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 3. GQ EMF EF Meter RF Spectrum Power Analyzer
 All in one and vertical reading
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marco

Italy
7 Posts

Posted - 04/18/2019 :  07:36:50  Show Profile  Reply with Quote
i was making a measurement on the carrier of a private radio @432 MHz. Power to the transmitter antenna = 5Watts and GQ390 placed at 1 meter distance. In vertical mode Gq390 detects the prevalent irradiated energy displaying the correct 432 MHz frequency and the relevant power density mW/m2=6000 (red beeping for alert). It also displays the integral of the power density over the whole band (.24 -->10 GHz) this one beeing higher (as it should be, i suppose, since includes also power density contributions of all the rest of the bandwidth). What i am not understanding is why the RF power density in "All in one" mode is roughly 100 times lower (mW/m2=60). Shouldn'it it be the same as the vertical mode one?

mrc
Reply #1

EmfDev

647 Posts

Posted - 04/18/2019 :  08:53:10  Show Profile  Reply with Quote
Hi marco, are you sure they are different? Did you configure the same units for both? Also maybe you need to wait maybe 3 seconds in AllInOneMode to get full reading.
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Reply #2

marco

Italy
7 Posts

Posted - 04/18/2019 :  09:25:45  Show Profile  Reply with Quote
Thanks for the quick response. I checked that the measurement unit was the same (mw/m2) and i assumed the measurement after a few seconds for both view. In spite of the same displayed unit, it seems like the effective measurement unit is not the same since there is a scale factor rather than two completely different measures....

mrc
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Reply #3

EmfDev

647 Posts

Posted - 04/18/2019 :  09:33:02  Show Profile  Reply with Quote
Is it still not the same? The AllInOne RF reading should be the same as the the .24-10GHz in the Vertical mode.
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Reply #4

marco

Italy
7 Posts

Posted - 04/18/2019 :  12:41:19  Show Profile  Reply with Quote
You mean that the readings must be the same because the only thing that change in the two views is just the "view itself" (a graphic screen representationand) not the electronic or the software elaboration of the measure?. If it is so i agree that nothing should change. Doing some more tests where an rf carrier is involved, i can see that the entity of the discrepancies is changing. For example during a umts call, depending on the distance where the measure is taken, the ratio between the two measures changes from a perfect match to a ratio of ten or more.This is not compatible with the assumption that the two measurements differs just for the graphic view itself. Sorry for disturbing on this issue but since i think that your instrument is the best on the market at this price, it would be nice to understand anything about it.

mrc
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Reply #5

EmfDev

647 Posts

Posted - 04/19/2019 :  08:50:25  Show Profile  Reply with Quote
No problem at all. The It's true that they should always have the same reading. It might be because the AllInOneMode needs to refresh the display faster that's why it needs more time to get the reading. While in Vertical RF, it only take more a little above 1 second to get full reading. That may have caused the reading difference.
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Reply #6

marco

Italy
7 Posts

Posted - 04/19/2019 :  09:28:17  Show Profile  Reply with Quote
Thanks for the answer. All the measurements have been doing were assumed true after minutes of readings, to let the system to stabilize and avoid the problem you said .....I repeated the measurements in different situations (carriers,power, distance) and most of the times the readings are differents (sometimes of order of magnitude), in particular in presence of strong carriers. Are you shure that the method of measurement is exactly the same in the two views (that is, the two reading differ just for a "view change")?. It would be useful if someone, reading this post, could make some tests to understand if this issue depends on my gq390 or is a general issue. Thanks in advance.

mrc
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Reply #7

EmfDev

647 Posts

Posted - 04/19/2019 :  09:57:48  Show Profile  Reply with Quote
The methods are different. In Vertical RF, it measures the full RF bands within 1 second. But in AllInOneMode, it does it with partitions because it needs faster time to display. That's why it needs more time for a complete measurement. I'm also testing it right now and I can get similar readings.

Maybe you can ask support@gqelectronicsllc.com if there are updates regarding this one? Thanks!
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Reply #8

marco

Italy
7 Posts

Posted - 04/23/2019 :  07:33:04  Show Profile  Reply with Quote
Thanks for the suggestion: i wrote to the support a few days ago and i am waiting for an answer. Anycase, i just wanted to add some more notes to go deeper into the issue since i think that is the core of your measurement system and has to be clarify somehow. I made some theoretical calculations and it seems to me (happy to know your opinion) that a portable 433 MHz, 5 W TX transmitter with a "short antenna" (lets suppose 60% efficiency, 0 dB gain), perfecly impedance matched, in the far field region (due to the short antenna this should be verified roughly @ distance > 2*Lambda), should have a power density of roughly 24 microwatts/cm2. I tested this assumption in free air and i found a match with calculations since in "All in one" mode the measurement are close to this value. Switching in "Vertical Mode" i found another history. The first measure (the one relevant to the detected prevalent band around 433 MHz) is 10 times greater and the integrated one (.24-->10GHz) is 100 times greater!. To be noted that measurement done in browser mode and spectrum mode are sufficiently close to the all in one mode. I thought to intermodulation third order products due to the approach to the 1 dB compression point of the receiving part of the instrument (due to the strong carrier emitted by the TX) but this should give problems if there is another tone of adequate power in the spectrum close enough to the 433 MHz to generate an 3 order intermodulation product close to the TX carrier. Watching the spectrum i can see multiple TV channels with low power (150 pw) whose potential contribution to a third order intermodulation would be negligible even with one of the two tonesat a much higher level. You mentioned you have done a test with the GQ390 in your last reply: did you tested with a carrier in similar conditions or just measuring what is in the air at you site?. If i make a measurement at my site without any exciting carrier i find no discrepancies as well.

mrc
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Reply #9

EmfDev

647 Posts

Posted - 04/23/2019 :  09:47:36  Show Profile  Reply with Quote
I was testing with an RF signal generator. So I thought everything was ok. Maybe my generator isn't as strong as the one you are using. But as I said earlier, the Vertical Mode reading should be the same or at least similar in magnitude as the AllInOneMode. Can you please email support again to ask if there's a firmware update for your 390? Thanks I'll let them know you sent an email few days ago too.
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