Re: Topband: pHEMT and MOSFET preamps and 1/f noise on 160 meters

["Richard (Rick) Karlquist" <richard@karlquist.com>]

On 9/22/2015 12:43 PM, Art Snapper wrote:
> I have another preamp that uses an old MRF-904. Have you characterized that
> transistor at 1.8MHz? Is it worth replacing with a 2N5109?
>
>
> Art
The MRF-904 in an antique microwave transistor.  I can't
imagine why anyone would use that device at 1.8 MHz.  Those
old transistors had a lot of base spreading resistance, often around 50
ohms.  The 2N5109 is part of the 2N3866 family.  What was special
about those devices was low base spreading resistance, maybe
5 ohms or so.  This parameter, along with HF current gain, determines 
NF.  The big geometry should give better dynamic range and linearity.
Rick N6RK
_________________
Topband Reflector Archives - http://www.contesting.com/_topband