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Has anyone else seen a performance difference in Upper/Lower 5GHz bands?

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Arfyness

New Around Here
... A difference in PERFORMANCE I should have said. Can't edit that now.

While I was digging for some information about whether my RT-AC68U (B2) is the identical same as RT-AC68P (which I still don't know) I stumbled down a rabbit hole leading to FCC certification documents for FCC ID MSQ-RTAC68UV2. Of course, one of these is for radio emissions as relates to human exposure. It was interesting that they tested the upper and lower 5G ranges separately... and got different measurements.

If I read it right -- and this is a giant "if" to be sure -- it looked to me that the lower band (UNII-1 / ch 36-48 / referenced as 5GHz UNII ) showed rather lower power output than the upper range (UNII-3 / ch 149-165 / referenced as 5GHz ISM).

Here's the documents page, https://fcc.io/MSQ/-RTAC68UV2
The one that got my attention is "MPE Report / RF Exposure Info" on the last page.

I'm looking at the output power (positive dBm and mW) and the Power Density. The difference is a factor of two. It also shows slight differences in antenna gain, which are opposite the power imbalance. They tested with 20MHz bandwidth.

So I wanted to know if it made a difference in my setup. I came up with the opposite to what I expected. At a set distance (one notch down on the power, same for both bands) I used the auto 20/40/80 setting, and switched the control channel between 44 and 157. It made a more significant difference than I expected. On the lower band I averaged somewhere around -55dBm to -60dBm, and for the higher band between -65dBm and -72dBm. That's enough to make the difference between stable around 500mbps and very flaky sub-200. I repeated this in a few locations several times each for a few minutes, and got consistent results.

There are a handful of other very weak networks out there, two on each part of the band, which I can occasionally see in WiFi Analyzer. But, I don't have a comprehensive site survey, so I can't rule out other interference.

If it does have anything to do with the tuning of the antennas, though, I'd be surprised if this is the only model that has some sort of fluctuation. Antenna efficiency also has a role to play in component life. (The more that goes out, the less reflects back to the components to stress them.)

I found this certainly interesting enough to share here, and searching quite a bit with all sorts of terms hasn't come up with any evidence that this is "a thing" so if you've seen it happen too, I'm interested to hear about it!

If nothing else, it's one more thing to tinker with for a little bit extra boost (or a little less tx power).

PS: Is in fact the AC68U B2 the same as AC68P? I still flipping haven't answered my original darn question!
 

Grisu

Part of the Furniture
They are mostly the same, one USB missing, 1750MHz instead of 1900 (one 2.4GHz antenna less AFAIK), different housing and antennas not screwed.
Ch. 149-165 in US have 1W while ch. 36-64 and 100-140 have only 200mW. You should see better values for upper band, maybe your testing device isnt optimized for that.
 

dlandiss

Very Senior Member
While I was digging for some information about whether my RT-AC68U (B2) is the identical same as RT-AC68P (which I still don't know) I stumbled down a rabbit hole leading to FCC certification documents for FCC ID MSQ-RTAC68UV2. Of course, one of these is for radio emissions as relates to human exposure. It was interesting that they tested the upper and lower 5G ranges separately... and got different measurements.
I have been watching that same topic in another thread. It appears that the advantage can tip either way -- perhaps depending on both the location and the Wi-Fi client hardware.

In my case there is a distinct and repeatable advantage in using the lower 5GHz band. I won't say that those who report the opposite are wrong -- just that not everyone's result is the same.
 

dlandiss

Very Senior Member
On the lower band I averaged somewhere around -55dBm to -60dBm, and for the higher band between -65dBm and -72dBm.
Does anyone know (Tim? Eric?) if the current implementation of Wi-Fi channel scanners report RSSI or RCPI? If the former, we should probably avoid adding the units "dBm" after the value, as its reference point is arbitrary.
 

dlandiss

Very Senior Member
What happened to my post??
KGB7, what did you mean by "dBa" in your missing post? That is a useful audio measurement but I can find no reference for it applicable to Wi-Fi.
 

OzarkEdge

Part of the Furniture

Arfyness

New Around Here
Does anyone know (Tim? Eric?) if the current implementation of Wi-Fi channel scanners report RSSI or RCPI? If the former, we should probably avoid adding the units "dBm" after the value, as its reference point is arbitrary.
That's a good point, I've never considered the relative nature of the scale. I've never really questioned the units shown in the app. For reference, it's the open source WiFiAnalyzer. https://play.google.com/store/apps/details?id=com.vrem.wifianalyzer

Still, whatever arbitrary point "0dBm" might be, I trust that it stays the same for all scans. (My measurements weren't meant to be absolute, it's just the relative difference I was after.)

I don't know if this answers your question, but I also had Verbose Wifi Logging turned on (in the android developer options). That puts a bit more info into the WiFi Picker, where it shows a value for RSSI which either closely or exactly matches what I see in the scanner. So if not dBm, what units would RSSI be?

Nerdy stuff like proper units really is important, so thanks for pointing this out.
 

Arfyness

New Around Here
They are mostly the same, one USB missing, 1750MHz instead of 1900 (one 2.4GHz antenna less AFAIK), different housing and antennas not screwed.
Ch. 149-165 in US have 1W while ch. 36-64 and 100-140 have only 200mW. You should see better values for upper band, maybe your testing device isnt optimized for that.
Thanks for that, I hadn't spotted the 2.4GHz difference.

My "testing device" is a Pixel 3a XL with WiFiAnalyzer (see prev. post for link). I have since considered that maybe my phone's antennae are tuned better for the low end. It could well be not that great a way to measure. It does take two ends to make a link, after all. I'll probably repeat that test with some of the other clients around the house.

Nice find. The FCC documents I found (first post) show a 1W input for the RF tests. I don't think it's mentioned in the MPE report though. That's only 3 pages, and I recall seeing it in a much longer one (and very much more confusing). I went to school for some of this stuff and it's still well sufficient to induce a headache. But still interests me quite a bit.
 

Arfyness

New Around Here
I have been watching that same topic in another thread. It appears that the advantage can tip either way -- perhaps depending on both the location and the Wi-Fi client hardware.
I've searched but didn't find another thread. I'm quite interested in reading there. Can you share a link?

In my case there is a distinct and repeatable advantage in using the lower 5GHz band. I won't say that those who report the opposite are wrong -- just that not everyone's result is the same.
Yeah it definitely depends on BOTH ends of the link, as well as site conditions. Materials reflect and absorb RF differently depending on frequency, and who knows what sorts of interference sources may be around, possibly invisible to a list of other networks.
 

thiggins

Mr. Easy
Staff member
Does anyone know (Tim? Eric?) if the current implementation of Wi-Fi channel scanners report RSSI or RCPI? If the former, we should probably avoid adding the units "dBm" after the value, as its reference point is arbitrary.
I don't know. I can check if Wireshark has a separate identifier for RCPI. Otherwise, there would be no way to know.
 

ATLga

Regular Contributor
I don't know what post you are referring to. I haven't deleted anything from this thread.
In the future use Report Post to get my attention. I don't read every thread.
Didn’t understand that either. If you look at posts numbers there isn’t one missing
 

dlandiss

Very Senior Member
Still, whatever arbitrary point "0dBm" might be, I trust that it stays the same for all scans.
"0dBm" is not an arbitrary point. That expression represents 1 milliwatt. Plus and minus values would be logarithmic ratios above or below 1 milliwatt.

That puts a bit more info into the WiFi Picker, where it shows a value for RSSI which either closely or exactly matches what I see in the scanner. So if not dBm, what units would RSSI be?
It is not dBm because the 0dB reference level is arbitrarily chosen by each manufacturer for their own devices. Since dB is a ratio measurement, and the reference point is unknown, it should be expressed merely as dB.
 

dlandiss

Very Senior Member
I don't know what post you are referring to. I haven't deleted anything from this thread.
In the future use Report Post to get my attention. I don't read every thread.
Tim, KGB7 posted a reply about 11:54CDT on 3/9/2020. It appeared in my email inbox, but not in the forum. It appears that a forum glitch dropped it into the bit bucket.
 

KGB7

Very Senior Member
... A difference in PERFORMANCE I should have said. Can't edit that now.

While I was digging for some information about whether my RT-AC68U (B2) is the identical same as RT-AC68P (which I still don't know) I stumbled down a rabbit hole leading to FCC certification documents for FCC ID MSQ-RTAC68UV2. Of course, one of these is for radio emissions as relates to human exposure. It was interesting that they tested the upper and lower 5G ranges separately... and got different measurements.

If I read it right -- and this is a giant "if" to be sure -- it looked to me that the lower band (UNII-1 / ch 36-48 / referenced as 5GHz UNII ) showed rather lower power output than the upper range (UNII-3 / ch 149-165 / referenced as 5GHz ISM).

Here's the documents page, https://fcc.io/MSQ/-RTAC68UV2
The one that got my attention is "MPE Report / RF Exposure Info" on the last page.

I'm looking at the output power (positive dBm and mW) and the Power Density. The difference is a factor of two. It also shows slight differences in antenna gain, which are opposite the power imbalance. They tested with 20MHz bandwidth.

So I wanted to know if it made a difference in my setup. I came up with the opposite to what I expected. At a set distance (one notch down on the power, same for both bands) I used the auto 20/40/80 setting, and switched the control channel between 44 and 157. It made a more significant difference than I expected. On the lower band I averaged somewhere around -55dBm to -60dBm, and for the higher band between -65dBm and -72dBm. That's enough to make the difference between stable around 500mbps and very flaky sub-200. I repeated this in a few locations several times each for a few minutes, and got consistent results.

There are a handful of other very weak networks out there, two on each part of the band, which I can occasionally see in WiFi Analyzer. But, I don't have a comprehensive site survey, so I can't rule out other interference.

If it does have anything to do with the tuning of the antennas, though, I'd be surprised if this is the only model that has some sort of fluctuation. Antenna efficiency also has a role to play in component life. (The more that goes out, the less reflects back to the components to stress them.)

I found this certainly interesting enough to share here, and searching quite a bit with all sorts of terms hasn't come up with any evidence that this is "a thing" so if you've seen it happen too, I'm interested to hear about it!

If nothing else, it's one more thing to tinker with for a little bit extra boost (or a little less tx power).

PS: Is in fact the AC68U B2 the same as AC68P? I still flipping haven't answered my original darn question!
Is there a reason you are using Auto 20/40/80 setting in the first place??

In my experience, I set it to 80mhz and forget it. It worked well for me for many years with no issues. If a device is too far away from a router, then connection speed will drop do to distance, but I don't have to worry about speed step down if a device is close to a router and I don't have to worry about router choosing speed connection based on a channel.

So why are you using Auto setting in the first place?
 
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