1W Frequency Modulation (FM) transmitter production
FM transmitter has been making a bundle of interference problems for beginners, starting with the transistor can not start oscillating and because of the power is too small, too short distance. Recently, various books, magazines have a lot of FM transmitters on the production of the article, I have tried, to little success, let alone to describe the distance between them, and I recently had a successful trial launch machine, and now share with everyone!
The machine features: 1. Easy to start oscillating
2. Frequency stability (of course compared to crystal or have a certain gap)
3. Can very easily by adjusting the coverage of the entire FM band
4. Make easy, simply debugging can achieve satisfactory results
5. Launchers around 2KM distance of open area for the non-open area for the> 500M
First talk about the various parameters. Frequency of 88MHz-108MHz (adjustable), operating voltage 12V (DC), machine current 300mA, machine power is about 3.6W, transmit power 1W, certainly a friend to ask why such a big machine power and transmission power only 1W. Is very simple, because the oscillation and promote a total of 1W of power consumption, final amplifier is only 2.6W of power, which is being converted into heat 1.6W lost lost (a lot of information on said 2SC1970 5-watt tube, this is true, but what is the tube 5W total power consumption is not to say it's transmit power, in fact, the transmitted power is only 1.3W 2SC1970 about the same as 2SC1971 have more than 10 watts power consumption and emission power only 5W, we must not mistake).
We say that the choice of transistors, FM with MV2105 (varactor diode) If can not find the MV2105 through a 40K resistor directly to the 9018 as the base of the can, shaking with 9018 on it, if you want to increase the The power level can also consider using C8050, I used 8050 in the production process, the power is significantly increased, but at the expense of frequency stability and audio quality. Promote the level with the C3355, it is 0.6W tube, to provide 100-200mW output power, can be easily driven by an amplifier has. PA-level selection 2SC1970, everyone should know that it could see us 1W output is surely can do it! If you find the actual work process is very hot radiator 2SC1970, state your transmitter circuit debugging is not good, if tuned in, the radiator there is a certain temperature but not very hot, if the change can 2SC1970 into 2SC1971, its power can reach 2W or so. There is also a way to increase power is to increase the voltage as 13.5V but preferably not more than 14V, or it may burn out pipe!
Finally, we talk about the antenna, you can choose to J-type antenna or a half-wave dipole antenna, cross-shaped antenna, etc. If they could choose the direction of double-cross-shaped antenna that all the effects are better. Erection of the antenna is closely related with the distance, the general require more than 10M high, with a 75Ω cable (that is normally closed household line) connection. I have done this experiment the half-wave dipole antenna on a building in and not out of the house, housing is a reinforced concrete structure and the installation of a fence, surrounded by buildings, so the conditions are very harsh on the transmitter The results show launched from the remains> 500 meters.
Another wordy one, due to higher transmission power the machine, ladies and gentlemen in the production test process consciously abide by relevant laws and regulations!
If in the production process have any questions, welcome and owners to discuss!
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