Question About Spectrum With Wi-Spy DBx In Very Close Proximity To AP


I was setting up a new AP and running speedtests with Chanalyzer and noticed that there were signals on other channels when testing, which were much stronger when closer to the AP. I then wondered what it looks like on the AP and saw the following when working with this AP, in this case a Netgear 1200AC (R6220) and then compared the same test with UniFi AC-Pro

Images and comparison at imgur, I tried to post them here more directly but only 1 image was allowed and I couldn’t combine them into one large image easily:

------------MODERATOR EDIT-------------- (added images):

Netgear 1200AC (R6220) -Wi-Spy Resting On AP during speedtest

Netgear 1200AC (R6220) - Wi-Spy Couple Feet Away
UniFi AC-PRO Wi-Spy On AP During Speedtest
UniFi AC-PRO Wi-Spy Couple Feet Away During Speedtest
----------END MODERATOR EDIT---------

The speedtest was done on mobile phone connected by 5Ghz on channel 36 with both APs.

My question then, is this normal to see all of that extra activity across the spectrum when measuring very close to the AP or do I have malfunctioning APs perhaps? It troubles me a bit that it’s making signal all across the DFS channels but since it’s so low power it probably does no harm I would guess.

Perhaps I’m just not understanding RF and maybe when very close to the transmitter it can seem to flood the spectrum, is that normal? Anyone with more experience I’d certainly appreciate your thoughts. Thanks!

Hi @will8741, welcome to the MetaGeek Community! Thanks for taking the time to post these images and for the great question. Sorry about the forum limitation on images. There are a couple of things going on here, and the good news is that your AP is probably working as designed.

First of all, yes, it is normal to have detectable RF activity all across the band when you are that close to a strong transmitter. The signals below -85 dBm that extend into the DFS channels, as you observed, are so low amplitude that they have attenuated into the noise floor by the time they get a few feet away from the transmitter.

Secondly, I suspect that the higher amplitude signal near channel 149 is not really there at all. That is probably an “image” of the real signal on channel 36 that is created by harmonic mixing products within the DBx itself. Those “images” typically are not visible as they are -30 dB from the true signal, but with the input signal that loud, the image is easily observed.

Thanks for the detailed response, I really appreciate it. Thanks also for adding the images to the post. I have a lot to learn about RF and this helps.

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