a jack connection relied to an ipod. My objective is to play a song and heard it thru the speaker of the receiver. I am now at the first part of the project, witch is building the transmitter without the ipod. I had to change some value inside the circuit because the school didn't have the exact components.

Result, the transmitter works but the frequency i reach was around 45MHz instead of 100MHz.  I have tested to bring up the voltage from the source to observe witch effect that will create to the frequency in case of buying some part for nothing. Absolutely nothing, the only effect that made was raise up the amplitude of the wave form. Also, reduce the value of the resistance had the same effect and raise up is the opposite. Removing some condenser was nothing decisive at that moment.

I decided to go buy all the exact components who figure in the transmitter list description.

So now, i have all the exact components. I can believe that will work better then with the replacement i have to deal with at school.

So,to return to my main question, what i need to do if i want to put a jack connection link to my ipod? What component  i need to change or add to respect that high variation of signal?

Thx everyone. If you have some idea or commentary about the transmitter or the receiver, i will be happy to heard it. I have not choose  the type of receiver yet because i need to fix my transmitter before doing anything else.
I have some difficulty on that project because i don't have some specialize resource at my school. That would be great if someone can help . I've prefer to explains all  the experiment i did before having any wrong conclusion.


Vince147

 

[audioguru2]

The radio frequency of the FM transmitter is determined by the LC tuned circuit. But the text of this project is wrong, the coil is about 0.1uH, not 1uH.

The text does not say how to make the coil. It is about 6 to 8 turns of enamelled wire with an inside dimension of 3mm. I attach a photo of a coil with only 4 turns (not enough turns) and the turns are spaced too far apart.

The first transistor amplifies the very weak signal from a microphone and should be removed and replaced with a 10k volume control or trimmer resistor. I attach the modified schematic.

The circuit must be built very compactly on perf board, stripboard or a pcb. It will not work if it is built on a breadboard.

Its antenna is connected directly to the tuned circuit so the radio frequency will change if something moves toward or away from the circuit or the antenna.
The frequency will also change as the battery voltage runs down.
All FM radio stations boost treble audio frequencies and all FM radios cut the boosted high frequencies back down to normal (and cut hiss) so this transmitter will sound muffled on an FM radio.

Where will you find all the special parts to make an FM radio?

View attachment 41580

View attachment 41581

 

[Vince147]

thx very much

 

[Vince147]

there  is a electronic store at Ottawa near by my place : Gervais Electronic : http://www.gervaiselectronics.ca/

 

[Vince147]

When you said a dimension a 3mm, are you talking about the diameter of the wire or the inside diameter of the spire?

 

[audioguru2]

When you said a dimension a 3mm, are you talking about the diameter of the wire or the inside diameter of the spire?

3mm is the inside diameter of the coil. Wrap enamelled wire around a 3mm drill bit, slide the coil off  then scrape off the enamel at each end so you can solder to the wire.
I use thick wire that has 1mm diameter so it is strong enough not to get bent out of shape that changes its inductance that changes the radio frequency.

 

[Vince147]

alright, i will try that tomorow.
I have another question if you mind.

You said already that the signal i made will the emitter is not clear and i did experience that will the last inductance (the one with the original emitter plan).

Do you know how i can improve the quality of the [glow=red,2,300]signal[/glow]? You have give me some info about the inductance and i will work with that tomorow but, if the signal is not clear enough with the new inductance, do you know how i can increase the quality of the [glow=red,2,300]signal[/glow]?

Thx
Ps : When i say the signal[glow=red,2,300][/glow], i mean that one i heard on the FM receiver witch is my song played on the ipod.

 

[audioguru2]

Do you know how i can improve the quality of the ? You have give me some info about the inductance and i will work with that tomorow but, if the signal is not clear enough with the new inductance, do you know how i can increase the quality of the signal?

Ps : When i say the signal, i mean that one i heard on the FM receiver witch is my song played on the ipod.

Please explain what is the problem with the quality. Does it have hiss? Does it have hum? Is it distorted? Is it too loud? Is it too soft? Does it sound muffled with no high audio frequencies?
Does the radio signal appear at many spots on the dial of the radio?

 

[Vince147]

We did hear the signal around 92-93MHz the first time and the next week after, we did receive it around 88MHz. We didn't not change anythink in our system. There is just two think different from your plan :

1) We have to put a 12.50V batterie to opperate the system in the FM band.

2) We had try to build the inductance with your specification but that ain't work. The instrument we use to read the inductance have some difficulty to read a small value like 0.1uH. So, we still have switch the 1uH for the 0.1mH (6turns and another one of 8turns) but it got worse. We can heard the signal with the 1uH but not with the 0.1mH. We had search the entire FM band and we have raise/down the source voltage and nothing happen. So we still work with the 1uH. Our electronic seller dont have the 0.1mH in stock.

To respond to your post, we can set the radio to a frequency and heard the music from the ipod. If we unplug the antenna, we stop the signal, so we know that is our emitter signal. For the signal heard ( the sound), its seem to have hum ,it too loud and the high audio frequencies are barely absent.

Still, when we know what song is played on the ipod and we hear the signal, we are able to recognize the song with the ''bass'' and some other sound from it. (Daft Punk : One More Time)

 

[Vince147]

++++++ The signal can be hear in +/- 0.3MHz channel around the selected frequency.
Example :    we select 90MHz 

  we heard it from 89.7 to 90.3MHz

 

[audioguru2]

If the volume from the music source is turned up too high then the FM transmitter swings its frequency too wide and causes severe distortion in an FM radio. The maximum deviation from an FM radio station a full volume is +/- 0.075MHz.
Turn down the volume so the transmitted signal heard on the FM radio is not louder than FM radio stations.

Mains hum will be picked up if ordinary wires connect the music source to the transmitter. Shielded audio cable must be used to block hum pickup. Or maybe your power supply has hum.

 

[Hero999]

How are you powering the transmitter?

 

[Vince147]

I use a 12,5V battery. That was the only value we can select to get inside the FM band. The battery is one of the model the technician use for the Electricity class in pure sciences.

Also i have another question for you. Do you know another circuit plan for a FM receiver?
I tryed to find some but all of them was too much hard to inderstand with my college knowledge.

Thx Again for your help.

 

[Hero999]

Audioguru designed a better transmitter while ago. Here's a link to the project.
http://www.silicontronics.com/index.php?action=ezportal;sa=page;p=15

 

[Vince147]

Hi, im doing a physic projet for school and i need a receiver plan. The one i find on the internet was too hard to understand for my college knowledge. Thx

 

[audioguru2]

A high quality and very sensitive FM receiver is very complicated with many parts that are almost impossible to buy unless you buy a high quality receiver and take it apart to re-use its parts.

An extremely poor quality FM radio costs $1.00 at The dollar Store. It uses a Chinese copy of an obsolete European toy radio IC.

I have a Sony Walkman FM stereo portable radio. Its performance is fairly poor but it picks up strong local stations well. Its IC is not made anymore ands a similar European radio IC is also not made anymore.

 

[Hero999]

Hi, im doing a physic projet for school and i need a receiver plan. The one i find on the internet was too hard to understand for my college knowledge.

Then you need to learn more.
Why not post a link to the schematic you've found so we can explain it to you.

 

[paulinehepburnzpe37]

Hi, i am a student at college in pure science and for my last session, i am doing a physic project who consist in building a FM transmitter and a FM receiver. I have chose one of the model in this website ''simple fm transmitter '' made by Izhar  Fareed (http://www.electronics-lab.com/projects/rf/012/index.html) and i have some questions.

I want to change the microphone for a jack connection relied to an ipod. My objective is to play a song and heard it thru the speaker of the receiver. I am now at the first part of the project, witch is building the transmitter without the ipod. I had to change some value inside the circuit because the school didn't have the exact components.

Result, the transmitter works but the frequency i reach was around 45MHz instead of 100MHz.  I have tested to bring up the voltage from the source to observe witch effect that will create to the frequency in case of buying some part for nothing. Absolutely nothing, the only effect that made was raise up the amplitude of the wave form. Also, reduce the value of the resistance had the same effect and raise up is the opposite. Removing some condenser was nothing decisive at that moment.

I decided to go buy all the exact components who figure in the transmitter list description.
A project to build an FM transmitter sounds interesting and educational. I have never had such projects. Then I thought it was boring. Now I look at the assignments that are given in schools and colleges. At least they look interesting.
So now, i have all the exact components. I can believe that will work better then with the replacement i have to deal with at school.

So,to return to my main question, what i need to do if i want to put a jack connection link to my ipod? What component  i need to change or add to respect that high variation of signal?

A project to build an FM transmitter sounds interesting and educational. I have never had such projects. In general, I often turned to top writers and used 

[SIZE=10pt]https://edubirdie.com/top-writers[/SIZE] for this. I didn't like writing anything. Then I thought it was boring. Now I look at the assignments that are given in schools and colleges. At least they look interesting.
Thx everyone. If you have some idea or commentary about the transmitter or the receiver, i will be happy to heard it. I have not choose  the type of receiver yet because i need to fix my transmitter before doing anything else.
I have some difficulty on that project because i don't have some specialize resource at my school. That would be great if someone can help . I've prefer to explains all  the experiment i did before having any wrong conclusion.


Vince147

need to look into your question.