need help on my final stage of AM transmitter

[Weis Guy]

am transmitter

I am almost done in my AM transmitter using XR2206. The output produces a good modulation. The output can tensmit up to 1 to 2 mtrs in its field strength. The only problem i've got is my AMPLIFIER (RF Amplifier) stage and in my antenna. Can anyone share any ideas on how to create a RF Amplifier usinf CLASS C amplifier and please help me also for my antenna.

 

[House_Cat]

The first thing I need to mention is your choice of Class 'C' for the PA. Class 'C' amplification is non-linear therefore unsuitable for AM. Your modulated signal would probably be completely uninteligible. For AM RF amplification, you are restricted to Class 'A', or 'AB' for best performance. Class 'B' could be used; however, crossover distortion is difficult to prevent.

Class 'A' would be the easiest to implement, but the least efficient. It could be built single ended with a relatively simple circuit.

Class 'AB' requires a push-pull output stage. It would be more efficient than the Class 'A', but more complicated.

To comment on the antenna, you need to tell us what center frequency you are planning to transmit/receive. You also meed to tell us what space restrictions you have - i.e. is this to be handheld, base mounted, etc.

 

[toonafishy]

House_Cat is right about the amplifier. Take his advice.

Is this a school project? For the antenna, I once made one from wire mounted on a board. The wire was wrapped just like you would see a spiral inductor on an IC. It was for a school project and I ended up with the longest transmit distance. Something similar to this:

h**p://www.radioera.com/early-antennas.htm

 

[biff44]

I do not concur! If he is using pulse amplitude digital modulation at a farily low data rate, class C amplificaton is perfectly fine, and in fact is preferred for efficiency.

If he was using linear analog, say to transmit analog voice, then class C should not be used.

 

[Weis Guy]

It is just for a hobby,i've got a transmission without using an Amplifier but there is a slight problem, when i put a direct antenna to my output there is a radiation of signal but there is noise but when i touch the antenna the some noise are eliminated..I tried using longer antenna and some errors in radiation is corrected..maybe i will put some amplifier in my output stage so that it match to certain size of my antenna..Can you give me concept circuit of the amplifier stage and equations?ü

 

[biff44]

Did you read the responses? We need to know what type of AM modulation you are using.

 

[Weis Guy]

DSBSC

 

[biff44]

Then forget what I said, you need a linear amp.

 

[Weis Guy]

Got any ideas on the coupling circuit for the antenna?I'm having problem with it..Im testing my transmitter @ 1MHz..I need a concept or a circuit.

 

[Weis Guy]

still got problem with the output..by the its not DSBSC but its DSBFC..I have 2Vpp on my output..I need to put an amplifier on the output to increase the range of the transmitter..What should I do..Please discuss on what should I add after the output..Also please discuss the antenna part..What should it be?