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bigbillsd
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Metal AC transmit power setting?

Fri Jun 14, 2019 6:05 pm

I'm not a radio geek but I understand there will usually be a setting to change the transmitter power so as not to overwhelm a close device and subsequently will help reach further away devices by setting it higher. I don't see that on my Metal AC device. I do see a "gain" setting. Is that something I would change to look at very close hotspots vs AP's at a distance? Again, I am not a radio geek, just an IT geek.

Is there a transmitter power setting in the WebFig or?

An omni directional antenna came with the device that I think it said it was 8 db. Should i always keep that number in the "gain" field or do I adjust that for distance to an AP? I wonder if khanacadamy.com has a radio lesson..

Thanks for any clarification with tuning the radio side of this device.

-Bill

PS. I have this mounted on my RV and using it in CPE mode. Sometimes the only Internet available is from one of my cellular Hotspots, and other times there is a AP i can use either close or in a short distance. I read the manual but its not very helpful in this regard.
 
mkx
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Re: Metal AC transmit power setting?

Fri Jun 14, 2019 6:41 pm

Indeed there is no direct way of setting Tx power of wifi radios on Mikrotik devices. Instead there's antenna gain setting (which you already found), which can be used for what you want to achieve.

The idea is this: there are legal limits about effective radiated power of wifi devices (EIRP), let's assume it is 20 dBm (can be more in some countries in some part of spectrum). EIRP equals Tx power of radio less loss in cables (if any) plus antenna gain. Routeros will limit Tx power if antenna gain is high. So yes, you can set antenna gain to 0 (or whatever minimum value on the particular device) when you want high Tx power and set antenna gain to some bigger number (e.g. 10) when you want to reduce Tx power.
For sure there's Tx amplifier max power, which is usually between 20 and 30 dBm depending on device type and transmission mode.

When determining the right Tx power you should assess signal level at your typical device position. It seems that most devices work best when signal level is between -50 dBm and -70 dBm (less negative number means better signal). If signal is stronger, devices experience "artificial" noise (caused by their Rx pre-amplifier). If the signal is weaker, more robust (and slower) transmission modes are used.
BR,
Metod
 
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bigbillsd
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Re: Metal AC transmit power setting?

Fri Jun 14, 2019 11:57 pm

Thank You! I was guessing wrong about the gain numbers. I was thinking higher was stronger. Thanks again for the info. -Bill
 
mkx
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Re: Metal AC transmit power setting?

Sat Jun 15, 2019 10:11 am

I was guessing wrong about the gain numbers. I was thinking higher was stronger.
You were thinking right. What puzzles here is the way that antenna gain is used in ROS. By changing the setting actual antenna gain is not changed, because antenna gain is physical property of anantenna (array) - exception here are phase array antennae where antenna characteristics (incuding gain) can be adjusted. Instead, as I explained, the Tx power gets adjusted to keep radiated power within limits
BR,
Metod

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