What P1dB has a 2N5109 transistor?

This depends on the circuit, especially current, voltage, type of biasing, frequency,etc. These transistors were designed for CATV applications (requires good linearity) and are found in many amateur applications.

Just a guess: it should be possible to make an amplifier with P1 dB > 300mW with this transistor.

This home-made amplifier;

http://i40.tinypic.com/34qkciv.jpg

has a 5109 final with Ic 50mA; as you can see, P1dB is +25dBm.

A very good guess, Wim!

Thanks!
My experiment is: Inpunt 21dbm -> Out 28.8dbm (max) at 12Vcc and Out 30.7dbm with power 15Vcc

Overall gain seems a bit low but power-out is probably about-right with 15v and, perhaps, 100mA Ic.

You would require a larger heatsink than the one that I used;

http://i40.tinypic.com/344ceja.jpg

In fact I have a low gain, but if I insert in input 10dBm and NOT 21dbm I have 22dbm in out +12dbm of gain.
Therefore the input of 21dBm is too large for this transistor? because I have only 6-7dbm of gain

my experiment is video/audio modulator for tv 224.5 Mhz
my demo board

It sounds as if you are over-driving the transistor.

I would expect about 10dB of power gain under normal conditions.

In short; yes, +21dBm is too much input.

Hello,

I assume you have a class A amplifier. When you increase the input drive, two things can happen:

Collector voltage may clip so the transistor will go into voltage saturation (BC diode will conduct during negative collector voltage swing).

Collector current may clip, so the transistor goes fully off during the negative voltage swing of the base voltage.

In case of voltage saturation (this may lead to an increase in base bias current or drop in DC base voltage), reducing the load impedance, as seen by the collector reduces the gain, but increases the linear output power.

When your base bias circuit isn't stiff (say low DC impedance), you will notice reduction in base voltage with increasing RF input. This is a sign that the transistor is leaving class A and goes towards class B, or even Class C with large RF input.


I agree with krp that 21 dBm real input power is too much for this transistor.