At what power does an antenna become dangerous?

[cybersec]

I was looking into antennas for scanning 2.4Ghz. I'm still a radio "noob", so to speak, so please excuse any dumb questions.

Previously I've used a 1000mW 9dbi antenna with my laptop to pick up WiFi, and I remember it had a fairly short reach. If I was looking to go into higher-power antennas, at what point does it become dangerous/hazardous to my health?

I'm seeing 5000mW antennas and things like that on Amazon, but are those still okay to be mounted on a vehicle or in proximity with people?

Thanks for the info guys, you're always extremely helpful.

- cybersec

 

[Markb]

If you are not planning on transmitting, you are in greater danger of the antenna falling off the mount and hitting you in the head.
The danger lies in transmitting.

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[cybersec]

If you are not planning on transmitting, you are in greater danger of the antenna falling off the mount and hitting you in the head.
The danger lies in transmitting.

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Ah okay, that makes sense. What about if you are doing transmitting?

Also, what would the point of diminishing returns be on that? I feel at some point you're getting more and more power for less and less improvement, but please correct me if I'm wrong on that.

 

[Flatliner]

I was looking into antennas for scanning 2.4Ghz. I'm still a radio "noob", so to speak, so please excuse any dumb questions.

Previously I've used a 1000mW 9dbi antenna with my laptop to pick up WiFi, and I remember it had a fairly short reach. If I was looking to go into higher-power antennas, at what point does it become dangerous/hazardous to my health?

I'm seeing 5000mW antennas and things like that on Amazon, but are those still okay to be mounted on a vehicle or in proximity with people?

Thanks for the info guys, you're always extremely helpful.

- cybersec

Firstly, a little about antennas...

1000 mW antenna is a nonsensical specification. There is no such thing. Antennas are passive devices. All they do is convert energy, not generate it. 1000 mW (1 Watt) is a figure of the power output from an amplifier. This amp will be connected to the antenna, which, in turn, converts the electricity to electromagnetic waves. It can focus the energy also (this is "gain). 1 W at 2.4 GHz can affect brain activity. Microwave ovens also TX at 2.4 GHz at around 500 W upwards.

Technically energy at that frequency is non-ionizing, (it's unlikely to cause changes to the atoms that make you), but it is borderline, and under some situations, can cause electrons to be stripped from atoms.

Your questions are not "dumb". We're glad you asked these questions. Treat RF as you would electricity.

 

[Markb]

The transmit power is different than your receiving capability. A yagi will give you very good directional reception, but you would need to insert a preamp and/or filters into your receive chain to improve your reception

I don't know at what exact output wattage it will become hazardous. That depends on where you are standing in relation to the antenna and what type of antenna it is. You are talking about 1000mW and 5000mW, which are 1 and 5 watts, respectively. That is the equivalent power output of a handheld radio.
You would have to be transmitting in the hundreds of watts to cause harm, generally speaking, but the higher the frequency, the lower the wattage needs to be in order to be hazardous, as I understand it.


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[cybersec]

Firstly, a little about antennas...

1000 mW antenna is a nonsensical specification. There is no such thing. Antennas are passive devices. All they do is convert energy, not generate it. 1000 mW (1 Watt) is a figure of the power output from an amplifier. This amp will be connected to the antenna, which, in turn, focusses the energy. 1 W at 2.4 GHz can affect brain activity. Microwave oven also TX at 2.4 GHz at around 500 W upwards.

Technically energy at the frequency is non-ionizing, (it's unlikely to cause changes to the atoms that make you), but it is borderline, and under some situation, can cause electrons to be stripped on atoms.

Your questions are not "dumb". We're glad you asked these questions. Treat RF as you would electricity.

Ahhh okay, that makes a lot more sense to me now. So antennas have no inherent danger, no matter the size or shape or dbi - all you're doing is trying to pick up as many signals as possible and receive them clearly. When transmitting though, you should be more careful when transmitting higher wattages as to not endanger those around you, but chances are nothing bad will happen at lower watts.

Without your help I probably would have been one of those idiots spending money on a 1000mW antenna when I wouldn't even need that because I'm not transmitting.

Thank you! I couldn't find any information about this stuff on Google, just annoying clickbait articles on "amplify your wifi signal with this one neat trick!!!", or "do cellphones cause CANCER? find out why your iPhone is killing you!!" so your posts are much appreciated.

 

[Flatliner]

Ahhh okay, that makes a lot more sense to me now. So antennas have no inherent danger, no matter the size or shape or dbi - all you're doing is trying to pick up as many signals as possible and receive them clearly. When transmitting though, you should be more careful when transmitting higher wattages as to not endanger those around you, but chances are nothing bad will happen at lower watts.

Without your help I probably would have been one of those idiots spending money on a 1000mW antenna when I wouldn't even need that because I'm not transmitting.

Thank you! I couldn't find any information about this stuff on Google, just annoying clickbait articles on "amplify your wifi signal with this one neat trick!!!", or "do cellphones cause CANCER? find out why your iPhone is killing you!!" so your posts are much appreciated.

You've got it.

It's all about the energy put into an antenna. And, as written by MarkB, the higher the frequency, the nastier things become, but 100 Watt into a magnetic loop at 10 MHz can stop your heart.

Also, holding an antenna in an electrical storm can lose you a few years also!

 

[cybersec]

The transmit power is different than your receiving capability. A yagi will give you very good directional reception, but you would need to insert a preamp and/or filters into your receive chain to improve your reception

I don't know at what exact output wattage it will become hazardous. That depends on where you are standing in relation to the antenna and what type of antenna it is. You are talking about 1000mW and 5000mW, which are 1 and 5 watts, respectively. That is the equivalent power output of a handheld radio.
You would have to be transmitting in the hundreds of watts to cause harm, generally speaking, but the higher the frequency, the lower the wattage needs to be in order to be hazardous, as I understand it.


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Ah okay, do you have any good links for info about preamps and filters? I tried looking around online, but apart from their Wikipedia articles, all of the information appears to be about audiophile home theatre systems haha.

And oh okay, so if I wanted to transmit at 5 watts I shouldn't be running into any issues. Thanks, you guys have answered a lot of my questions and quelled any fears I might have had haha.

 

[wyShack]

You may try your Google search again using 'RF exposure' or a similar phase. For the most part, exposure simply causes heating of the tissues (like your microwave). there are several sites on the web that go into much more detail. Amateur (HAM) radio sites like ARRL.org also have some information. Exact limits depend on frequency and what body parts are being exposed.

 

[Markb]

As far as filters and preamps go, there are a lot of good posts on this forum.

Basically, you have several types of filters. A bandpass filter for example lets a specific frequency range through to the antenna, blocking other "noise", like the FM broadcast band and pager signals which tend to overload or deafen a receiver.
The preamp must be specified for the range you want to receive as well. The amount of amplification varies with the amp, but you will ikely reach a point of diminishing returns with that.


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[Blackswan73]

You've got it.

It's all about the energy put into an antenna. And, as written by MarkB, the higher the frequency, the nastier things become, but 100 Watt into a magnetic loop at 10 MHz can stop your heart.

Also, holding an antenna in an electrical storm can lose you a few years also!

Or dropping it on a power line while installing it

 

[Flatliner]

Also, preamps need to be placed at the antenna end of coax, not the radio end.

Some filter designs can solve one problem, but cause others, as they can also generate products.

Lots to learn Mr Cybersec!

 

[Flatliner]

Or dropping it on a power line while installing it

Unfortunately you don't get the option of learning from experience with that error!

Pork scratchings, anyone?!

 

[prcguy]

The OPs original post mentions scanning 2.4GHz with a laptop and since the antenan's he's looking at are rated in power and gain, I'm thinking he may be looking at antenna/USB Wi-Fi type devices and not just antennas. If that's the case then he would be transmitting without necessarily knowing it.

5w of power from a VHF or UHF handheld into a shortened 1/4 wave whip with equal to or a little less than 0dBi gain and less than about 3in from your body is right at the OSHA limit for RF exposure for amateur operators or those people who are required to use radios and have training about RF exposure. This would be for a maximum of 6min of exposure out of every hour. For the uninformed public the RF level would be less.

1w of power into a high gain antenna at 2.4GHz would definitely be over the limit at very close range to your body and 5w into a high gain antenna would be worse.

Where does the 100w into a magnetic loop at 10MHz stopping your heart come from? I've had much much higher exposure than that and I'm still ticking. The main thing that happens is tissue heating over time and the higher the power the faster the heating.
prcguy

 

[Flatliner]

A mag loop can easily get over 4000 V at 100W. Well before it reaches that voltage at any point, the current flowing around it can be enough to becomes a effective defibrillator.

Don't try this at home.

 

[prcguy]

Mag loops are very low impedance and yes they have a lot of current in the loop. The 4,000v would obviously be at a very high impedance point but the current there would only be about .025A. 100w is still 100w.

The question is what is the field strength? I've seen many diathermy machines that will drive well over a kW into a small loop at 13MHz for localized tissue heating. I've never heard of RF specifically stopping a heart, at least not before any smoke came out.
prcguy

A mag loop can easily get over 4000 V at 100W. Well before it reaches that voltage at any point, the current flowing around it can be enough to becomes a effective defibrillator.

Don't try this at home.

 

[Flatliner]

Diathermy is a controlled procedure and relies on current flowing between two determined points. A defibrillator works in a similar way, but the application (as are freq. V & A) is different, as are the contact points. In this application, as current is passed across the chest, the heart is stopped (and will hopefully restart). 30V at 1/4A AC can do the job, though I've read figures that are considerably lower if the conditions are right - where the current travels through the body, high sodium levels, propensity to fibrillation etc

 

[Voyager]

Firstly, a little about antennas...

1000 mW antenna is a nonsensical specification. There is no such thing.

Power capability is a rating on virtually every antenna. It's not nonsense.

If you exceed the power rating, you will likely damage the antenna. Of course, this only applies to transmitting.

That said, an antenna that will only handle 1W is likely not made very well.

 

[Flatliner]

The OP's question was related to power output, rather than to power handling. Though for completeness, it is useful to mention that there is a maximum power that an antenna can transduce, though not produce.

It seems that the power output of most of the WiFi "antennas" is nonsense anyway, with one claim in the title but a lower claim in the ad. The rating isn't even based on any logic that I can tell. There used to be a lot of claims of power based on the ERP but typical eBay/Amazon sellers have little idea of what they are scribbling.

Alfa AWUS036NHV 802.11n High Power 5000mW Wireless-N USB Wi-Fi adapter w/ Rem... | eBay

 

[Voyager]

I agree he may have thought the rating was production rather than a maximum capability, but give the noob a break. My point was only that all antennas have power ratings. Not everyone knows what they mean, but they all have them.

Actually, some newer all-in-one antennas do have a power production rating, as they contain transmitters, but we are getting into left field.