Spectrum graph

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rjpreston
Posts: 1
Joined: Sat Oct 12, 2019 6:06 am

Spectrum graph

Post by rjpreston »

Hi - first off, and as my first post, what a fantastic, informative and well design product this is. Well done to the creator!

A query about the spectrum graph. In a particular network environment, i have two 5GHz networks. The first on channel 100 and 80MHz wide, the second on channel 112 and 80 Mhz wide.

On the spectrum graph (see attached screenshot) these are shown as completely overlapping, whereas i would have expected them to be shown offset from each other and only partially overlapping, as (after looking up the channel frequencies) the first would presumably be transmitting centred on 5.500Ghz (5.460-5.540GHz channel width) and the second centred on 5.560GHz (5.520-5.600GHz channel width).

Is this a bug in the graph? Or have I misinterpreted the channel frequencies? quite possibly the latter due to my limited knowledge :D
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helgekeck
Site Admin
Posts: 84
Joined: Fri Sep 20, 2019 4:31 am

Re: Spectrum graph

Post by helgekeck »

hi and welcome,

i cannot tell you anything specific without haveing these two networks here to run tests on them.

please right click each of this network and save them as Raw Byte Code, send them to winfi@helge-keck.com

i will have a look

thanks
wifinigel
Posts: 6
Joined: Fri Sep 20, 2019 8:33 pm

Re: Spectrum graph

Post by wifinigel »

Hi, hope you don't mind me jumping in here, but this is not a bug in the product. Even though the networks specify different base channels (i.e. 100 & 112), for the purposes of sending 80MHz data frames, they will occupy the same group of contiguous channels.

The network on channel 100 will send its management frames (e.g. beacons) only on channel 100. However, when it needs to send 80MHz wide frames (usually data frames), it will use channels 100 - 112 (i.e. the block 100,104,108,112).

The network on channel 112 will send its management frames (e.g. beacons) only on channel 112. However, when it needs to send 80MHz wide frames, it also will use channels 100 - 112.

Even though it is possible to specify a network as being 80MHz with any 5GHz channel you choose, the actual operation of the channel at 80MHz is limited to one of a number of well-defined contiguous blocks of channels when sending data frames.

I have a cheat sheet which applies to the UK spectrum allocations on 5GHz, but other geographic areas are quite similar. If you take a look at the 80MHz allocations, you will hopefully see the contiguous blocks I am referring to and this may make a little more sense:

http://bowdennetworks.co.uk/downloads/5 ... -%20v1.pdf

Hope this helps.

Nigel.
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helgekeck
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Posts: 84
Joined: Fri Sep 20, 2019 4:31 am

Re: Spectrum graph

Post by helgekeck »

thanks nigel

will close this thread
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