I’ve some spare 10dbi antennas, can I use those on my hap ax3? is there anything I need to do/check/know before changing it, I got afraid by the stickers that came with it when I bought it, hence the question.
Big respect,
Waldecir
The stickers should be warning to not power the radios without antennas connected.
Suitable antennas can be used alright as well as dummy loads (if you are not using wi-fi, as a better be safe than sorry measure if the radio are turned on accidentally).
The final amplifier “expects” a load (impedance, standard antennas have 50 Ohms) if there isn’t one the power emitted may “remain” in the IC and overheat it.
http://forum.mikrotik.com/t/hap-ax3/168940/1
http://forum.mikrotik.com/t/solved-is-it-mandatory-to-mount-antennas-on-hap-ac3/172910/1
Got it, I’ve spare antennas like this one https://www.amazon.com/Superbat-Antenna-Connector-Network-Wireless/dp/B08X4DYQK7/ but I cannot find the ohms specifications for it
fix: It does say Impedance 50 Ohm so I should be able to use it, thank you.
You should specify the antenna gain to comply with regulations. But to be honest, I wouldn’t be to worried about the default antennas…unless you have some sort of problem?
I wouldn’t be preoccupied of emitting too much signal, the stated range on the Amazon page is:
Maximum Range 7.7 Inches
that would be what, -117dB? 
The linked to antenna is declared as 8 db gain, this (seemingly identical) one:
https://www.amazon.com/Repeater-Wireless-Security-Surveillance-RT-AC68u/dp/B08RHKTZ9X
has no stated Range but is declared as 10 dB gain.
Seems like that changing it helped it went from 400Mbits to ~720Mbits if I’m close to the router, but I’m going to do more tests.
Yep, the factory ones should be 5.5dB, so 8 or 10 is anyway a big improvement (though you should make sure you are not going above allowed emissions by your local norms).
Since the transmission is two-way, when you use a high gain antenna you might be able to actually lower emissions below the max allowed and still have better connection.
Okay now you have me thinking perhaps repace my AX3s with these bad boys.
https://www.amazon.ca/Portable-Antenna-Dual-Band-Omnidirectional-Router/dp/B08LZHV83P/ref=sr_1_7?crid=2LK4POLSJPVAY&dib=eyJ2IjoiMSJ9.d7o75FpnshnrVKGe5-c-B68HFFzp0iKhzPKsakuKGUIZn-erRPTYVZjKSuecgvF_aAxk649CL4RzmR20jM6Qn8jXNRNWmSOF2ikrxrDmMF338-LxXo96hukArnnarxzimVEfV129C1Fm3btJAEJkhm2WHB4wF6aBF52e2PPHOE7Sp1R8BBy2v7NAMbqoKEjjjIL1_yr8ZDEOfJ0UWjtyu1aVy85RD4ECDZaAyvBI6bcrZLR0_H-ZaZGBERvnR33aVVruZKbA8e-ZifNzneZBMxgNh26WFwdmTWdzx788vIY.KEwml83_cv5vqEeCOhOMusSnfRCOWBlH6PNzbvLEk70&dib_tag=se&keywords=wifi+antennas+12dbi&qid=1710527626&sprefix=wifi+antennas+12dbi%2Caps%2C72&sr=8-7
You can also get the 12 dB version of the same model as the OP on aliexpress:
https://www.aliexpress.us/item/2251832727365570.html
dB’s are thrown around like they were peanuts, no wait, maybe there are different definitions of dB 
…
I would really like to see these actually tested and rated according to “our” dB’s.