一款优秀的分立元件发射机电路(英文)

文章摘要： Frequency Modulation Pre-emphasisIf you wished to use audio directly from a PC or CD-Player, then you should add some form of pre-emphasis. If you are using a stereo encoder or FSK applications then you should NOT use pre-emphasis. Pre-emphasis increases treble a little so that when it is received

一款优秀的分立元件发射机电路(英文),标签：电路设计,http://www.88dzw.com

Frequency Modulation Pre-emphasis

If you wished to use audio directly from a PC or CD-Player, then you should add some form of pre-emphasis. If you are using a stereo encoder or FSK applications then you should NOT use pre-emphasis. Pre-emphasis increases treble a little so that when it is received and turned down again, added noise is also turned down. Select Cx(nf) to be 10x the number of Microseconds of pre-emphasis you want. If you wanted 50uS pre-emphasis then Cx = 50 x 10 nf = 500nf.

Possibilities

The resistor R1 may be removed from the circuit and the loop voltage from a synthesiser added to "Ctrl" on the circuit board. This will give the synthesiser a 10MHz tuning range, the preset capacitor determining the centre frequency. The loop frequency control voltage can be increased to about 20v but it should be maintained somewhere around 9v to get repeatable modulation characteristics.

The coil of the tuned circuit can be reduced and TR1/TR2 replaced for more suitable RF devices, then the TX can be increased to the 144MHz band and modulated with NBFM. In this situation one MUST use synthesiser control to stabilise the frequency.

The transmitter is clean enough to drive larger power amplifiers to get much higher powers. I will be working on both 5-Watts and 25-Watts amplifiers at some time in the future, but exactly when is another question. The more e-mail I get then the longer it will take. My work will be primarily for the 144-146MHz amateur radio band.

Conclusion

I hope that you learn a lot from this project. It demonstrates Varicap diode tuning, decoupling and control. It also shows how to amplify low level signals from the 10mW level to the 150mW level and how DC bias can be applied to make compensations for low signal levels. Have fun with the project. If you have any questions then please do NOT e-mail me. I have a message board where you may post questions to many, some of whom have far more experience than I.

Finally, is there any interest in my producing a kit for this project? I would include the input cap, pre-emphasis and Zener on the kit PCB, but there would be details showing how to bypass this for those who wish to do more than just send music. Please let me know at mailto:harryvpo@hotmail.com?subject=v7_kit keeping your mail short as possible, thanks.

Very best regards from Harry - SM0VPO, Lunda, Sweden.

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