Re: [EVGRAY] Re: ? using LNA for front end of PA

Body

Ole,

Yes I understand this part about building according to these RF rules,
just wondering if the theory is correct or if I am missing something
from my topology.

Thanks for the links, I already bought one of these but before I found
it I was contemplating what I asked you.  I have no idea how they build
an amp that is so wideband, how they come up with the trace lengths to
satisfy VHF to Microwave other than most of it resides on a chip with a
much shorter wavelength than the chip process dimensions.  They still
have to connect to the output device through traces of a certain length,
so how do they choose the trace length besides as short as possible?

I am sure the capacitance of the PCB is also a factor that has to be
taken into account.  Can't just put a huge ground plane on one side like
we do in audio.


On 3/26/2018 3:53 AM, [email protected] [EVGRAY] wrote:
>  
>
> Hi Mick,
>
> At those frequencies the energy is very radiant. Everything has to be
> made according to RF rules and treated as transmission lines. Else the
> signal doesn't follow the signal path as planned. Any change in
> impedance reflects or splits the signal. Read Ivor Catt on this even
> though he explains it using digital signals. If attaching a current
> buffer everything has to match. I haven't worked on such high
> frequencies. If trying this at least know the theory behind it or have
> the measuring instruments for this frequency range.
>
> This site (http://nov79.com/amr/cont.htm) shows how to make a simple
> current amplifier by using matched bipolar transistors. The upper
> frequency is only limited by the upper frequency of the transistors.
> This can be 40MHz for an audio amplifier. This may cause oscillations
> at the max frequency if not done the correct way.
>
> What about a small 3W broadband power amplifier module:
> https://www.ebay.com/itm/1-1000MHz-3W-RF-Broadband-Power-Amplifier-Module-Radio-Transmission-FM-VHF-/183031453375
> It only goes to 1GHz.
>
> Google search for 'broadband power amplifier module':
> https://www.google.dk/search?source=hp&ei=c8G4Wuv0LIXbwALZxJTQDw&q=broadband+power+amplifier+module&oq=broadband+power+ampli&gs_l=psy-ab.3.2.0l2j0i22i30k1l8.1878.9748.0.22828.21.20.0.1.1.0.104.1822.18j2.20.0....0...1c.1.64.psy-ab..0.21.1820...46j0i46k1j0i10k1.0.jIuIG0_77XA
>
> Or search 'rf power amplifier module'
>
> Regards
> Ole
>
>
>
> ---In [email protected], <mkjekyll@...> wrote :
>
> Ole,
>
> What would be the negative issues trying to attach a FET current buffer
> to an LNA in order to make a few watt wideband RF amplifier?
>
> As I am an audio guy I am paralleling this to an audio amp seems simple
> a voltage gain stage and then a current gain or buffer stage.
>
> There are plenty of cheap LNA's that are very wideband like this 
> https://www.ebay.com/itm/New-1MHz-2GHz-64dB-Gain-LNA-RF-Broadband-Low-Noise-Amplifier-Module-HF-VHF-UHF/232103825103?hash=item360a774ecf:g:iCQAAOSwgu9ZZEBg
>