Unwanted Carrier generated at central frequency in TX mode

[alessiodilibertoeng]

What type of issue is this?

permanent - occurring repeatedly

What issue are you facing?

Hi,
when I use the HackRF One in TX mode, there is always an UNWANTED CARRIER generated at the CENTRAL FREQUENCY, even if I am not generating it (e.g. SSB modes).

The issue is a lot predominant at all the HF frequencies (from 1MHz to 30-40MHz) and in conjunction with the +14dB onboard power amplifier enabled (the MGA81563 onboard). However this carrier gets lower and lower towards higher frequencies (getting bit better from around 100 MHz upwards). However the carrier still stands even at higher frequencies.

Here are the output technical data with hackrf_info command

hackrf_info version: 2023.01.1
libhackrf version: 2023.01.1 (0.8)
Found HackRF
Index: 0
Serial number: 000000000000000017c467dc331a4cc3
Board ID Number: 2 (HackRF One)
Firmware Version: 2023.01.1 (API:1.07)
Part ID Number: 0xa000cb3c 0x006a4368
Hardware Revision: older than r6
Hardware supported by installed firmware:
HackRF One

This issue is very annoying and very predominant especially when I connect a power amplifier at the HackRF output and in conjunction with the +14dB onboard power amplifier enabled (the MGA81563 onboard).

This is a big issue since I want to generated a SSB modulation but, because of this issue, there is this unwanted carrier on top of the SSB and that is a big problem in terms of modulation and more in terms of unwanted output power after a linear amplifier!

Is there any way to solve it? To what is this issue related?

Thanks in advance for you support,
Alessio

What are the steps to reproduce this?

I am using SDRangel to use HackRF One (however this issue is also present when using GNU Radio).

I enable the +14dB onboard power amplifier enabled (the MGA81563 onboard).

I simply turn TX on (the led TX turns on as well, so confirmed it is in TX mode) without any modulation, just TX on. I have tried also generating SSB transmission without any voice to modulate the signal in order to confirm that the behaviour is modulation independent.

I increase the VGA gain and I gradually see this unwanted carrier at the central frequency.

Can you provide any logs? (output, errors, etc.)

No response