Re: Grounded grid VHF front-end

On Sun, 10 Nov 2024 09:33:05 -0500, Ralph Mowery
<rmowery42@charter.net> wrote:

In article <1r2sqh1.puusef1eope1aN%liz@poppyrecords.invalid.invalid>,
liz@poppyrecords.invalid.invalid says...

 
 

Tubes are noisy. There are MMICS with NFs below 1 dB.

 
There are quiet valves (Nuvistors) and noisy transistors (many),
engineering is a matter of chosing the right ones or using them in a way
which minimises the noise or makes it less significant in the overall
design.
 
 

>
Once you get above say 100 MHz the tubes that are common do not have the
noise figure of very cheap solid state devices.  A nuvistor at 150 MHz
will do good to prodce a noise figure of 3 dB.  A cheap fet like a U310
will have a noise figure of less than 2 dB and the power supply will be
much cheaper to build. Going to cheap gasfets get you to under 1 dB of
noise figure.  At this time I just do not see why anyone would want to
use tubes in a receiver above 50 MHz if they want a sensitive receiver. 
>
Years ago I had an Ameco receive converter for 2 meters.  It used
nuvistor tubes.  Worked fine but I put a u310 fet preamp on it and it
was noticable beter.

A cheap MMIC from MiniCircuits will get down to 1 dB, and it's 4 pins,
in  out  2 grounds,  fabulously simple.

I use their MMICS in time domain, as pulse amplifiers.  Most - not all
- work fine down to DC.  As is some Federal law with RF parts, the DC
specs are absurd so you have to characterize them yourself.