This calculator calculates some key values for operation of a valve RF amplifier with resonant load, and points on an intitial load line for further modelling with the Designing the operating point for a grounded grid Triode Class B RF amplifier.
Key assumptions of the calculator are:
Class AB RF amplifiers usually operate so close to Class B conduction angle that Class B assumptions are quite reasonable for an initial load line estimate, in fact the greatest source of error is the device non-linearity rather than conduction angle assumptions.
The method used by this calculator is described in detail at Designing the operating point for a grounded grid Triode Class B RF amplifier.
The calculator does not do a lot of error checking, if you enter nonsense, it will produce nonsense. NaN means not a number, check the input values.
All values are peak unless annotated otherwise. RF annotation means Radio Frequency component at the fundamental frequency.
|Vs||Anode DC power supply voltage (loaded)|
|Vgk||Peak grid - cathode voltage (not required
for common cathode configuration)
|Vak min||Minimum instantaneous anode - cathode voltage|
|Vk bias||Cathode bias voltage|
|Po||Required RF power output|
|NWeff||Output network efficiency (typically ~95%)|
|Class||Amplifier class (A, B, C)|
|Configuration||Amplifier configuration (CC, CG), single ended or push-pull|
Calculated values are per device except Rl which in push-pull configuration is anode to anode.
The ARRL Handbook has a formula with a bunch of K factors for different
classes, and they explain
K = a constant that approximates the (fundamental) RMS current to dc [sic] current ratio
appropriate for each class. Their factor K captures more than that, even if
poorly. Their method implies that Vak min is proportional to DC supply voltage,
but it isn't. The ARRL method is not sensitive to whether a PA is common cathode
or common grid configuration. The method described in this article and used in
the calculator is a more accurate model than the ARRL formula.
Many other design tools are based on the ARRL's method and K factors, or similar.
|1.02||01/02/2014||Added push-pull option.|
© Copyright: Owen Duffy 1995, 2016. All rights reserved. Disclaimer.