1---
2app_version: 0.1.0
3precision: 2
4form_title: PA Efficiency & Duty Cycle Heating
5form_description: Same peak power, very different heat — compare SSB, CW and a 100%-duty digital mode on the same amplifier. Enter peak output, DC input and each mode's duty cycle.
6form_inputs: DC input power (W)|p_dc_w, Peak RF output (W)|p_peak_w, SSB duty cycle (%)|duty_ssb, CW duty cycle (%)|duty_cw, FT8/digital duty cycle (%)|duty_digital
7form_outputs: Efficiency (%)|efficiency_pct, Dissipated heat at 100% duty (W)|p_diss_w, Average heat — SSB (W)|heat_ssb_w, Average heat — CW (W)|heat_cw_w, Average heat — digital (W)|heat_digital_w
8---
9# PA Efficiency & Duty Cycle Heating
10// "The rig is rated for 100 W — why does it get so much hotter running FT8
11// than SSB at the same power setting?"
12//
13// Efficiency tells you what fraction of the DC power becomes RF instead of
14// heat. Duty cycle tells you how much of the TIME you're actually
15// transmitting at that peak level — and heat builds up from the AVERAGE,
16// not the peak.
17
18# Efficiency
19p_dc_w = 250 // W, DC input power at full drive
20p_peak_w = 100 // W, peak RF output power
21
22efficiency_pct = p_peak_w / p_dc_w * 100
23p_diss_w = p_dc_w - p_peak_w // heat dissipated while transmitting
24
25"Efficiency (%)": efficiency_pct
26"Heat dissipated while transmitting (W)": p_diss_w
27
28# Duty cycle by mode
29// Rough, commonly used figures — SSB's duty cycle depends heavily on your
30// voice and processing; CW and digital modes are far more consistent.
31duty_ssb = 25 % // typical average for unprocessed speech
32duty_cw = 45 % // typical for hand-sent CW
33duty_digital = 100 % // FT8/RTTY-style: continuous key-down tone(s)
34
35heat_ssb_w = p_diss_w * duty_ssb
36heat_cw_w = p_diss_w * duty_cw
37heat_digital_w = p_diss_w * duty_digital
38
39"Average heat — SSB (W)": heat_ssb_w
40"Average heat — CW (W)": heat_cw_w
41"Average heat — 100%-duty digital (W)": heat_digital_w
42
43// Same story for average RF output, if you care about legal power limits
44// measured as an average rather than a peak.
45avg_rf_ssb_w = p_peak_w * duty_ssb
46avg_rf_digital_w = p_peak_w * duty_digital
47
48"Average RF output — SSB (W)": avg_rf_ssb_w
49"Average RF output — 100%-duty digital (W)": avg_rf_digital_w
50