Low output for Hermes Lite 2 with low VPa, VOp and VBias voltage during TX

[Cheuk-Yan Au]

Dear all,

Could you all assist with to do with low power output, it seems to be the VPa, VOp and VBias being low voltage.

Band  Measured  Reported on Thetis
10m    0.5W            1W
12m    1W               2W
15m    0.5W            1W
17m    0.6W            1W
20m    0.5W             1W
30m    0.6W             1W
40m    0.6W             1W
80m    0.5W             1W
160m   0.7W            1W

Device: Hermes lite 2 with N2ADR filter

Software: Thetis v2.10.3.8 x64 (05/11/25) (FW v7.2.8 Protocol 1) HL2 (M10BOT)

Testing: Nissei RX-503 (for PEP power)
               Digital Multimeter

               Dummy Load (100W)

               Straight Key to 3.5mm jack for testing TX on "CWU" mode.

Testing using checklist from https://github.com/softerhardware/Hermes-Lite2/wiki/No-Transmit

1. Ensure your software is configured properly for transmit. All compatible software has similar configuration.

• The PA must be enabled.Check
• Filters must be set to not attenuate your transmit signal.Check
• Software settings which may attenuate transmit per band must be adjusted to maximum.Check
• The HL2 has a 7.5dB hardware gain. This should be adjusted to maximum.Check
• Audio to the software must be configured correctly and set to the proper sampling rate (48kHz) and levels. Some software such as Quisk will not transmit if no transmit audio device is specified.Check

2. Configure your software for CW and ground the tip to shield of the front KEY/PTT stereo connector on the HL2.

• Does the HL2 switch to TX as indicated by the TX LED illuminating? PA On: Yes
• Do you hear relays changing when engaging transmit?  PA On: Yes
• Do you measure any power out on the ANT SMA connector (not the RF1 SMA connector) when terminated with a proper 50 Ohm load?  PA On: Yes (measured at dummy load)
• With the radio set in full duplex mode, do you see any RF signal (single spike) on the spectrum graph? PA On: No RF signal on Thetis spectrum graph when TX
• Do the temperature readings from the HL2 reported by software increase? What is the temperature range you see during TX?  PA On: Yes 37-> 39 holding TX for ~2sec

3. If there is no power out, check for these physical problems.

• Do you have the N2ADR board properly connect to the main HL2 board with the small 20x2 jumper board? Yes
• Confirm that the center pin of the ANT SMA connector and your external coax make proper contact. Yes
• Check that you did not damage or short any components when installing the heat shim. In particular, J31 and J32 on the bottom of the HL2 and near the heat shim have been scraped off in the past and cause TX failure. Also, B106 and L34 on the top of the HL2 near the bolt and nut hole can be damaged.No visible damage found

4. Check for expected voltages and bias current

• Configure your software for SSB and engage TX via software or external PTT. Software should report bias current in the 180-220mA range. There is no need to set your bias current as this is configured at the factory and stored in nonvolatile memory on the HL2. This YouTube video shows how to use Quisk to read (and set, which you don't need to do) the PA bias current. Other software has similar functionality. Unsure how to check, did not find meter on Thetis 2 UI.
• With TX engaged, is the DC voltage measured at Vpa 8.0V? 6.17V
• With TX engaged, is the DC voltage measured at Vop 10.15V? 6.74V
• With TX engaged, is the DC voltage measured at Vbias 10.0? 6.96V

5. Disable the PA in software and then engage CW transmit again as described in step 2. Disabled by Setup -> General -> PA Control -> PA -> Unchecked "Enabled PA" only.

• Do you measure any output when a proper 50 OHm load is connected to RF1, the low power output? PA off: PA Off: No measured voltage spike during TX  (measured at dummy load)
• With the radio set in full duplex mode, do you see any RF signal (single spike) on the spectrum graph?  PA Off: No RF signal on Thetis spectrum graph when TX
• If you have an oscilloscope, configure software to 80M and measure any RF output on DB3 pin 4 to ground and DB3 pin 3 to ground during CW transmit. What is the peak to peak voltage, and is it a clean sinusoid at the 80M frequency? DB3 is in the lower middle section of the HL2 between the AD9866 (chip which takes the smaller heat sink) and 6 blue inductors as seen in the HL2 with voltage measurement points labeled. picture. Did not measure. No oscilloscope available.

6. Check for an intermittent or poorly grounded AD9866.

• With TX engaged, apply finger pressure to the top of the AD9866 down towards the board. The AD9866 is U7 and takes the smaller heat sink as seen here. While applying pressure in various amounts and slightly different directions, does RF power out appear? No perceived change in power output
• On the bottom of the HL2 board, there is a larger hole which exposes the thermal pad of the AD9866. The thermal pad is soldered to ground at the factory and you will find it hard to notice any solder if done properly. Still, there have been cases when improving this ground solves transmit problems. Try filling this hole with solder to provide a possibly better ground to the AD9866. It will take a bit of time for the hole and surrounding ground plane to heat up enough to melt and take solder. Used continuity test to ensure that pins are connected. No visible damage found.

Best Regards,

9V1AD Chuck