Improving 100mW FM Transmitter Design

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    Inductor Receiver
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Discussion Overview

The discussion revolves around the design and functionality of a 100mW FM transmitter, particularly focusing on the role of inductors and capacitors in radio receivers, tuning circuits, and methods to increase transmission range. Participants explore theoretical concepts as well as practical challenges related to radio frequency transmission.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants explain that inductors in receivers are part of a tank circuit that selects the desired frequency, often in conjunction with a variable capacitor.
  • There is a suggestion that increasing the input voltage, adding an amplifier, and adjusting antenna length could enhance the transmission range of the FM transmitter.
  • One participant raises concerns about regulatory limits on transmission power and the potential for interference with neighbors.
  • A participant describes the resonant frequency of an LC tank circuit and how it resonates only at that frequency due to the cancellation of reactances.
  • Another participant questions whether the issue with the limited range might be related to the receiver or antenna design rather than the transmitter itself.
  • There are multiple inquiries about the compatibility of the transmitter's frequency with the receiving capabilities of modern cell phones.
  • Some participants express confusion regarding the use of cell phones to receive signals at the specified frequencies.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of the current transmitter design and the potential solutions for increasing range. There is no consensus on the cause of the limited range or the compatibility of the transmitter with the receiving devices.

Contextual Notes

Participants note the importance of considering regulatory limits on transmission power and the design of antennas, which may affect the performance of the transmitter. There is also a mention of the challenges in achieving desired results at higher frequencies due to component behavior.

Who May Find This Useful

This discussion may be useful for hobbyists and engineers interested in radio frequency design, particularly those working with FM transmitters and receivers, as well as those exploring the theoretical aspects of LC circuits.

  • #31
One more comment. Was your transmitter bought or did you make it? It may just not be working optimally. You can make a vast difference to equipment, working at those frequencies by bending and tweaking coils and leads. You have the problem of not much available test gear, of course, which makes things doubly difficult.
 
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  • #32
sophiecentaur said:
One more comment. Was your transmitter bought or did you make it? It may just not be working optimally. You can make a vast difference to equipment, working at those frequencies by bending and tweaking coils and leads. You have the problem of not much available test gear, of course, which makes things doubly difficult.

I made it
This is the circuit diagram
What should i do please suggest some tips
 
  • #33
Transmitter
 
  • #34
Is unlicensed fm transmission still limited to 100mW? I think it is.

The schmatic has been posted already in post 8.

I'd try making C2 a variable cap and see if it helps the antenna match.
What are you using for a transmit antenna?

Look at http://www.circuitstoday.com/2-km-fm-transmitter for a better design.
 
  • #35
meBigGuy said:
Is unlicensed fm transmission still limited to 100mW? I think it is.

The schmatic has been posted already in post 8.

I'd try making C2 a variable cap and see if it helps the antenna match.
What are you using for a transmit antenna?

Look at http://www.circuitstoday.com/2-km-fm-transmitter for a better design.

I'm using a wire as antenna
 
  • #36
meBigGuy said:
Is unlicensed fm transmission still limited to 100mW? I think it is.

The schmatic has been posted already in post 8.

I'd try making C2 a variable cap and see if it helps the antenna match.
What are you using for a transmit antenna?

Look at http://www.circuitstoday.com/2-km-fm-transmitter for a better design.

The problem with building circuits at 100MHz is that the way it's laid out is so important. Use of a ground plane and proper decoupling where it counts can make all the difference.
If neeraj kaira wants something that will just 'work for him' then he may not want to develop too much expertise as a result of 2nd and 3rd versions for laying out that circuit. That other schematic you provided is potentially better and more stable but it still needs to be soldered together with short lead lengths, disc ceramics in the right places, physically, etc.. The least he would need, I should say, would be a construction leaflet with a picture of a working model to work to - in addition to the schematic. You can often buy kits with a PCB which you just have to populate. That's the ideal way to get results, for starters.
 

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