一款优秀的分立元件发射机电路(英文)

文章摘要： You will note that the 15pf capacitor coupling L1 to the BB105 varicap diode is laying on the board. It磗 legs are so formed that it acts as a link. Assembly order is not particularly important, but it is easier if all horisontal components are mounted first, then the passive components (resistors/c

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

You will note that the 15pf capacitor coupling L1 to the BB105 varicap diode is laying on the board. It磗 legs are so formed that it acts as a link. Assembly order is not particularly important, but it is easier if all horisontal components are mounted first, then the passive components (resistors/caps), transistors and the coils last. Neatness and attention to detail is particularly important. The vertically mounted resistors should all be mounted as shown on the component overlay. It DOES matter which way round they are. This is one of the prices for using a cheap single-sided board.

Testing

When all the components have been fitted, check your work thoroughly. I reccomend you shine a strong lamp behind the board component side and compare the tracks with the PCB foil pattern. This will allow you to check for solder bridges between tracks. Assuming all is well, connect a 50-Ohm resistor to the antenna (ANT) terminals. Two 100-Ohms in parallel will be fine. Now connect the board to a 9v supply in series with a 12v 3W torch lamp. If the lamp glows brightly then switch OFF and check your wiring because you have a fault. If there is no fault then the lamp should only glow dimly, if it glows at all. The complete transmitter should draw less than 100mA.

If all is well, switch ON an FM radio set tuned to somewhere around 108MHz. Adjust the tuning capacitor on the board so the plates are at around minimum capacitance and you will hear the transmitter on the radio. With the capacitor plates near maximum capacitance you should be able to tune the transmitter to 88MHz.

Now couple the AF IN terminals of the transmitter to the LINE OUT of a stereo ststem, your computer, or even the headphone terminals of your Sony Walkman. I prefer to use headphine terminals since the volume control will give you some control over the modulation depth. You can set the modulation depth by comparing it with another radio channel. Set your transmitter A LITTLE-p.htm" target="_blank" title="LITTLE货源和PDF资料">LITTLE LOWER IN VOLUME than other channels, unless you have access to a modulation meter. Note that you may have to use a capacitor in series with the AF input wire. See the application data further down.

If your transmitter is working then you can remove the test lamp and connect the battery supply directly to the transmitter. Check that nothing is burning. TR3 should get a little warm, but comfortable to the touch. All other components should remain stone cold. TR3 may get a little warmer if you increase the supply voltage to 13.8v but in this case the transmitter will be delivering almost half a watt of output power.

Performance

I think that here I should give a little information about the actual measured values of the prototype. The target was to achiece a clean 100mW of output power at 9v. I also indended the transmitter to be equally stable at 13.8v DC since this is what most constructors seem to want. The target was exceeded on all counts. There are no spurious outputs visible from 500MHz upwards, so this spectrum analyser view is only from DC to 500MHz. It shows that there is a little 2nd and 3rd harmonic outputs, but the levels are so low that they are quite negligible. I could hardly believe my eyes when I built the first prototype, but after cleaning up the PCB the output was even better! The vertical scale is 10dB per division and the horisontal scale is 50MHz per division:

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