AVM Fritz!Box 4040 - WiFi TX power

For Developers
1

Hi, with iw list I have this data, are they real?
Above 22dBm the transmission power always seems the same.

OpenWrt 18.06-SNAPSHOT, r7106-7775802eb9
 -----------------------------------------------------
root@OpenWrt:~# iw list | grep dBm
                        * 5180 MHz [36] (23.0 dBm)
                        * 5200 MHz [40] (23.0 dBm)
                        * 5220 MHz [44] (23.0 dBm)
                        * 5240 MHz [48] (23.0 dBm)
                        * 5260 MHz [52] (23.0 dBm) (radar detection)
                        * 5280 MHz [56] (23.0 dBm) (radar detection)
                        * 5300 MHz [60] (23.0 dBm) (radar detection)
                        * 5320 MHz [64] (23.0 dBm) (radar detection)
                        * 5500 MHz [100] (23.0 dBm) (radar detection)
                        * 5520 MHz [104] (23.0 dBm) (radar detection)
                        * 5540 MHz [108] (23.0 dBm) (radar detection)
                        * 5560 MHz [112] (23.0 dBm) (radar detection)
                        * 5580 MHz [116] (23.0 dBm) (radar detection)
                        * 5600 MHz [120] (23.0 dBm) (radar detection)
                        * 5620 MHz [124] (23.0 dBm) (radar detection)
                        * 5640 MHz [128] (23.0 dBm) (radar detection)
                        * 5660 MHz [132] (23.0 dBm) (radar detection)
                        * 5680 MHz [136] (23.0 dBm) (radar detection)
                        * 5700 MHz [140] (23.0 dBm) (radar detection)
                        * 5720 MHz [144] (23.0 dBm) (radar detection)
                        * 5745 MHz [149] (30.0 dBm)
                        * 5765 MHz [153] (30.0 dBm)
                        * 5785 MHz [157] (30.0 dBm)
                        * 5805 MHz [161] (30.0 dBm)
                        * 5825 MHz [165] (30.0 dBm)
                        * 2412 MHz [1] (30.0 dBm)
                        * 2417 MHz [2] (30.0 dBm)
                        * 2422 MHz [3] (30.0 dBm)
                        * 2427 MHz [4] (30.0 dBm)
                        * 2432 MHz [5] (30.0 dBm)
                        * 2437 MHz [6] (30.0 dBm)
                        * 2442 MHz [7] (30.0 dBm)
                        * 2447 MHz [8] (30.0 dBm)
                        * 2452 MHz [9] (30.0 dBm)
                        * 2457 MHz [10] (30.0 dBm)
                        * 2462 MHz [11] (30.0 dBm)

Thanks

2

"Seems the same" -- how are you determining that? Are you running a field-strength meter?

Also, which device? AVM Fritz!Box 4040

1 Like
3

checkout "iw reg get" it tells you the maximum power limits for your country. If the values there match what you are seeing from your iw dump, then the driver does not impose any additional limits on top of that....

That said, the firmware operates on its own tx power limits. So you'll have to play with the board-2.bin if you want to change that.

Yeah, I didn't find anything useful in AVM's database. The most useful bits is this KB entry, but no technical specs of the RF-chain:

Thus, the wireless transmitter power of FRITZ! products operating in the 2.4 GHz frequency range does not exceed 100 mW / 20 dBm. When operating in the 5 GHz frequency range, it does not exceed 200 mW / 23 dBm if channels 36 to 64 (5.15 - 5.35 GHz) are used, or 1000 mW / 30 dBm when channels 100 to 140 (5.47 - 5.725 GHz) are used.

But based on the RF-Design, the limit could very well be around 22 dBm.

1 Like
4

No I'm using a software scanner and a DWA-192.
From 22 dBm to 25 should I not notice the difference?

5

iw reg get

root@OpenWrt:~# 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)

phy#1
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)

phy#0
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)

OK, thanks :wink:

6

Without a well-controlled environment and equipment designed to measure signal level (as opposed to an 802.11 client), I'd expect that real 1 dB differences are not resolvable and that 3 dB differences might be statistically significant, if averaged over a long time span.

As many 802.11 devices do their best to minimize power consumption and radiation, you'd want to make sure that all power-control features are turned off, which might be possible with hostapd, the driver itself, or not possible at all.

1 Like