Tunable RF coils question

[audioguru]

Some Oriental S8050 transistors are NPN and others are PNP. I think the translation messes it up.
It has the same max heat dissipation of 625mW (not 1W) as nearly every other little transistor in a TO-92 case.

But in your circuit the 100 ohm emitter resistor limits the average current to only 28mA so the heating is not much and the output power is very low.

 

[Ziddik]

so should i change the 100ohm to a smaller value to get more range?(2km is morethan enough for me tho)

 

[Ziddik]

https://pcs-electronics.com/schematics/TransistorDatabase.htm says 1w(search for s8050 in that page for ease)

 

[audioguru]

so should i change the 100ohm to a smaller value to get more range?(2km is morethan enough for me tho)

Reducing the emitter resistor value will try to cause increased current but the simulations I posted show that the transistor is badly clipping because the current is already as high as it can go.
If you increase the supply voltage then the range will be more.

https://pcs-electronics.com/schematic...orDatabase.htm says 1w(search for s8050 in that page for ease)

The list is wrong for the very common American 2N3904 and 2N3906 so maybe it is also wrong for the S8050.

 

[Ziddik]

I simulated the circuit made by S!dd!k.
I increased the value of the tuning capacitor by 5pf to 20pf due to stray capacitance and to reduce the frequency away from the aircraft band to the FM broadcast band.
I used a powerful 2N4401 transistor.
The oscillator stops when a load on its collector is less than 680 ohms so its output power is very low.

I added an RF amplifier transistor to isolate the antenna from the oscillator. The oscillator stops when the RF amplifier is cap-coupled to its collector but works fine when cap-coupled to its emitter. The RF amplifier drives the 75 ohm 1/4 wave antenna. The output power is low but useable.
The output has strong even harmonics which will cause interference to communications.

it's true, The oscillator stops when the RF amplifier is cap-coupled to its collector, so i will try to connect to emitter, but the rf amplifier gets hot when i power it with 9V, why is that? Maybe i need a resistor in the emitter pin?

 

[audioguru]

it's true, The oscillator stops when the RF amplifier is cap-coupled to its collector, so i will try to connect to emitter, but the rf amplifier gets hot when i power it with 9V, why is that? Maybe i need a resistor in the emitter pin?

My FM transmitter is almost the same circuit as yours in post #17 and its RF amplifier transistor gets warm, not hot.

 

[Ziddik]

i will design a circuit soon based on these great transistors and will be posted on my blog
https://Ziddique.Wordpress.Com
please take a look to my site whenever you get time and prove me if there is something wrong