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Maximum power when sweeping an antenna with an VNA?
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tszaboo:

--- Quote from: TimFox on June 23, 2022, 10:17:35 pm ---FCC Part 15 regs are rather complex, and usually refer to radiated field strength (uV/m) rather than power.
https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf
Note that the complexity is due to different limits depending on the frequency bands.

--- End quote ---
Yes, because of antenna gain. Or an internal antenna in an enclosure will behave differently, and you are only measuring the emitted power with a wide bandwidth antenna at a fixed distance. There are some practical way to measure the power output of the DUT, like replacing the antenna with a coax, but that doesn't tell the whole story.
mag_therm:
For approximate conversion of E [V/m] at distance D [m], to antenna power P [W], see
Page 29 of the FCC Part 15 doc referenced by TimFox in post #14
tautech:

--- Quote from: bayjelly on June 23, 2022, 07:38:49 pm ---Thanks a lot pdenisowski!

Seems it's overall still good to be cautious. As an extreme, I do not think the 0dBm that my VNA's tracking generator could be set to are negligible, as some folks here suggested, but maybe I'm overly cautious?
--- End quote ---
I may be being picky but when using a VNA the terminology TG is left behind where it belongs with SA's.
Yes, the modern SA/VNA use the SA mode TG port however when it's in VNA mode you should refer to it as Port 1.
This makes more sense with proper 2 and 4 port VNA's where every port is capable of providing a test stimulus.


--- Quote ---I also didn't ask for specific bands or situations because I was interested in levels that were generally considered safe. It's easier to know what to do in, say, a HAM radio band, than if the question is just "I wonder what frequencies this funky antenna I built resonates at across the entire range of my VNA".

Worse, there's also the situation where you might end up sweeping something that shouldn't be an antenna, but ends up being one.
--- End quote ---
Really, you're overthinking this.
With the plain and ordinary VNA single port sweeps of several antennas either just for learning about them or the process of tuning them, the radio a few yards away, our WiFi network and cellphones don't take a damn's worth of notice about what you're doing at typical stimulus levels you might use for this work.

Might you be exceeding local ERIP levels, possibly but as it's not normally at a fixed frequency but instead swept, any sensitive local device might only be impacted on for milliseconds at most.

Still, it's an interesting subject however if VNA's caused that much unintended mayhem in the RF spectrum they would've been banned from common use decades ago.  :horse:
pdenisowski:
Regarding units in interference hunting: most everyone uses units of dBm (although usually without specifying a bandwidth). The only people who use V/m are the cable TV folks, primarily because the FCC specifies permissible egress limits this way.

When LTE was first deployed at 700 MHz, there were a LOT of cases of cable egress causing interference in the new cellular bands, and part of the problem in getting the two sides (cellular and cable ) to work together is that they had these different ways of “measuring” interference. 

In the end, what really matters (especially to FCC) is whether it is harmful interference.  If you can show that the interference is harming your ability to use the spectrum licensed to you, then it’s an issue regardless of the absolute signal levels.  I wrote several white papers on this topic and spoke at several SCTE events to make this point.

Returning to the VNA antenna sweep question: I can’t imagine this ever meeting the definition of “harmful” interference.  I’ve seen RF interference from almost every imaginable source, but with one notable exception (on the floor of the CTIA trade show one year), I have never seen or heard of interfence being caused by test equipment.
joeqsmith:
I have some screw in Chinese imported 120V LED lights that conduct enough wide band spatter onto the house wiring that when you turn them on,  anything below about 200MHz no longer works.  All the way down to the AM radio bands.    I would imagine the house wiring makes a decent antenna and our government has yet to stop the imports.  I think your going to be fine...
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