fm transmitter

i wish to build fm transmitter of range 88-108MHZ and 5V power. any suggestions for any VCO chip that can be used with pll cd4046

mns said:

i wish to build fm transmitter of range 88-108MHZ and 5V power. any suggestions for any VCO chip that can be used with pll cd4046

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The CD4046 has a max frequency of about only 800kHz when it has a 5V supply.
A high speed 74HC4046 has a max frequency of about only 8MHz when it has a 5V supply.
Their output frequency would need to be multiplied many times to reach 100MHz.

A high quality FM stereo Micromitter uses an IC that has a frequency synthesizer with a PLL and it uses a quartz crystal :
https://electronics-diy.com/schematics/BH1417_fm_transmitter.htm
https://electronics-diy.com/BH1417_PLL_Stereo_FM_Transmitter.php

thanks for the reply.
to begin from mono fm transmitter, pll chip was suggested for better performance. will discrete VCO be stable?
(couldn't get 74hc4046 in local market place.)

The CD4046 is a VCO and a PLL. Its frequency is much too low for an FM band transmitter.

won't it is possible to use pll as frequency synthesizer so that it works for VHF band?

You can use a low frequency VCO to make FM then multiply its frequency many times to reach the 100MHz FM broadcast band. A PLL is not required.

You can use a high frequency VCO and a high frequency counter then use a low frequency phase detector to make your own PLL.

You can use a high quality low cost FM stereo transmitter IC that uses a quartz crystal and a PLL frequency synthesizer.

While on the subject of fm transmitters...

...I am also trying to build a simple fm transmitter using the two transistor schematic from:

https://www.aaroncake.net/circuits/fmtrans2.gif

My question is in regards to the electret microphone here...if I used one of the three wire electret microphones that radio shack sells, how would the diagram change to allow for that third wire? Would I move the placement of the mic down to the junction below so that the white wire is heading towards C4, the ground heading upward and the red wire towards R6? And if this is indeed the case, do I need to add a resistor somewhere?

Thanks for taking the time to read this - any advice would be greatly appreciated!

-LeeMorgan

That horrible circuit has the antenna connected to its tuned circuit. Then when anything gets close to or moves away from its antenna the frequency changes.
It doesn't have a voltage regulator so its frequency also changes as the battery voltage runs down.
It doesn't have pre-emphasis (treble frequencies boost) like radio stations have so it will sound muffled on an FM radio because radios have treble frequencies cut (the opposite of the transmitter's boost).

3-wire electret mics have one wire for 0V, one wire for its positive voltage source and the 3rd wire as its output. Look at Electret Microphones in Google and see its datasheet to see if it needs a load resistor to 0V or to the positive voltage source.

mns said:

won't it is possible to use pll as frequency synthesizer so that it works for VHF band?

Click to expand...

Here is another example:
https://hem.passagen.se/communication/fm_500.html