MM6108 TX power (chip-level), BCF customization, and CW mode access

Hardware
1

I have already purchased ~200 MM6108 chips and built the first iteration of my prototypes with a custom FEM.

I have a few questions:

  1. TX power of the chip only:
    What is the minimum and maximum TX output power (in dBm) of the MM6108 chip itself (no FEM / no PCB gain), when using the default BCF file bcf_mf08551.bin?
    I need to drive my custom FEM at around 0 dBm input, so I want to understand if this level is achievable directly from the chip or if I need to add an external attenuator.

  2. Low power limit:
    Is it possible to configure TX power down to 0 dBm or lower via firmware/driver (e.g., via iw), or is there a hardware/firmware-enforced minimum?

  3. Custom BCF:
    What is the recommended process/toolchain to create a custom BCF file for a custom FEM (PA/LNA)?

    • Required inputs (gain tables, calibration data, etc.)

    • Any available documentation or examples

  4. CW transmit mode:
    Is there access to firmware or test mode that enables continuous wave (CW) TX for RF calibration?
    If yes, how can it be enabled?

2

Hi @AlexShmel

Out of interest, when and from where did you purchase these chips? We haven’t sold MM6108 chips directly to the public in quite some time. Support options are mentioned towards the bottom of this message.

Have a look at the MM6108 datasheet here: https://www.morsemicro.com/resources/datasheets/chips/MM6108_Data_Sheet.pdf

iw will not let you configure lower than 0dBm. There aren’t any other controls from user-space to allow you to go lower. If you do attempt this, please test it carefully - as we don’t focus on the accuracy of low power settings - you may experience some inaccuracy here.

Due to regulatory restrictions we don’t make these tools publicly available. You will need to email support@morsemicro.com and may be required to sign an NDA.

Test tools are available to anyone building a product with one of our, or our partners modules. If you have an account for our Customer Portal, please email support@morsemicro.com with the same email address you used to create that account and request access to those tools :slight_smile:

3

We purchased the hardware from Alfa Network (https://www.alfa.com.tw/), who have been our long-term partner for Wi-Fi PCBA supply and development. The order was placed a few months ago.

I’ve reviewed the MM6108 datasheet. It specifies a minimum TX power of 5.3 dBm at MCS0, but I would appreciate more detailed information across different bandwidths and MCS modes.

Our current target configuration is fixed MCS (10-0-3) and bandwidths in the 1–4 MHz range. I understand MMRC is the recommended approach, but for now we intend to proceed with fixed parameters for controlled testing.

Anyway. I plan to run a series of TX power measurements across all MCS and IW power lewels and will share results here. We have the required test equipment to do this properly.

You mentioned there are no additional controls from user space.

Is there any possibility to adjust TX power behavior from kernel space? I’ve been working with the morse_driver and could potentially explore modifications there.

Also, I noticed that in IBSS mode the driver ignores iw txpower settings and resets TX power to maximum after rescans when no connection is established. This seems like a bug i did hack around in driver to fix this.

We previously reached out to support@morsemicro.com (around 6 months ago when the project started) but did not receive a response. We will try contacting again.

We were also advised by someone on your side to obtain the necessary tools via our distributor. However, Alfa Network is not aware of these tools, so currently we are blocked.

You mentioned access is typically provided for partners using your modules.

In our case, we are not using prebuilt modules but designing hardware around the MM6108 directly. Is there a specific process or requirement to gain access to these tools in this scenario?

4

Im sorry i made a mistake regarding our chip dealler. it was V.D.Mais not Alfa network.

5

@ajudge Hi would it be possible to get reply regarding this topic ?
Also still no luck with response from support@morsemicro.com

6

@ajudge Hi is it possible to get ANY response regarding this topic ?

7

Hmm, this doesn’t sound like one of our normal distributors.

The BCF tools indicate a minimum output power of -41 dBm, but I haven’t been able to confirm that with the team yet as I’m on leave.

There is a command to set tx power. It takes an integer value representing quarters of a dBm. Check the commands header in the driver.

You’ll have to email support@morsemicro.com for access to these tools if your distributor can’t provide them. This will require an NDA. Make sure to add context to the request so you don’t get punted back here. I’ve given that team a heads up.

Because our chips are sensitive, we generally don’t support chip on board designs without additional financial commitment due to the complexities around designing and tuning. Every customer who has attempted a chip on board design in the past has had to send hardware to us for support with configuration and board/component tuning. This does not scale for us, so we work with module partners to build and distribute modules instead.

You asked earlier about the MF08551 BCF. Unless you are using an MM6108-MF08551 module, you shouldn’t use this BCF. It contains parameters to configure the FEM included on that module, and typically won’t work if you strap an alternative PA/FEM to the front of the chip.

That’s fine. The RF test tools are required by customers taking products through certification. Anyone building a product can request access to these tools. Similar process though, please contact support@morsemicro.com to request an elevation in the access privileges to your account on https://www.morsemicro.com/downloads-dashboard/

8

Hi thank you for your reply

Apologies if I pinged you too frequently during your leave.

I will wait for your response regarding the lowest TX power output of the chip.

Regarding the FEM configuration: it contains parameters to configure the FEM. I assume you do not mean that the MM6108 chip directly programs the FEM, as it should not contain any digital logic beyond TX/RX switching. I believe you are referring to the fact that the MM6108, via the BCF file, includes internal offsets for output power across different frequencies and channel bandwidths.

I have partially parsed the BCF files and observed entries such as:

[US] sig=0xd7d12398 payload_len=299 records=31
924.000 MHz bw=8 MHz [legacy_wide] power_raw=76
926.000 MHz bw=4 MHz [legacy_wide] power_raw=68
...

I assume that power_raw corresponds to quarter-dBm steps.

We initially used this particular BCF because we started developing our software stack on Heltec modules while waiting for the first revision of our own board, and it remained in use for some time. I hope to receive a response from support@morsemicro.com regarding access to the BCF editing tools. Until then, I will continue using this BCF for our custom board. Ideally, I would prefer not to fully reverse engineer the BCF format just to define correct power values.

Regarding hardware bring-up: we learned the hard way how sensitive the chip is to the VBUCK input. It took us approximately two days to bring the chip up, and another two days to achieve stable transmission. Initially, the PLL was not locking, and instead of a clean 1 MHz beacon, the device produced wideband noise around ~800 MHz at approximately -60 dBm.

After extensive troubleshooting, we replicated the resistor and capacitor network from the original Heltec module on our board, which resolved the issue. At this point, we do not require assistance with the power layout. However, if there are any known RF-related considerations that should be addressed, please let me know — we have sufficient equipment and engineering capacity to handle further optimization.

Currently, we are observing EVM at MCS0 of around 2%, which suggests that the bring-up is reasonably successful. That said, we are open to engaging with you directly for consulting or a board design review, if such support is available.

Regarding tooling: I understand that customers building products can request access. I hope to receive feedback from your support team on this.

Finally, I have one additional question about TX/RX inversion on the GPIO controlling the FEM. Based on my research, it appears that for the MM6108 this cannot be remapped or inverted without a custom BCF. However, for the MM8108 this may be configurable via the kernel driver. Could you please confirm whether this understanding is correct?

9

It was Alfa Networks i checked and rechecked with logistic a few times to confirm this.

10

Thanks for your patience with me getting back to you here my access while on leave is limited.

This is correct - but the GPIOs used on the MM6108 to control TX/RX switching is also controlled via the BCF.

Usually passives on the RF side of the chip also throw many of our customers off, in an effort to cost or size optimise. It sounds like you should be well equipped to handle this.

That’s good!
That sort of support can be organised through the support@morsemicro.com channel. Unfortunately not via this forum.

For the test tooling, I hope you do too :). There usually isn’t an issue gaining access to this.

Unfortunately the GPIOs for FEM controls are controlled by firmware and not by the Linux driver. The GPIO software referenced in the mm8108 specific code of the driver is for driving LEDs.

Back to your original question regarding minimum power. The chip itself (MM6108) can be driven to negative dBm power levels. However the variance in EVM increases below 0dBm and EVM itself continues to increase the lower you go. To achieve 0dBm at the output of the chip while using the BCF for the Heltec module, set the transmit power to 18dBm. For modules like this (using this BCF), we’ve only really tested as low as 10dBm. I can’t comment on how it would behave below this.