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Finished my first project :D(need some help on some fine tuning)

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(and don't tell me that its because i am using a breadboard because it worked more then once)[/QUOTE]
can't read well?
also i won't be able to move it to a pcb\pref board for some time
 
maor said:
it works great even so there is some noise and im no sure about the range of the transmitter.
So, it does not work all that great then, does it?

maor said:
Also when i removed the coil from the circuit there was no difrence in any way from with the coil and W/O the coil.
In which case, the circuit was not working as its designer intended.

maor said:
I think the noise is being caused by the face im using just random(with the correct values) caps the circuit did say use 1% low noise caps but i don't i have any of those so i just used any kind of cap i had.
So, you did not use the correct components.

maor said:
I think i didn't do the coil right...
I guess not.

maor said:
Is the coils purpose to like lower the noise in the transmittion?
No, it is not.
The coil, in conjunction with its associated capacitors makes a tuned circuit so that the oscillator can run at the correct frequency.

Oh, by the way, plug in breadboards dont work very well at high frequencies, I speak from experience.
Many years ago, I tried to lash up an oscillator running on 20Mhz and used a breadboard, as much as I tried it did not work.
Taking the same components and soldering them to a piece of plain circut board, and gues what, the oscillator started as soon as I applied power, and near enough on the correct frequency.

So, maybe you did not understand when experienced guys try to give you advice.
Audio and Nigel are not little kiddies who have just fallen off the Xmas tree, listen to what they say and learn.

JimB
 
In short, just because it 'sort of worked' when you built it on a bread board, it doesn't mean Nigel and audioguru are talking rubbish when they say don't build it on a bread board. Things might work when they're not supposed to work, this normally means that they won't work nearly as well as they're supposes to and may also exhibit temperamental behaviour.
 
I built an FM transmitter on perf board using the correct parts about 44 years ago and it worked pretty well. It could be tuned over most of the FM band with its tuning capacitor.

I made a better FM transmitter on stripboard using the correct parts two years ago and it works perfectly.
 
You may be able to get the circuit to operate on a breadboard but that's the only place it'd work, and even then it's operation wouldn't be reliable, simple tension on a wire would cause a variable capacitance as well as any oxides on the contacts. Once moved to perfboard/PCB the circuit would cease to function or operate in a different manner because the stray capacitances are gone. If you don't believe Nigel, blueroom, hero, audioguru, or me that it's a bad idea, look at the Wikipedia entry which states that frequencies above 10mhz aren't usually used. There are some exception being that I've seen many people use breadboards for 16 or 20mhz crystal oscillator setups but if moved to perfboard or PCB load capacitors have to be changed to compensate.

Just to give you an idea, at 10mhz assuming the worst case 20pf's capacitance per row that's real close to being the same as putting a 1k resistor between every pin of every component on the board of a board without the stray capacitance. Increase that to 100mhz, that's closer to 100 ohms
 
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JimB said:
Oh, by the way, plug in breadboards dont work very well at high frequencies, I speak from experience.
Many years ago, I tried to lash up an oscillator running on 20Mhz and used a breadboard, as much as I tried it did not work.
Taking the same components and soldering them to a piece of plain circut board, and gues what, the oscillator started as soon as I applied power, and near enough on the correct frequency.

So, maybe you did not understand when experienced guys try to give you advice.
Audio and Nigel are not little kiddies who have just fallen off the Xmas tree, listen to what they say and learn.

JimB
was it so hard to explain it to me like that?
now i understand why it can't done on a bread board...
one more question do you think it will work on AM freq?
EDIT:
forgot another question that i am not sure you will mange to answer
if the tuning cap generates the freq(right?) as in doing a chrage and discharge 88-108 million times a second how come when the capacitance is lower the freq is lower aswell? shouldn't it be the other way around?
 
maor said:
was it so hard to explain it to me like that?
now i understand why it can't done on a bread board...
one more question do you think it will work on AM freq?
EDIT:
forgot another question that i am not sure you will mange to answer
if the tuning cap generates the freq(right?) as in doing a chrage and discharge 88-108 million times a second how come when the capacitance is lower the freq is lower aswell? shouldn't it be the other way around?

No, that's the correct way, but it's not a question of 'charging and discharging', it's an LC resonant circuit.

Frequency = 1 / ( 2 x PI x Squareroot(L x C) )

I also wouldn't advice using a breadboard for anything higher than audio!.
 
Nigel Goodwin said:
No, that's the correct way, but it's not a question of 'charging and discharging', it's an LC resonant circuit.

Frequency = 1 / ( 2 x PI x Squareroot(L x C) )

I also wouldn't advice using a breadboard for anything higher than audio!.
btw nigel when someone asks you the question about why you can't make fm circuit on a bread board don't just give them the facts tell them why aswell
 
maor said:
btw nigel when someone asks you the question about why you can't make fm circuit on a bread board don't just give them the facts tell them why aswell

You could also try searching the forum for the other hundreds of identical threads! :p
 
maor said:
do you think it will work on AM freq?
If by "AM Frequencies" you mean 500 to 1600kHz, I will stick my neck out and say yes it will, you will probably get away with it.
The stray capacitance between the tracks and the stray inductance of the tracks themselves has nowhere near the effect at MF that it does at VHF.
However, if I were trying to evaluate a circuit at any radio frequency, I would just use some form of "Ugly Construction" on a sheet of plain copper clad circuit board.


maor said:
forgot another question that i am not sure you will mange to answer
mange? a skin disease found in dogs and cats?:D


maor said:
if the tuning cap generates the freq(right?) as in doing a chrage and discharge 88-108 million times a second how come when the capacitance is lower the freq is lower aswell? shouldn't it be the other way around?
The tuning capacitor and the coil determine the frequency.
If the value of either (or both) goes down, the frequency goes up

JimB
 
Just a little side issue, which as a radio person, really pulls my chain...

AM frequencies and FM frequencies.

AM = Amplitude Modulation
FM = Frequency Modulation

The carrier frequency has nothing to do with it, other than that commercial broadcast stations use AM between 500 and 1600khz and FM between 88 and 108Mhz.

It is quite possible to frequency modulate a low frequency carrier and amplitude modulate a VHF carrier.

<End Of Rant>

JimB
 
=maor said:
btw nigel when someone asks you the question about why you can't make fm circuit on a bread board don't just give them the facts tell them why aswell
In the third reply to this thread, Nigel confirmed audioguru's analysis and explanation (in the immediately previous post to Nigel's) of the bread board problem. To reiterate what someone had just explained to you would have been pointless. I would've thought it to be comforting to have both one member give you the details, and another member second the motion, as it were.

You know, you could just buy a book or pay for a course in the subject, as most people do. If you get something for free, you can't expect to return it and file a complaint with customer service.
 
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When I get something for free, I return it and get its full price back.

If the price scanner in most stores at the cashier is wrong then you get the item for free. I get lots of things for free.

I can buy something on sale at one store and take it back for a full price refund at a different store. The customer is always right (so the store doesn't lose a customer) even if there is no receipt.

I haven't done it but I have seen a person walk into a store, select merchandise then get their money back. They didn't even buy anything.
 
This circuit puts out both AM and FM.

At MF the frequency shift due to the change in the transistor's capacitance with be negligible and any FM produced will only effectively enhance the modulation index as it slides to either side of the carrier frequency slightly.
 
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