Can this RF Amp dissipates 5 watt just feeding 100 or 200mW??

[Willen]

what are they saying?
www.electronics-diy.com/electronic_schematic.php?id=1068

 

[ronsimpson]

I would not use the word "dissipate".

They say:
0.1watt to 0.2 watt into the amplifier and 5 watts out.
The power gain is 50 to 25. The voltage gain is 7 to 5.

Looks OK to me.

 

[Willen]

I would not use the word "dissipate".

They say:
0.1watt to 0.2 watt into the amplifier and 5 watts out.
The power gain is 50 to 25. The voltage gain is 7 to 5.

Looks OK to me.

It makes me amazing! I have found some '5 watt amp circuits' but they feed 1 watt RF and produce 5 watt RF. But why this one is so special that feeds ONLY 200mW and produce 5 watt? Why it is too great?
Are there any special reasons? Please
And another question:- If I feed it with 400 or 500mW (with matching trimmers), what will be the result?

 

[ronsimpson]

If you over drive the input the output will distort.

 

[ronsimpson]

If you over drive the input the output will distort.

The amp is class C so the output is distorted, but I am talking about peak clipping.

 

[Willen]

If you over drive the input the output will distort.

The amp is class C so the output is distorted, but I am talking about peak clipping.

are there any idea to control this type of Over Drive? (some circuits or links?)

 

[davenn]

yes, keep your drive levels within the specifications of each device in the amplifier chain.
a good accurate power meter is ideal for that to measure power levels generated by each stage

Dave

 

[ronsimpson]

On big amplifiers I measured the amount of power in the carrier frequency (100mhz) and at the first harmonics. (200mhz, 300mhz, 400mhz) If the amplifier was over driven the power in the harmonics went up. I know you don't have a way to do that.

If you plot a graph of input power and output power you will find a point where more drive does not get you more power out. Stay away from that point.

 

[Willen]

On big amplifiers I measured the amount of power in the carrier frequency (100mhz) and at the first harmonics. (200mhz, 300mhz, 400mhz) If the amplifier was over driven the power in the harmonics went up. I know you don't have a way to do that.

If you plot a graph of input power and output power you will find a point where more drive does not get you more power out. Stay away from that point.

Does an attenuator help me to low down the over drive RF? I know nothing about such attenuator

 

[ronsimpson]

Yes. Attenuator will reduce the size of a signal.

 

[Willen]

Yes. Attenuator will reduce the size of a signal.

can you give me any exact circuit suitable for this purpose.

 

[WTP Pepper]

Your posted circuit does not contain any DC bias on the input so I assume it's Class C. Overdriving the input will distort the signal but if it's constant carrier (e.g FM) you just produce more harmonics. If correctly filtered and you don't cook the transistor in the process, it should work fine.

If you need a linear circuit for SSB or AM then your circuit is a no brainer.

You can clamp the input using PIN diodes back to back to prevent overload.

https://www.electro-tech-online.com/custompdfs/2012/07/dioxref.pdf

 

[ronsimpson]

The application is FM.

There are two 40pF caps on the input. I think by changing the ratio of the caps should change the attenuation.
If the input cap is adjusted to 4pF and the cap to ground is set to 40pF then only a small amount of the input signal reaches the transistor. If the adjustment is reversed, 40pF and 4pF then most of the input signal reaches the transistor.

There should be information in how to set the four capacitors.

 

[ronsimpson]

What circuit? Please attach a circuit.

 

[KJ6EAD]

Post #14 is a copy/paste from https://www.w8ji.com/electronic_bias.htm.

 

[Willen]

I would not use the word "dissipate".

They say:
0.1watt to 0.2 watt into the amplifier and 5 watts out.
The power gain is 50 to 25. The voltage gain is 7 to 5.

Looks OK to me.

Hi, here is a small 'nH' RFC in series of 13.8V supply. But i think if I replace it with large RFC like '50uH or 100uH' then it will perform better, isn't it?

 

[Mikebits]

Your posted circuit does not contain any DC bias on the input so I assume it's Class C. Overdriving the input will distort the signal but if it's constant carrier (e.g FM) you just produce more harmonics. If correctly filtered and you don't cook the transistor in the process, it should work fine.

If you need a linear circuit for SSB or AM then your circuit is a no brainer.

You can clamp the input using PIN diodes back to back to prevent overload.

https://www.electro-tech-online.com/custompdfs/2012/07/dioxref.pdf

Clamping just pre-distorts the signal prior to amplification, this just makes for a bad idea (distortion in, distortion out). PIN diodes make great attenuators when configured as in image below. Maybe that's what you meant, not back to back.

View attachment 66181

 

[Mikebits]

Is it legal to build a 5W FM band transmitter?

 

[Willen]

Is it legal to build a 5W FM band transmitter?

It is legal to build 5 watt FM Tx but it is illegal to transmit.

 

[Mikebits]

It is legal to build 5 watt FM Tx but it is illegal to transmit.

So why bother? Why not make a transmitter in the amateur band?