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first of all you shoul know some basic rules:
1.noise factor of the first stage of the amplifier make the noise factor of the whole amplifier
2.for uhf and especialy the upper band of the uhf the coil have to be "silvered" as long as the case of the amplifier
3.beware of the power source by the antenna (the amplifier is powered thrught the antenna cable)
4.the condensators should have the shortest terminals (you can strip them from their ceramic capsule)
5.the parts soldered together (in air) work good -and sometimes better that them soldered on pcb-
there are 3 tipes of transistors used in rf amplifiers.
mosfets -good amplification and noise factor-bf981-bf961...be careful when you solder them,use ground because they are sesible on electrical discharge
calsical npn-pnp bfy90 bfr91 supports a lot more curent than mosfets
fet
so when you will find a schematic look in the datashet of the transistor to know what you are dealing with (noise factor,amplification)
the best amplifier has on his first stage a transistor with the lowest noise factor (e.g bfr91a ) and for the second stage use a mosfet(good amplification ~20db e.g bf966)
the best amplifiers are from old lnb(sat convertors).you can buy them for nothing and ahve a good extended band amplifier.
for schematics look on post on electroda about ham sites or search them for youreself.btw what are you interested? dx reception or power amplifiers(like catv amplifiers)
Here are several suggestions. First, if you are not experienced in this frequency range and do not have access to test equipment, you will probably be better off buying a ready made consumer product. It is too easy to make an oscillator instead of an amplifier if you are not careful.
If you want to try anyway, use commercial broad band modular amplifier blocks that are unconditionally stable. That is, they are guaranteed to not oscillate with any possible source and load impedance. Minicircuits is a good supplier of cheap modules.
If the module has a noise figure equal or greater than the sum of your receiver noise figure plus the loss in the transmission line, you will get a worst signal at the receiver than if you did not use the amplifier. Select a module with a noise figure at least 3 dB lower than this sum and gain of 6 dB or more than the line loss.
Using lower loss transmission line will always improve things. A directive gain antenna also improves things.
If you have an inexpensive receiver, you may be bothered with intermodulation products due to the higher signal level produced by the new amplifier.
Thanks.
I have access to 2SC4093 & 2SC4094 for input & 2SC3355 for output stage. I can get tested from my friend's company. I was looking for some circuits if used by fellow members which can be of help to me and don't want other's to do donkey work. In google i just got all booster manufacturer and installation notes.
MP
If no one can supply you with a circuit, your best bet would be to thumb through amateur VHF handbooks. Unfortunately, data sheets from European and Asian companies do not include example circuits any more. Data sheets and application notes from US companies have typical circuits for their transistors which are not the 2SC series.
There are a lot of RF circuit ideas at the following URL, including a UHF amplifier:
h**p://www.commlinx.com.au/rf.htm
(*=t)
You might also try looking for application notes using Google or Altavista - several manufacturers make RF amplifier chips that require just a few supporting descrete parts.
It seems nobody mentioned an important point.
Ground connections should be as short as possible.
All ground connections should be connected to ground plane through shortest path.
This topic is viewed by so many members. But till now can't see circuits here. Why not develop the circuit here as diyaudio members do in audio. I think many of us will be interetsed. We can start by selecting some common RF device easily available everywhere. Then members will design, few will make prototype. Then final design.
This is most simpliest VHF/UHF amplifier ,it is build with excellent BFR91A.
I build several this antenne amplifiers and all my freiends tell that work very well.
as you refer to BF966, old but very good transistor, I decided to ask you about the spice model. Do you have it or can you help me to find it? I have the one for BF988, but I have some BF966S and I want to use them. Actually I prefer to build and simulate the circuit by a pSpice tool and then to have the real performance. Please, if someone can help do not hesitate to contact me or just to post the spice model data here in the forum.
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