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, compared to common emitter. 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
gain = m2. [in x]
voltage Gain = 20 * Log10(m2) [in dB].
There is only one gain! Some ncdxf folks don't know that.
Voltage gain in [dB] = Power gain in [dB]. If you use dB, nothing changes.
magnet wire 0.25mm.
Vcc = 12V, Vces=0.5V, Ic= 25mA, 2N5109 from Central Semiconductor
yes, you can buy from Central Semiconductor. Check if they ship to your location..
| E [turns]
|| M [turns]
|| N [turns]
|| nominal Gain [dB]
|| Rc impedance [ohm]
|| Power [W]
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 0.5W transistor is little bit lazy, requiring higher collector current to get the gain-bandwith product. It has higher rbb resistance.
The metal case transistors are better than the plastic ones. There was a difference of 6-8 dB in IMD3 between the plastic and metal one. Same product, same parameters, 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. Transistor selection is BFR34, BFR96, bfw16, bfw30, 2sc3355, 2SD636, 2N3866 might be another choice. Check for stability from s-parameters. HF bands are so much noisy, the noise figure won't make a difference.
The IMD3 mixing products drop with lower gain, larger current (linearity), higher Vcc voltage, and 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 handling capability and the transistor delivers less power and the IMD3 products rise up. The two signal method is good enough. Ferrite limits are - maximum magnetic flux and the linearity.
I prefer ordinary transistors over the specialized HBT chips in specialized case with specialized footprint. Once the semicondonductor foundry is bought out, or belly-up, there are no spared chips.
There is a method how to measure the signal distortion using the EVM meter - 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 computer. Somebody thinks, there will be no IMD distortion in the DSP unit, and I can get rid of these transformers replacing them with the 300mA or 500mA drivers and buffers with noise figure of 15. You will see the intermods and the image, as well.
The HF signal power levels used for measurement require power splitter, that can handle the power. Every ferrite material is different. Simulation is useless. Consider Fair-Rite, MuRata, TDK ferrite materials, Neosid, Wurth. I got a nice two hole ferrites from Houston, Texas store. Strongly recommend that. Nice people, flexible attitude, good pricing, full service, in few days you will get it by surface mail.
The following article from ARRL is a description of consequences, and selection of a VHF/UHF transistor for HF frequency band.
All RF bipolar transistors have a low frequency region with very high gain. It looks like rabbit ears. Then the gain drops, and follows datasheet values starting at 500MHz. It is useful to check the s-parameter matrix for stability circles at the band of interest, and close by. Mostly the s-parameter table starts at 500MHz. Recent semiconductor manufacturers do not deliver any low frequency s-parameters any more. Enjoy the discussion what transistor is the best choice. Push-pull configuration with 5GHz transistors oscillates...
Epcos toroidal ferrite cores
warning: The edges of the ferrite cores are sharp. Epcos ferrite material conducts DC current. Sharp edge will cut the magnet wire insulation, resulting in shorted turns. Epcos manufactures in third countries..
Norton amplifier ARRL.pdf
 VA3DIW Dave's notes
 U.L. Rohde: Digital PLL Sythesizers
 Lankford: Common Base Transformer Feedback Norton Amplifiers
 Futurelek.com - smd and leaded RF transistors
MADE IN USA
The IMD3 test signal source board is available for swap. Three boards left.
Build your IMD3 tester during weekend.
Two by two inches board.