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grzaks
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Laptop next to RB912UAG has -50dBm WiFI signal strength. Why?

Fri Aug 05, 2022 2:25 pm

I'm not experienced in radio/antenna/wireless physics. Could somebody please take a look at the attached photo of my RB912UAG setup and tell me if I do something wrong (my guess is WiFi antennas in dumb positions?).
The setup is: The ppp-client configuration is as follows:
[admin@RB-dsg-HCG081AERV3-B] /interface/wireless> print detail
Flags: X - disabled; R - running
 0  R name="wlan1" mtu=1500 l2mtu=1600 mac-address=18:FD:74:0B:E0:50 arp=enabled interface-type=Atheros AR9300 mode=ap-bridge ssid="Routerboard" frequency=auto band=2ghz-b/g/n channel-width=20/40mhz-XX secondary-frequency=""
      scan-list=default wireless-protocol=802.11 vlan-mode=no-tag vlan-id=1 wds-mode=disabled wds-default-bridge=none wds-ignore-ssid=no bridge-mode=enabled default-authentication=yes default-forwarding=yes default-ap-tx-limit=0
      default-client-tx-limit=0 hide-ssid=no security-profile=default compression=no


The issue is that IMHO the WiFi signal is very week. The laptop standing right next to it has -40-50 dBm signal strength displayed on the registration table:
[admin@RB-dsg-HCG081AERV3-B] /interface/wireless/registration-table> print
Columns: INTERFACE, MAC-ADDRESS, AP, SIGNAL-STRENGTH, TX-RATE, UPTIME
#  INTERFACE  MAC-ADDRESS        AP  SIGNAL-STRENGTH  TX-RATE               UPTIME
0  wlan1      DC:53:60:8A:5A:39  no  -48dBm@HT40-4    150Mbps-40MHz/1S/SGI  1h26m50s


The very same laptop connected to the other device: Mikrotik LtAP Mini (with small built-in antennas) standing on the very same desk has much better signal:
[admin@dsg-EB820F7A171A-B] /interface/wireless/registration-table> print
Columns: INTERFACE, MAC-ADDRESS, AP, SIGNAL-STRENGTH, TX-RATE, UPTIME
#  INTERFACE  MAC-ADDRESS        AP  SIGNAL-STRENGTH  TX-RATE  UPTIME
0  wlan1      DC:53:60:8A:5A:39  no  -35dBm@1Mbps     1Mbps    2m59s


What is the reason for that? How can I improve the signal strenght in routerboard device?


IMG_20220805_125241.jpg
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krafg
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Re: Laptop next to RB912UAG has -50dBm WiFI signal strength. Why?

Fri Aug 05, 2022 10:25 pm

Internal LtAP Wi-Fi antenna is solded. Remember that each connector you your cable have attenuation on your signal strength.

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grzaks
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Re: Laptop next to RB912UAG has -50dBm WiFI signal strength. Why?

Mon Aug 08, 2022 1:18 pm

Remember that each connector you your cable have attenuation on your signal strength.
I'm aware of that. Unfortunatelly there is no other way with external antennas than through connectors. At least MMCX is one and SMA on the other end of the cable is another. Connectors make the signal strength weaker but the antenna itself should be much stronger. Right? Otherwise using external antennas would make no sense
 
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bpwl
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Re: Laptop next to RB912UAG has -50dBm WiFI signal strength. Why?

Tue Aug 09, 2022 11:23 am

A 2 dBi antenna is not strong at all. It is just a little bit stronger than the simplest short di-pole (which is at 1.5dBi). Difficult to have less gain.

-50dBm ... is 70dB loss ..... due to the receive antenna coverage of only a very small part of the surface of the sphere representing the omnidirectional (+20dBm) transmitted power.
Very close to the antenna (eg smartphone standing against the hAP ac2 housing), can give -10dBm received signal. (This is 20dBm too much for good reception, -35dBm is considered the max allowed for received signal, -86dBm is mostly the minimum). Signal drops 6dB with each doubling of the distance (in free field condition).
 
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mkx
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Re: Laptop next to RB912UAG has -50dBm WiFI signal strength. Why?

Wed Aug 10, 2022 12:48 am

Difficult to have less gain.

There's surprisingly large number of antennae types out there with gain lower than 0 dBi ... mostly they're multi-band antennae and most of them are shitty only at lower part of "covered" frequency band, but vast majority of specs hide this "minor detail" ... which can make life of some users really miserable.

But as mentioned: even with perfect antennae higher gain comes with a price: non-spherical gain diagram. Which means better performance in certain direction(s) and (much) worse performance in all other directions.

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