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Author Topic: 5GHz channels map  (Read 1070 times)

Weaver

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5GHz channels map
« on: October 20, 2020, 02:54:49 AM »

Could anyone point me to a definitive description of which 5GHz channels are usable in the uk? And with what restrictions?

I tried channels >100 - ~140 (-ish) some time ago and if memory serves I ran into big problems which confused me into thinking that my WAP didnít support channel >100 or some reason.
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tubaman

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Re: 5GHz channels map
« Reply #1 on: October 20, 2020, 08:31:46 AM »

This is probably a good start - https://www.draytek.co.uk/support/guides/the-5ghz-wireless-band
My Google search was for "5ghz wifi uk channels".
You can certainly hit issues with the higher channel numbers as not all devices support them. Eg my Samsung TV doesn't work if I try to use Channel 100+ on my router.
 :)
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displaced

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Re: 5GHz channels map
« Reply #2 on: October 20, 2020, 08:31:51 AM »

This appears to be a definitive list, including recent additions in the top band:

https://www.silextechnology.com/unwired/changes-to-the-5ghz-wi-fi-band-in-the-uk

Unfortunately, the extra channels are DFS, and (annoyingly) Ubiquiti Networks still havenít enabled their use in the UK on their kit.

I ran with DFS channels for the best part of a year, but despite being 15 miles away from the nearest airport (LCY) I was getting weekly interruptions due to air traffic radar.  So Iíve had to stick to non-DFS channels.
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Weaver

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Re: 5GHz channels map
« Reply #3 on: October 20, 2020, 09:21:34 AM »

If you are picking up radar, would receiving it make the channel unusable for you, so it needs to be avoided?

Methinks you donít need to avoid it because you would disturb the radar, as itís too far away considering your own low tx power. It would be a sane algorithm to take you own calculated tx power at that range into account with 1/r2 or 1/r3.
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meritez

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Re: 5GHz channels map
« Reply #4 on: October 20, 2020, 09:36:22 AM »

WiFi Nigel has a whitepaper on this: http://wifinigel.blogspot.com/2018/05/updated-white-paper-on-license-exempt.html

Quote
Following the release of a Voluntary National Specification document by Ofcom in August 2017 (VNS 2030/8/3), additional channels became available for use in the UK on 5GHz.

Hope this helps
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tubaman

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Re: 5GHz channels map
« Reply #5 on: October 20, 2020, 09:40:08 AM »

If you are picking up radar, would receiving it make the channel unusable for you, so it needs to be avoided?

Methinks you donít need to avoid it because you would disturb the radar, as itís too far away considering your own low tx power. It would be a sane algorithm to take you own calculated tx power at that range into account with 1/r2 or 1/r3.

My, albeit very basic, understanding is that DFS will stop you using a channel if it detects Radar activity at that frequency. This is a legal requirement and is done automatically.
 :)
« Last Edit: October 20, 2020, 09:53:28 AM by tubaman »
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sevenlayermuddle

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Re: 5GHz channels map
« Reply #6 on: October 20, 2020, 12:47:47 PM »

Methinks you donít need to avoid it because you would disturb the radar, as itís too far away considering your own low tx power.

Not an expert.  But my own gut feeling would be that the signal generated by your WiFi would actually be a lot stronger than the true signal reflected from an object of interest to the radar operator, and a few miles (or 10s of miles)  from the radar tower?

Would be interested in the facts, if anybody has authoritative knowledge.
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Weaver

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Re: 5GHz channels map
« Reply #7 on: October 20, 2020, 09:06:46 PM »

I just assumed that radar is very very high powered, and the inverse square law is true if the beam spreads out so that means the reflection is weak but from a downrated high incident power.
« Last Edit: October 23, 2020, 04:14:44 AM by Weaver »
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sevenlayermuddle

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Re: 5GHz channels map
« Reply #8 on: October 20, 2020, 10:47:10 PM »

I have been pondering this further and have rationalised my train of thought.  My reasoning might be very deeply flawed, but is as follows...

1.  If I were to hold a signal strength meter within an inch of my WiFi APís Antenna, it would read quite a high signal. The radiated signal is tiny on the grand scale of things but at a one inch distance, inverse square law acts in my favour.

2.  If I were to hold the same meter in fresh air, a few miles from a massively powerful transmitter, it would read less high than in (1), because inverse square law would massively diminish the signal strength.

3. If I were then to measure the reflected signal from a surface positioned as in (2), the reflected signal is likely to be very much weaker again than the original signal seen by the meter.  This makes me think that the desired reflected signal seem by the radar tower would be much weaker than the unwanted direct signal from my WiFi, tiny as it is.

I therefor conclude that the signal from my WiFi would strongly ďdazzleĒ the radar tower, swamping the desired reflected signals.

But I may be wrong, maybe spectacularly so.   I vaguely recall we have at least one radio Ham among our members?    Donít recall who that is but if he sees this thread, his contribution might be interesting... :)
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Weaver

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Re: 5GHz channels map
« Reply #9 on: October 20, 2020, 11:10:27 PM »

Magnetic fields donít follow 1/r2 but 1/r3, because magnetic detection is differential, so things depend on which mode the detection is in - based on E field or B field. A point source is supposed to be like 1/r2 in terms of energy spread but a dipole with a cylindrical distribution would be 1/r. A beam-type rotating parabolic tx radar dish might do better than 1/r2 in terms of long range. This is all me just guessing though, so I should just shut up.  ;) :-X ??? The reflected wave will possibly have a different dependence on distance compared with the original tx wave too, to complicate things even more.
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Alex Atkin UK

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Re: 5GHz channels map
« Reply #10 on: October 21, 2020, 03:01:29 AM »

This appears to be a definitive list, including recent additions in the top band:

https://www.silextechnology.com/unwired/changes-to-the-5ghz-wi-fi-band-in-the-uk

Unfortunately, the extra channels are DFS, and (annoyingly) Ubiquiti Networks still havenít enabled their use in the UK on their kit.

I ran with DFS channels for the best part of a year, but despite being 15 miles away from the nearest airport (LCY) I was getting weekly interruptions due to air traffic radar.  So Iíve had to stick to non-DFS channels.

Ubiquiti have had issues with false positive DFS hits and I believe their new APs often have it enabled at a later date.  But things like the NanoHD do work with DFS channels now.

My own network is actually on channel 100 with 160Mhz channel width.
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Weaver

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Re: 5GHz channels map
« Reply #11 on: October 21, 2020, 03:40:35 AM »

Alex, do you have an initial delay before your DFS allows the WLAN to work ?
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psychopomp1

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Re: 5GHz channels map
« Reply #12 on: October 21, 2020, 04:42:04 PM »

It usually takes 2-3 mins for the DFS channels to become active once you select a DFS channel. I guess this is the time it takes for the router to detect any channel conflicts.
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Alex Atkin UK

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Re: 5GHz channels map
« Reply #13 on: October 21, 2020, 04:44:56 PM »

Alex, do you have an initial delay before your DFS allows the WLAN to work ?

Yes, I think it can take up to 10 minutes.  But this equally applies to every router/AP I've ever used on 5Ghz that is based on OpenWRT.
« Last Edit: October 21, 2020, 07:18:57 PM by Alex Atkin UK »
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j0hn

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Re: 5GHz channels map
« Reply #14 on: October 21, 2020, 05:52:45 PM »

My Asus RT-AC68U takes about 3 mins for 5GHz to become available when i boot/reboot the router. I use DFS channel 100.
If I'm using a non DFS channel it takes just under 2 mins to boot

The 2.4GHz radio only takes about a minute to boot up.
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