How can I increase FM transmitter frequency ?

Hi my friends,

I found a way for making a FM transmitter from a website (here)

In this tutorial I can transmit between 88-108 mhz. So I want to transmit more higher frequencies such as 0.5-2 ghz. Is it possible to increase transmitted frequency ?

I searched some points that how to increase transmitter, and I have had some results. Even If I perform coil and capacitor (these mentioned in tutorial which I wrote above), I cannot reach 1 ghz. So could you please tell me how can I transmit high frequencies ?

AC couple a coil microphone into the Vtune port of this:

https://www.digikey.com/product-sea...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

use a poteniometer of 22K or so to also superimpose a DC voltage onto the Vtune port to tune the center frequency

I doubt your current transistor can handle 2 GHz- you need to find a new transistor. With 88-108 MHz, you can use any conventional FM receiver but now you need to make a new one too. You need to redesign the circuit.

c_mitra said:

I doubt your current transistor can handle 2 GHz- you need to find a new transistor. With 88-108 MHz, you can use any conventional FM receiver but now you need to make a new one too. You need to redesign the circuit.

Click to expand...

What if I find high frequency transistor, Is it the only component that need to change ? Coil inductance also important for get high frequencies. There is a coil inductance calculator (here). Then from the other calculator (here), I calculate the oscillator's frequency with values of coil inductance and capacitor.

biff44 said:

AC couple a coil microphone into the Vtune port of this:

https://www.digikey.com/product-sea...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

use a poteniometer of 22K or so to also superimpose a DC voltage onto the Vtune port to tune the center frequency

Click to expand...

Or as you said, I can use an oscillator component which have high frequency, and if I use a potentiometer with oscillator I can control frequency of transmitter. But I dont know where I have to put oscillator and which components I dont need in circuit that I share website above. I am sorry that where is Vtune, where I have to connect oscillator and which component I have to remove from circuit.

Best regards.

Also, the circuit has simple tank resonator which is not the most stable because of small variations in resistance and capacitance. The carrier will be subject to drift. At 100MHz, you can use a PLL to stabilize the carrier but the circuit complexity will naturally increase. At GHz frequencies you need to use other tools to stabilize the carrier.

c_mitra said:

Also, the circuit has simple tank resonator which is not the most stable because of small variations in resistance and capacitance. The carrier will be subject to drift. At 100MHz, you can use a PLL to stabilize the carrier but the circuit complexity will naturally increase. At GHz frequencies you need to use other tools to stabilize the carrier.

Click to expand...

You are right I looked some PLL circuits and be daunted So I think first I make the simple circuit and get frequencies as high as I can, then If it is not satisfy me I will rotate to PLL.

You need to study on Tank circuit of radio transmitter.the values of Inductor coil(L) and capacitors will give you variable Frequency band.
Also you can calculate frequency by designing tank circuit(Oscillator circuit). Basically in simple FM Transmitter there is LC oscillator is used. So you better get start from Designing of Simple FM 3W 88-108Mhz Frequency Transmitter.Good luck!!

I feel that some suggestions are missing the obvious intentions of the original poster.

He's asking about a single transistor "FM" transmitter operated at 0.5 to 2 GHz. As said you need a suitable microwave transistor, let's say with at least 5 GHz fT. The resonator L will be rather formed by a small single turn loop or a transmission line stub than a coil. It can be tuned by a small varicap or by varying the inductor geometry.

The circuit can be best soldered on a piece of metal sheet or a RF veroboard with continuous ground plane.

A 0.5-2GHz band oscillator is absolutely different than FM band oscillator and this circuit will never work at that band even the components are changed.

First..
0.5-2GHz VCO ( I presume that the modulation will be FM ) is almost impossible. The classical VCOs cover approximately 1 octave not more.
Second..
This wideband VCO will have very high Phase Noise and the modulation cannot be very efficient. At least, the modulation will be very noisy.
Third..
Implementation of this VCO will require different PCB/layout techniques, topology, components, design etc.
and finally
This 0.5-2GHz band is licensed and nobody can transmit anything between those frequencies except some amateur bands.( 470-870 MHz TV broadcasting,900MHz for GSM, etc. )

Ok ıt seems, I need to be more professional to understand exactly what you said. First I try to make an normal bandwidth FM transmitter, then try to increase it. I know it isn't legal to transmit high frequencies, but I will do it according to rules.

So I just wonder that Is frequency divider such as 74HC93 possible to use for increasing transmitted bandwidth ? I have a circuit about frequency meter and there is an freq. divider (74HC93 or 74LS93) using for increasing Arduino's crystall frequencies. For example if you use 74HC93, with 16mhz crystall you can measure max 64 mhz. Are these freq. divider parts also use for FM transmitter ?

Thanks for all replies, I have illuminated.

FvM said:

It can be tuned by a small varicap or by varying the inductor geometry.

Click to expand...

The key point is how to keep the modulation within the +/-10kHz limit? Even a small varicap will cause a large change in frequency. Reducing the voltage to the varicap will only add noise. Am I missing something?