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 3. GQ EMF EF Meter RF Spectrum Power Analyzer
 RF spectrum analyzer interference (390)
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crstory1

USA
2 Posts

Posted - 12/08/2021 :  14:13:13  Show Profile  Reply with Quote
I have detected a problem with the spectrum analyzer in the 2.4 - 2.5GHz band. If you place a 390 at about 18 inches (lambda x3) from a Dect6 DSS (spread spectrum) cordless phone base that is sweeping in the 1.92-1.93GHz band you will see a complete saturation of the analyzer on top of the 2.4-2.5GHz transceivers. The attached images demonstrate the problem with a nearby WiFi router transmitting at about 2.436GHz. This is about a half gigahertz out of bounds; I would expect far better precision even with a $125 meter. Image 1 below is the spectral response with just the WiFi on; Image 2 is the DSS sweep on top of the WiFi (which gets mulched at 2.436GHz). I cannot get the server to attach a video clip; available upon demand.




Chip Story
Reply #1

EmfDev

1645 Posts

Posted - 12/09/2021 :  10:41:57  Show Profile  Reply with Quote
Hi crstory1, have you tested the device with just the phone? or in a different place?
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crstory1

USA
2 Posts

Posted - 12/16/2021 :  17:29:02  Show Profile  Reply with Quote
Sorry for the late reply: I have tested the 390 response with and without the phone on and in different places. With the phone off, there is no DSS overprint from the 1.92 to 1.93GHz range. Image 1 shows that spectrum with just the WiFi router on (at 2.436GHz). Image 2 shows the combined response of the phone and the router. The video of this combined response demonstrates 8 separate peaks separated by about 12.5MHz sweeping the 2.4 to 2.5GHz analysis window every second. What should be 1.25MHz separation in the 1.92 to 1.93GHz DSS signal is now aliased by a factor of about 10. This interference is strongest at the near-far field response point (3x lambda) or about 18 inches with a 1.92-1.93 GHz wavelength. The DSS interference dies away from the phone, but can still be detected at about 7 feet from the base station. It is only weakly noticeable near the handset. Possible solutions... active filtering, tweak the operator length on the fft, antenna refinements ???

Chip Story
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