Explanation of the 20dB VHF amplifier operation

[mr_byte31]

hi every body
i had made this circuit and it worked fine
**broken link removed**
i found that circuit it makes 20dB gain
https://www.electronics-lab.com/projects/rf/009/index.html
i want to connect the FM last stage with this circuit
whats ur idea?
the second question y they work with power gain not voltage gain?
3-the o/p of my FM is 20v peak to peak i am afraid it will cause saturation so it will be distorted am i right???

 

[palesha]

Re: 20dB VHF amplifier

This is very low output circuit.
It won't work for ur purpose.
Don't try the way u think. Better go for full tried & tested circuit available on net. Just google & u will find many. In RF matching/return loss is very important.

 

[mr_byte31]

20dB VHF amplifier

thank u for ur reply
what do u mean by low o/p circuit (it is 20dB gain)???
and why wouldn't it work??????!!!!!!

 

[mr_byte31]

20dB VHF amplifier

can any body help?

 

[E-design]

Re: 20dB VHF amplifier

Amplifier may have high gain but low power output. This will be determined by the 1dB compression point of the amplifier. If you use an amplifier with a -10dBm compression point and 20dB gain it will be useless with a input of 0dBm/1mW for example as the amplifier can not provide more power than -10dBm.

 

[G4BCH]

Re: 20dB VHF amplifier

The 20dB gain amplifier you refer to is basically a pre-amplifier the maximum output power that it can give is about 0.001W. It is intended for the input to a receiver, not the output of a transmitter.
Assuming the 20V you measured is across 50 ohms then your transmitter is already giving about 1Watt output. If you add a 20dB gain amplifier after this, it will have to give 100Watts.
The amplifiers performance is not just about gain it is also about a number of other requirements, output power being just one of them.

 

[palesha]

Re: 20dB VHF amplifier

to make it simple:
Every transistor has max output level. The transistor used in ur preamp r very low power devices. Hence u get low output.
To get more power u must high power devices. If u r designing any amplifier, understand the power required by the amplifier. If ur amplifier is 60 % efficient, then to get 100 watt power u will require roughly 165w power supply.
I think u must be knowing about watts.
I hv tried to explain u in simple way.