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How can I override the wlan driver's region limitations to permit the (legal) 900MHz unlicensed operation of my 802.11ah evaluation kit?

The [Silex evaluation kit for 802.11ah][1] doesn't seem to work at sub-GHz. A spectrum analyzer shows no power in the sub-GHz. It is operating, apparently, at 5.825GHz. Their support email has failed to respond after 11 days and this appears to be a problem with the SSD that comes with the kit as evidenced by the following output.

pi@raspberrypi:~ $ iwconfig wlan0
wlan0     IEEE 802.11  ESSID:"Wi-Fi"  
          Mode:Managed  Frequency:5.825 GHz  Access Point: 84:25:3F:87:FA:E8  
          Bit Rate=6 Mb/s   Tx-Power=30 dBm  
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=70/70  Signal level=-32 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:100   Missed beacon:0

pi@raspberrypi:~ $ cat ~/sx-newah/conf/US/sta_halow_sae.conf
ctrl_interface=/var/run/wpa_supplicant

country=US
network={
    ssid="Wi-Fi"
    proto=RSN
    key_mgmt=SAE
    ieee80211w=2
    pairwise=CCMP
    group=CCMP
    sae_password="12345678"
    freq_list=2422 2432 2442 2452 2462 5180 5185 5190 5195 5200 5205 5210 5215 5220 5225 5230 5235 5240 5745 5750 5755 5760 5500 5520 2437 2457 5765 5770 5775 5780 5785 5790 5795 5800 5805 5810 5815 5820 5825
    scan_freq=2422 2432 2442 2452 2462 5180 5185 5190 5195 5200 5205 5210 5215 5220 5225 5230 5235 5240 5745 5750 5755 5760 5500 5520 2437 2457 5765 5770 5775 5780 5785 5790 5795 5800 5805 5810 5815 5820 5825
}
p2p_disabled=1
ignore_old_scan_res=1

pi@raspberrypi:~ $ iw reg get
global
country US: DFS-FCC
(2402 - 2472 @ 40), (N/A, 30), (N/A)
(5170 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
(5250 - 5330 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
(5490 - 5730 @ 160), (N/A, 23), (0 ms), DFS
(5735 - 5835 @ 80), (N/A, 30), (N/A)
(57240 - 63720 @ 2160), (N/A, 40), (N/A)

PS: I've tried modifying the conf files.
[1]: https://www.silextechnology.com/connectivity-solutions/embedded-wireless/sx-newah-evaluation

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  • Is wlan0 really that board? Isn't it the built-in Raspberry Pi Wi-Fi interface instead? Are there other visible interfaces? Is there anything in the output of dmesg that would point out to the board actually being recognised? Is there a driver loaded? Isn't that board supposed to only support sub-1 GHz? – jcaron Sep 29 '20 at 17:13
  • It is really that board. I have 2 systems and can ping between them with one configured as an AP and the other as a STA. And, yes, it is supposed to support sub-1GHz... 900MHz unlicensed band. That is, in fact, what this question is about. – James Bowery Sep 29 '20 at 20:49
  • From what little public information is available from Silex, their 802.11ah module is supposed to support only sub-1 GHz. The block diagram shows an NRC7292 and an RFFM6901, which only support sub-GHz. Do the on-request docs say otherwise? If they don't, the fact that it's showing 5.8 GHz points to something wrong. Either you're not talking to the right interface, or they didn't ship the right board, or the specs are completely off... Try to find something in your dmesg output which would point to the actual chip/driver. – jcaron Sep 29 '20 at 21:20
  • My mistake. It is, indeed, operating in the 900MHz spectrum. What threw me off was the combination of iwconfig's output, the "freq_list" in the configuration that didn't include 900MHz spectrum AND the fact that prior to taking delivery of the spectrum analyzer, I had modified the "freq_list" (and scan_freq) to be the 4 900MHz frequencies with the highest bandwidth. This caused the AP/STA link to fail which meant nothing appeared in the 900MHz spectrum when I ran the frequency analyzer. I reverted configuration and 928MHz shows up. Deleting the question. – James Bowery Sep 30 '20 at 0:38
  • 1
    Hey instead of deleting the question, the best would be to edit the answer out of your question and post it as an answer. That way, future users who have made the same mistake will have helpful guidance. Thanks! – anonymous2 Sep 30 '20 at 12:32
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Partially my mistake. It is, indeed, operating in the 900MHz spectrum.

What threw me off was the agreement between all of the command outputs provided in the question, that there was no support for 900MHz, in combination with a mistake of my own:

I modified the "freq_list" (and scan_freq) to include the 900MHz frequencies. This caused the driver to fail to broadcast at all. I didn't realize this, so upon taking delivery of the spectrum analyzer nothing was showing up in 900MHz thereby "confirming" my belief the unit was operating at 5GHz (the spectrum analyzer I bought only went up to the 2.4GHz range). Only after realizing that the radio might not be broadcasting at all did I revert the configuration to the original. At that point the spectrum analyzer showed 928MHz power.

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