fix(elecraft): the K3 power meter converts to real watts

The operator measured the whole table: 10 W showed 83, 12 W showed 100, 13 W
showed 8 — the bargraph is relative to a meter RANGE that flips at 12 W
(0-12 QRP, 0-120 above). A bar percentage was never watts; with the PC
setting choosing the range, it converts, and the console prints the watts
beside the bar.

internal/cat/kenwood_panel.go

@@ -52,9 +52,15 @@ type KenwoodTXState struct {
 	SMeterRaw int `json:"s_meter_raw"`
 	// PowerMeter is 0-100 while transmitting. SWR is the ratio; 0 means "not
 	// measured", NOT a perfect match.
-	PowerMeter int     `json:"power_meter"`
-	SWR        float64 `json:"swr"`
-	SWRRaw     int     `json:"swr_raw"`
+	PowerMeter int `json:"power_meter"`
+	// PowerW is the transmit power in WATTS, derived from the bargraph and the
+	// meter's RANGE. The K3's bar is relative to a range that flips at 12 W —
+	// calibrated against a real one: 10 W showed 83 (10/12), 100 W showed 83
+	// too (100/120). The bar alone never was watts; with the PC setting to
+	// pick the range, it converts. 0 while receiving.
+	PowerW int     `json:"power_w"`
+	SWR    float64 `json:"swr"`
+	SWRRaw int     `json:"swr_raw"`
 
 	RFPower int `json:"rf_power"` // watts, the PC setting
 	AFGain  int `json:"af_gain"`  // 0-100
@@ -162,6 +168,7 @@ func (k *Kenwood) readPanel(mode string, split bool, txHz int64, txNow bool) {
 		// Cleared, not frozen: a power bar left standing after the carrier drops
 		// reads as a live transmission.
 		k.panel.PowerMeter = 0
+		k.panel.PowerW = 0
 		k.panel.SWR, k.panel.SWRRaw = 0, 0
 		k.powerPeak, k.swrPeak = meterPeak{}, meterPeak{}
 		// The S-meter only means anything while receiving.
@@ -341,6 +348,13 @@ func (k *Kenwood) readTXMeters() {
 	defer func() { k.noLatch = false }()
 	if v, ok := k.askNum("BG;", "BG", 2); ok {
 		k.panel.PowerMeter = k.powerPeak.update(kenwoodBargraphPercent(v), now)
+		if k.elecraft {
+			scale := 120
+			if k.panel.RFPower > 0 && k.panel.RFPower <= 12 {
+				scale = 12 // the K3's QRP range
+			}
+			k.panel.PowerW = k.panel.PowerMeter * scale / 100
+		}
 	}
 	// SW; — SETTLED, from Elecraft's own release note: three digits, tenths of a
 	// ratio. "SW023;" is 2.3:1, and "SW999;" is the 99.9:1 it reports instead of