Only about transistor amplification..pls guv me some tips...

[aj_silverthunder]

guys,what would be the range of transmission of this schematic...can it reach 20meters or higher.
with a antenna at a height of 30meters high ....
i have used a C-Class amplifier as last stage,and have used bypass cap for the 2nd and 3rd stages...
please please tell me are there some errors in it and please give me some tips...
thank u in advance...

 

[fcfusion]

Re: Only about transistor amplification..pls guv me some tip

You should have posted more information about the circuit.

Anyway, this is a FM modulator with Power amplifier, right? Frequency around 50 MHz?

Yes, in my opinion, the circuit might reach well over 20 meters. Your circuit looks like it can deliver a several output Watts. As long as it works, of course.

I've done a project like this once: an AM modulator (gilbert), carrier frequency of 2 MHZ, without power amplifier, mounted on a breadboard and the antenna was a short wire (way too short!). And it worked, I could listen to my own transmission with an old radio (shortwave receiver) across the street.

That makes me think that you won't even need a 30 meter antenna to achieve a 20 meter range. If you use such an antenna, with all that output power, you'll be transmiting to a very wide range. More than you are legally allowed too .

Don't use it for too long

 

[aj_silverthunder]

yes the transistors get's very hot,so there should be a good cooling system like heat sink for the transistors and a Air cooler mounted near the circuit....
do u think that works

Added after 42 minutes:

and guys some one please tell me how can i delete threads....please let me know

 

[snafflekid]

If you had a 30m antenna and need to reach 20m, you could just run a 20m wire and save the other 10m

 

[fcfusion]

Re: Only about transistor amplification..pls guv me some tip

If you had a 30m antenna and need to reach 20m, you could just run a 20m wire and save the other 10m

LOLOLOL

yes the transistors get's very hot,so there should be a good cooling system like heat sink for the transistors and a Air cooler mounted near the circuit....
do u think that works

Yes that will work. But if you don't need so much output power you could reduce it and save the trouble of mounting a heat sink and cooler.

 

[aj_silverthunder]

If you had a 30m antenna and need to reach 20m, you could just run a 20m wire and save the other 10m

good sense of humor>>>>

Added after 2 minutes:

2)the collector voltage goes more than the supply to the collector when there is a inductor load(inductor coil made by #18 guage CU wire) at the collector,if the value of the inductor is increased then the Vc will also increase...cause when the transistor goes to OFF Phase,then the energy stored in the collector inductor is released,which increases the voltage at the collector.So its better to keep the Vc of the transistor about half of the max Vceo of the transistor,then it will not lead to any damage of the junctions or the transistor
for EX:- A transistor 2N2219 has 40V Vceo,so the Vc should be about 12V to make sure the flyback voltage from inductor wont damage the transistor.....
to over come this problem can use protection diode,across the inductor..

Added after 37 minutes:

protection diode can protect a transistor which has a Inductor or a relay at its collector... if a diode is places across the inductor,i think like this one in the image(diode D3) " https://obrazki.elektroda.pl/15_1274548562.jpg "
but the diode limits the voltage swing at the collector.
It(diode) will conduct electricity when the voltage across its terminals reaches a certain value.
and can u please tell me how can i know that from the datasheet(of a diode),the voltage value till it can conduct and if the voltage increases it will become open circuit to protect the transistor from high voltage damage...
help me out...

 

[WimRFP]

Hello,

To do 20..30m, you just need about uW radiated power, so an oscillator with a buffer (to avoid frequency drift when approaching the antenna) will do the job.

When your oscillator supplies about mW, you can just add an attenuator to reduce drift when approaching the antenna.

The 2N3635 is a PNP transistor, so will not work in your circuit. For me it is very strange that you need an expensive 30W final transistor.

The decoupling in the emitter looks also strange. There is no decoupling between the power supply of the stages, you will probably get parasitic oscillation via power supply feedback.

I would strongly discourage to use this circuit. When it misbehaves it may generate significant power at undesired frequencies that may put you into real trouble (depending on nation).

 

[aj_silverthunder]

yes there is no RF filter to in the power supply,a RF choke of 10uH and with some capacitors grounded will do the job.....
and 2N3498 can be replaced by 3635,....

Added after 14 minutes:

As many of them said it would reach several Kms of range,but i dont need too much,so i'm not gonna build this one and thank u for u r comments wimRFP.thank u guys

Added after 3 hours 5 minutes:

guys do u think the D1 Varactor is biased by 5 volts or not......in this schematic.