The Norton Amplifier

The Norton amplifier has very good performance.
It is sort of CATV amplifier. The gain is flat. For HF the input impedance is little bit higher than 50 ohms. The gain is selected by turns ratio in the collector circuit. For VHF the input impedance is lower and needs some match. The isolation s12 is good up to few hundreds MHz, it can work in broadband mode from 2 to 200MHz.
On the lower frequency side, the frequency limit is set by the transformer inductance and capacitors.
The upper frequency side is set by the ferrite output transformer and collector capacitance, including s21 drop. It can cover few octaves and reach decade or two. The noise figure is good. Common base configuration has extended dynamic range in terms of P1dB compression, IMD3, and IP3. The transformer turns ratio is:
N = M2 - M -1.

N ... collector to output tap turns
M ... output tap to Vcc turns
E emitter input ... one turn, for lower gain oriented
The power gain equals to m2.

Vcc = 12V, Vces=0.5V, Ic=2x 25mA, 2n5109, Central Semiconductor
  E [turns]   M [turns]   N [turns]   nominal Gain [dB]   Rc impedance [ohm]   Power [W]
  1   2   1   6.02   150   0.880
  1   3   5   9.54   400   0.330
  1   4   11   12   750   0.176
  1   5   19   13.9   1200   0.110
  1   6   29   15.56   1700   0.085

The "E" input has one turn. If you swap the input wires, the amplifier will give higher gain - that's wrong. Oscillation.
The collector turns "N" ratio commands the gain. "M" goes to the Vcc. Select gain 6dB, 9dB and count with 0.5dB loss in the ferrite.
Consider the input transients from antenna with amplitude of plenty volts, then the ESD, then the lightning. I believe RF medium power bipolars are more rigid for this application. The 5GHz transitors are mostly unstable in the HF region.

You might find similar designs with the feedback in the emmiter. Another 3-4 similar configurations with transformer are used in cable tv CATV networks. I compared 2N5109 with 2N2222. The 2N2222 is little bit lazy, requiring higher current to get the gain-bandwith. It has higher rbb.
The metal case transistors are better than the plastic. There was a difference of 6-8 dB between the plastic and metal in IMD3. Same product, different case. The plastic does not dissipate more power than the metal can and has higher thermal resistance. The input was fed by IMD3 test signal generator delivering two input signals. The BFR34, BFR96, bfw16, bfw30, 2sc3355, 2N3866 might be another choice. Check for stability from s-parameters.
The IMD3 mixing products drop with lower gain, larger current (linearity), higher Vcc voltage, lower input power overload, better linearity transistor. Use of higher voltage will improve the IMD3 in single digit dB. If you drop the current, naturally there is less output power capability and the transistor delivers less power and the IMD3 products rise up. The two signal method is good enough.
I prefer transistors over the specialized HBT chips. Once the semicondonductor foundry is bought out or belly-up, there are no spared chips.
There is a method how to measure the distortion using the evm - error vector magnitude for linear signals such as OFDM and QAM. Most of the companies rarely rent this machine. It is a small desktop mainframe.
The HF signal power levels used for measurement requires appropriate power splitter that can handle the input power. Every ferrite material is different, it requires test setup. Simulation is useless. Consider Fair-Rite, MuRata, TDK ferrite materials, Neosid, Wurth.

The following article is a description of consequences, and selection of a VHF/UHF transistor for HF frequency band.
All RF transistors have a low frequency region with very high gain. Then the gain drops, and you get the gain and stability values same as the datasheet says, starting at about 500MHz. It is useful to check the s-parameter matrix for stability circles at the band of interest, and around. Mostly the datasheet s-parameter table starts at 500MHz. Recent ten years the manufacturers do not deliver any low frequency s-parameters any more. It looks like, there are no people to measure it.
Enjoy the discussion what transistor is the best choice.

Norton amplifier.pdf


[1] VA3DIW Dave's notes
[2] U.L. Rohde: Digital PLL Sythesizers
[3] Lankford: Common Base Transformer Feedback Norton Amplifiers
[4] Futurelek - smd and leaded RF transistors without sales cartel embargo

Made in USA
The IMD3 signal source board is available for swap. Three boards left.