Low level AM Transmitter Circuit and little description.

[Eshal]

Finally, here is my low level AM transmitter,



Both of you experts, kindly review throughly this circuit, values of components, value of power supply, everything, because I am going to use this as my project.

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Transistor,
For modulator section: BC548
For oscillator section: 2N3904
For RF amplifier : BF459

Are these right transistors?

 

[goldsmith]

Finally, here is my low level AM transmitter,



Both of you experts, kindly review throughly this circuit, values of components, value of power supply, everything, because I am going to use this as my project.

- - - Updated - - -

Transistor,
For modulator section: BC548
For oscillator section: 2N3904
For RF amplifier : BF459

Are these right transistors?

You values seems correct . an advise : first section that you should build and be sure about it's performance , is oscillator section , independently . then you can easily add other sections . by the way , do you have an oscilloscope or perhaps do you have access to one of them ? it is pretty important to see the result with oscilloscope .

 

[Eshal]

an advise : first section that you should build and be sure about it's performance , is oscillator section , independently

First section : Oscillator
Second section : Modulator
Third section : RF amplifier
Is that order should be?

by the way , do you have an oscilloscope or perhaps do you have access to one of them ? it is pretty important to see the result with oscilloscope .

No bro, I don't have :-(
But I know how to use simulators

 

[goldsmith]

First section : Oscillator
Second section : Modulator
Third section : RF amplifier
Is that order should be?

Yes

No bro, I don't have
But I know how to use simulators

How about your university ? can't you test your circuit there ?

 

[Eshal]

Didn't Shayaan tell you that our department teachers don't allow any student to use instruments out of practical days?
They don't allow us to use them, so I can't, and it is really bad... :-(

 

[goldsmith]

Didn't Shayaan tell you that our department teachers don't allow any student to use instruments out of practical days?
They don't allow us to use them, so I can't, and it is really bad...

No shayaan didn't tell it . but i think it is very bad . but don't worry , a simple way to test is available ! using a capacitor and then a rectifier and filter and then a DC voltmeter ! do you have voltmeter ?

 

[Eshal]

Yes I have in cupboard. What I have to do?

But bro, I don't have components yet...

 

[goldsmith]

But bro, I don't have components yet...

Oh yes i see ! for a little time i confused with myself ! because when i started electronics i had gang of electronics components in my home !

Yes I have in cupboard. What I have to do?

It is my suggestion to each people that haven't access to the oscilloscope ! see below , please :

DIodes can be 1n4148 and out put capacitor can be a simple 470nf or a bit lower and resistor in series with input can be 100 ohms and out put resistance can be around 100k . do you know how this circuit can do it's best instead of oscilloscope ?

 

[Eshal]

So this small circuit work as an oscilloscope?

Really???????

 

[goldsmith]

Ha ha ! yes ! for your purpose yes . when i was a little boy i had not enough money to buy an oscilloscope , and i tried to do my aims without problems . and after some times i could buy an oscilloscope !
If you put a volt meter in out put it will show you a value . it means your circuit oscillated . ( because that capacitor in input won't allow DC signal to go through . )

 

[Eshal]

Please bro, give me a clear and full diagram with component specification and with input output terminals.. please....

 

[goldsmith]

components of what ? transmitter or that oscilloscope trick ? if transmitter , there are many suggestions during this thread . didn't you see ?

 

[zsolt1]

good girl :wink:

you do not have to use the graetz bridge (or whatever its name is) for tests.... it vill only show efective value of voltage (or less at high frquency)... just use directly a radio reciver to se if works or not.
Ps : the modular construction is a good idea, if you don't like how a module works you can replace it later...

 

[goldsmith]

you do not have to use the graetz bridge (or whatever its name is) for tests.... it vill only show efective value of voltage (or less at high frquency)... just use directly a radio reciver to se if works or not.
Ps : the modular construction is a good idea, if you don't like how a module works you can replace it later...

Oh yes , i'm agree with Zsolt1 . if you use a radio receiver , thus at frequency of operation ( of that station ) without modulator stage you will hear nothing ! station will be calm and without voice and then if you open the battery from it's supply , it will stop oscillations and then you will hear some noises ( if your radio has not any shutting up circuit ) . why it didn't came into my mind ? ha ha ! :grin:

 

[Eshal]

Oh yes , i'm agree with Zsolt1 . if you use a radio receiver , thus at frequency of operation ( of that station ) without modulator stage you will hear nothing ! station will be calm and without voice and then if you open the battery from it's supply , it will stop oscillations and then you will hear some noises ( if your radio has not any shutting up circuit ) . why it didn't came into my mind ? ha ha !

I didn't understand this. Tell me in more convinient way. You said if I disconnect the supply coming from modulator to the oscillator, I will hear nothing.
And further you said if I open battery from it's supply, it will stop oscillations. How? If I allow supply to the oscillator section from modulator section then oscillator will generate frequency, how would it be stopped?

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you do not have to use the graetz bridge (or whatever its name is) for tests.

greatz bridge????

 

[zsolt1]

leo graetz - https://en.wikipedia.org/wiki/Diode_bridge
hehe , confused ?
Just do this : build the tx on 3.5 MHZ, apply a modulator signal, for the begining do not use microphone, use for example music from your pc .Take a radio reciver that has SW band, tune it somwhere around 3.5 MHz (it's scale may not be precise , but does not metter....), then tune the oscillator until you can hier your music on the radio . Redy :grin:
If you hier the music distorsioned, it is to much modulation , you reduce the amplitude of the modulator (the pc volume ) signal until you hire the music clearly . In oposite case if you hire the music weak, you increase modulator signals amplitude.
Ps: if you can't get radio which has SW band, use the one you have with MV band and search a frequency where you don't have any radio stations then tune your tx on that frequency with the above described method. Even if you accidentaly may transmit on some stations frequency, you will observe that imediatly since you are using a radio for tuning (you wil hier that radio station to)

 

[Eshal]

Oh I see. you and goldsmith are well educators. Your way of teaching is very easy, simple and inituitive. Thank you.

Just do this : build the tx on 3.5 MHZ,

Can you tell me what is tx??

 

[zsolt1]

tx - transmiter
rx - reciver

 

[Eshal]

Oh... So this is a code word for transmitter and receiver...

 

[goldsmith]

Hi again Zsolt1
As i promised here 2nd circuit coming ! a simple PWR meter ! if you use a voltmeter across the capacitor , you can know about out put power of your transmitter . ( i.e input will be across the 150 ohm resistors ) . this is kind of virtual load . these resistors should be high wattage . equal impedance will be around 50 ohms ( an antenna ) or you can set it for 75 ohms . power of resistors should be equal to the wattage of transmitter . but it is not a good idea for very high power transmitters !
( by the way did you see that simple radiation meter ? )


Best Wishes
Goldsmith