The Fan PWM output of the Hermes-Lite can be re-purposed to provide a DC voltage which represents the current transmission band. The output circuitry of the Fan PWM has also been re-purposed to provide a filtered DC voltage.

The output has been designed to drive the band control input of the XPA125B amplifier which has an input impedance of about 90K ohms.

Circuit

Two additional resistors have been added to the circuit and C4 has been increased in value.

BOM

Reference	Quantity	Component
Q1	1	DTC144E
Q2	1	IRLM6402
Q2 (alt)	1	PMV50UPE
R1	1	2K1 0805
R18	1	1K 0805
R19	1	5k1 0805
R20	1	511 0805
C2	1	0.1uF 0805
C4	1	10uF 1206
C5	1	0.01uF 0805

Track Mod

The original circuit layout has been utilised but one output pad needs to be cut. This can be done with a sharp blade carefully scraped across the track.

Layout

The position of C4 has moved and its original pads are now used for R20. R19 straddles the new cut track and C4 is placed across the output pads, after R19.

Connections

The pick-up point for the Band Volts PWM is on Pin 4 of DB1 and Pin 20 supplies the 3v3 which is connected to VSUP on the end plate.

Software Prerequisites

• You need an up to date Gateware on your HL2 (Band Volt Feature where added at Gateware 72p5)
• SDR Software shoud have enabled the "Dither" Feature to activate the Band Voltage output in the gateware. (in piHPSDR you will find the setting at "Menu - RX")

Voltage Output

The output voltage for a particular band is given in the following table, with the actual recorded output from the prototype:

Band	Level(mV)	Actual
1.8 MHz	230	270
3.8 MHz	460	502
5.0 MHz	690	720
7.0 MHz	920	958
10.0 MHz	1150	1183
14.0 MHz	1380	1402
18.0 MHz	1610	1620
21.0 MHz	1840	1836
24.0 MHz	2070	2048
28.0 MHz	2300	2257