FM transmitter

[cizzi]

If I built this fm transmitter on a solderless breadboard would it work?

FM Transmitter

Thanks for your opinions.

 

[blueroomelectronics]

How did you not understand the last thread you started on the same subject.

YOU CANNOT MAKE RF CIRCUITS ON A SOLDERLESS BREADBOARD.

PS Aaron Cake circuits are really hit & miss.

 

[mvs sarma]

If I built this fm transmitter on a solderless breadboard would it work?

FM Transmitter

Thanks for your opinions.

Cizzi,
Why another thread for the same subject opened by you. what issues you have for assembling the one We suggested (FM TX Mod4).Afterall a PCB can be made if you are interested.
please see the link below
for a possible layout

https://www.electro-tech-online.com/threads/big-problem-with-small-fm-transmitter.37347/#post292811

 

[cizzi]

How did you not understand the last thread you started on the same subject.

YOU CANNOT MAKE RF CIRCUITS ON A SOLDERLESS BREADBOARD.

PS Aaron Cake circuits are really hit & miss.

Why don't you kindly explain to me why I cannot build an RF circuit on a breadboard?

 

[cizzi]

Cizzi,
Why another thread for the same subject opened by you. what issues you have for assembling the one We suggested (FM TX Mod4).Afterall a PCB can be made if you are interested.
please see the link below
for a possible layout

https://www.electro-tech-online.com/threads/big-problem-with-small-fm-transmitter.37347/#post292811

I want something simple, that diagram seems to complicated for a beginner, why don't you compare it to the one I showed you. Thanks.

 

[RadioRon]

Why don't you kindly explain to me why I cannot build an RF circuit on a breadboard?

The reason begins with our old friend IxR=V. If you have studied the concept of reactance, you may recall that this is the ability of an inductor or capacitor to resist the flow of AC current. Each inductor or capacitor's ability to resist this AC current can be calculated easily with simple formulae. For example the reactance of a capacitor is stated as:

Xc=1/(2 x pi x f x C)

Where f is the frequency in Hz and C is the capacitance in Farads. Xc is our symbol for the reactance.

Now, if you look at your example transmitter circuit, you will notice that C2 and C5 are very small capacitances. C2 is only 5.6 pF while C5 is variable from 3pF to 18pF. These values are important as they determine the oscillation frequency of the transmitter. What would happen if you put the wrong value in for, say, C2? The transmitter might transmit, but not at the frequency you expect, and so you would not hear it on your FM receiver.

When you use a solderless breadboard, you inadvertantely add a hidden capacitor between every connection. This is because the way the solderless breadboard is built, it has rows of metal strips layed side by side. Because the strips are fairly large and they are laid in parallel, they have a lot of capacitance between them. I measured my solderless breadboards and I find that each row has 3.3pF of capacitance to the next row. Not only that, but from each row to each alternate (second one over) row has 1.7pF and to each second alternate there is 1.2pF. And so on it goes. When there are hidden capacitors in the structure of our board, we refer to them as parasitic capacitance. The solderless breadboard has a lot of parasitic capacitance.

How bad is 3.3pF? Plug that into the formula above and you will see that the reactance is 482 ohms. This means that at a frequency of 100 MHz, the approximate frequency of your transmitter, the most reactance you will ever see from one row to another is 482 ohms, which is quite low. So the RF signal leaks from one row to the other through this 482 ohm capacitor. This leakage from one row to another ruins the transmitter's function. It does this in various ways, and the best way to see how much damage this capacitance does is by adding a capacitor symbol on your schematic between every point where a wire lead plugs into the breadboard. You will see that you are adding many capacitors, in places where they do not belong. Like for example you are adding a capacitor between the collector and the base of Q1. This will really mess up your transmitter's oscillator and cause it to not work. The destruction goes on with every added capacitor.

So, to put it in one short phrase, the solderless breadboard cannot be used for an RF circuit at 100MHz because it adds way too much parasitic capacitance between all of its connections, and these parasitic capacitors ruin the operation of your circuit.


PS: for those interested in this subject, I find that there is also an awful lot of capacitance from each row to the two buses at the top and bottom of the board. For example, from one row to the nearest bus, I measure 1.3 to 1.6 pF. This is even though they are not parallel to each other. From one row to the second nearest bus, there is also 1.3 pF.

 

[Techie7]

Why don't you kindly explain to me why I cannot build an RF circuit on a breadboard?

Cizzi,
A VHF circuit's frequency depends on the coil and cap. The cap value will be something in pf. The parasitic capacitance of breadboard will affect the whole operation. Because a breadboard has sockets made of plates and a dielectric in between rows(plastic maybe). It means that a breadboard has its own capacitance between its rows. That will affect the VHF operation. Got it? So when u try your circut on breadboard and when make to a pcb there's no guarantee that it will operate.better make ur working circuit on a pcb itserlf.

 

[mvs sarma]

I want something simple, that diagram seems to complicated for a beginner, why don't you compare it to the one I showed you. Thanks.

i feel, you should not confuse with a little of voltage regulation and a driver output stage. breakup the schematic into 4 parts and then while making you look at section by section.
1.voltage regulator(this part isused for the Mic and Osc-Mod section,
2.Mic pre amp with pre emphasis
3.FM oscmod.
4.Final amplifier.

Once you understand the schematic, perhaps you can make it and once made , you get best of its performance.
Many a time, people start with mini projects and once fail, they get discouraged. one person got lot of problems with just voltage regulator using 7805. In practice, only failures teach a person, even if it is your own design.
As you started with an RF circuit, you may not perhaps feel it complicated.

Thus i feel you take little time, understand and slowly build it following assembly practices. and without dry joints, component reversals, reverse supply voltages etc.

Finally you should have self confidence of course. Best appears that you wait for the next semester, as by then you would feel more confident.

 

[cizzi]

thanks for the detailed answers guys!

 

[bandulasat]

Can any one provide me a circuit diagram with lay out of a TV transmitter ( AV Tx.)which can radiate the signal to about 3 to 5 Kilo meters distance. It is great that if i can get the coil details and PCB pattern also. My e-mail address is bandulasat@hotmail.com
Thank you.

Bandula.

 

[bandulasat]

TV Transmitter Circuit

Hi '
Can anyone provide me a circuit for a TV Transmitter ( AV Tx. ) which can radiate the signals to a distance of about 3 - 5 Kilo meters. It is great if i can have the ciol details, PCB pattern and lay-out also.
Thank you
Bandula.

 

[Mikebits]

Hi '
Can anyone provide me a circuit for a TV Transmitter ( AV Tx. ) which can radiate the signals to a distance of about 3 - 5 Kilo meters. It is great if i can have the ciol details, PCB pattern and lay-out also.
Thank you
Bandula.

Oh brother, perhaps we should forward these post to Ladyt11...