Topband: Norton preamp

[andy.ikin at btopenworld.com]

Steve  Wrote
> Has anyone tried one of these preamp designs?
> I cannot make sense of the use of the extremely hi-mu FT-50-75 cores in 
> this design.
>
> http://www.kongsfjord.no/dl/Amplifiers/Ultralinear%202N5109%20And%202N3053%20Amplifiers.pdf



Steve,



I have made hundreds of balanced Norton amplifiers, ones where the windings 
are consolidated onto just two fair-rite 28430000302 twin hole cores. Also I 
have experimented with the 4 transformer versions using the above core. The 
1995 ARRL HB, pages 15.27 and 15.28 describes N6NWP High Dynamic Rage Front 
End. This describes the twin hole core winding details for an 8dB gain 
Norton. For the 10/11dB version, use the 1:11:4 winding ratio for the 
collector/emitter transformer.



You may need to fit a ferrite bead to the transistor base to prevent VHF 
instability.



Recommended transistors are, 2N5109, 2N4427, 2N3866, MRF586 etc.



With the Dallas circuit, you should have no problem in achieving an IOP3 of 
+45dBm, but you may need to carefully adjust the transistor bias to get on 
IOP2 of +80dBm.



If you intend to use this amplifier or any other amplifier with a broadband 
antenna input, a high IOP2 is just as important as having a high IOP3. This 
is because the second order intermodulation products can degrade reception 
before the third order intermod. is noticeable.





Good luck with your Norton.



73



Andy G8LUG (not active)