Homebrew | Coding Challenge
Initiated and sponsored by OM Ram Sankar, VU2RWH
This challenge is for licensed amateur radio hams only.
Prior registration is required for participation. Please select the Homebrew challenge option while registering online.
The homebrewer should bring the linear amp to Mahameet on 14-Feb-2026 for evaluation.
Functionality is the main criteria. Fit and finish will not be deciding factor.
Jury members will be announced later
Initially it was announced that the challenge was to build a 40 Watt linear amp using BJT. After considering the feedback from homebrewers, modifications have been made to the challenge
20 Watt and above - the challenge is to build a linear amp giving at least 20 Watt output.
IGBT can be used.
DC-DC voltage converter can be used for the finals
Additional help regarding the use of IGBT and DC-DC converters in RF amplifiers have been added to the resources section below
Paddle Key for 1 person
Straight Key for 2 persons
Prizes sponsored by OM Ram Sankar, VU2RWH. Details of the keys can be viewed at https://hamradioshop.in/
Any kind of BJT can be used, but expecting designs with available transistors in India, so that other Hams can replicate the design and use.
Any kind of circuit combination is allowed. Single end, push-pull, paralleled single, paralleled push-pull or combined output.
Supply voltage to be limited to a maximum of 25.2 V. The idea is to make it usable with Lithium Ion battery . So 6 x 3.7v = 22.2V to 25.2V
There is no limit for power consumption.
There must be a third order, fixed/tunable low pass filter at the output.
Power will be measured after the low pass filter.
Any CLASS allowed.
Input power 500mW to 1 W across 50ohm PAD
All measurements will be carried out with a 50 ohm dummy load connected
Measurements
DC power in
RF power output - with input signal at 7.0 MHz
RF power output - with input signal at 7.1 MHz
RF power output - with input signal at 7.2 MHz
RF power output - without input signal
Spurious emissions and self oscillations should not be present.
Output power should be steady and the amp should withstand continuous key down for 120 sec
BJT: Bipolar Junction Transistor https://en.wikipedia.org/wiki/Bipolar_junction_transistor
IGBT: Insulated Gate Bipolar Transistor https://en.wikipedia.org/wiki/Insulated-gate_bipolar_transistor
Third-order filter: "A third-order filter requires at least three reactive components: one capacitor and two inductors, two capacitors and one inductor" - quoted from https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Operational_Amplifiers_and_Linear_Integrated_Circuits_-_Theory_and_Application_(Fiore)/11%3A_Active_Filters/11.04%3A_Section_4-
Designing and Building Transistor Linear Power Amplifiers Part-1 : https://www.arrl.org/files/file/QST%2520Binaries/QS0209Campbell.pdf
Designing and Building Transistor Linear Power Amplifiers Part-2 : https://www.arrl.org/files/file/QST%2520Binaries/QS0309Campbell.pdf
RF Power Amplification Using a High Voltage, High Current IGBT : https://www.arrl.org/files/file/QEX_Next_Issue/2014/May-Jun_2014/Horowitz.pdf
More power with a dc to dc converter : https://www.youtube.com/watch?v=DVns2w8QM4s
Basic Linear Amplifier: http://sm0vpo.altervista.org/tx/rf_pa_cct_00.htm