7 ms·

>How did this thing get FCC approval? Looking at the radio display, it seems like the peak power is about 7-8 S-units. At VHF, that would be about -100dBm; or

>How did this thing get FCC approval? Looking at the radio display, it seems like the peak power is about 7-8 S-units. At VHF, that would be about -100dBm; or about 100 femto-watts. I presume that the charger is pretty near the radio. With free-space path loss being inverse square law, it's essentially going to be completely negligible within a very short distance. Oh, and if the antenna is indeed near the charger (say within one wavelength, 2 meters in this case) it might be inside the near-field - which means that you're getting additional power transferred that wouldn't be reaching the far-field, and you might even be affecting the behavior of the device due to coupling. Looking at the FCC report, the radiated emissions are totally in-line with FCC Class B requirements. Modern ham radio equipment has exquisitely sensitive receivers and you easily hear all kinds of interference from digital devices that are completely Part 15 compliant. The prevalence of switched mode power supplies literally everywhere has made HF radio completely unusable for many people outside rural areas.

crote 3y ago
Do you have any idea how that power compares to regular FM radio broadcasts, which are somewhat close in frequency? Is this something a regular radio would detect, or is OP just trying to listen to a handheld radio half a continent away using a really sensitive receiver with the volume knob turned all the way up?
- NovemberWhiskey 3y ago
  To get a very broad idea: if you had perfectly efficient but isotropic antennas (you don't) this would be about the power level you'd get receiving a typical 3W hand-held radio signal at 140MHz from 1,000 kilometers away. This is why you can talk to the International Space Station easily enough with vanilla ham radio equipment. Or, taking a notoriously powerful FM radio station like KRUZ 103.3, it would be like hearing that station from perhaps 300,000 kilometers away. Most loss is not free-space loss though - it's due to reflections from man made objects and absorption into the earth that results in line-of-sight effects at these frequencies.
  - amatecha 3y ago
    How did you come to that estimation? The strength of the RFI on the waterfall suggests received signal strength comparable to someone transmitting on a 5w HT within, say, 5-10 miles (aka not in the immediate neighbourhood, but pretty nearby). Someone transmitting 3w at 1000km distance will not register even the slightest on any amateur receiver, even with RF gain absolutely cranked to the max and with a massive antenna.
    - NovemberWhiskey 3y ago
      I actually updated my post about the same time you wrote this response; I was just considering free-space path loss, which is not where most of the loss is in typical ham scenarios. Most of the 5W in the case you described is getting lost in a terrible compromise antenna, then due to line of sight effects (assuming that the user is not standing on a hill or something) and multipath.
  - TylerE 3y ago
    The ISS also orbits quite low. If you're relatively close to the path it's only a few hundred miles away. Small temporal window due to the speed, but still.
- amatecha 3y ago
  Due to proximity, the interference from the charger is comparable to what the receiver was expecting from a normal signal (like an amateur radio repeater or fellow operator's station), which is why his radio broke squelch while scanning. Because the radio is relatively close to the charger, the RFI is picked up quite well. Comparing to a broadcast FM station, the strength of the RFI as observed by any nearby radio will be trivial by comparison. Broadcast stations are some of the highest-power radio transmissions around us, typically thousands of kilowatts (for example the rock station near me transmits at an ERP of 51,000 watts[0]). You will hear this station clearly no matter what kind of nearby RFI is present, and the receiver's AGC will reduce RF gain to probably as low as it goes. By comparison, amateur radios typically operate in the range of 5-100 watts. Thus you might gather that comparing localized RFI to broadcast stations is not a meaningful comparison. [0]https://en.wikipedia.org/wiki/CFOX-FM https://en.wikipedia.org/wiki/CFOX-FM
  - FireBeyond 3y ago
    > Broadcast stations are some of the highest-power radio transmissions around us, typically thousands of kilowatts (for example the rock station near me transmits at an ERP of 51,000 watts[0]). I don't think so. Not "thousands of killowatts" transmitted. Your example is as you say, an ERP of 51kW. But even ERP doesn't refer to the transmitter. An ERP of 51,000W is most likely a 5-10kW transmitter, with a gain factor of 5-10.
    - TylerE 3y ago
      Back in the pirate radio days 100 and 250kw transmitters were common. Back in the '30s a few AM stations ran at 500kw, and could be picked up on other continents.
      - FireBeyond 3y ago
        AM? Definitely, but even that is 100, 250, 500. Not "thousands of kW".
    - amatecha 3y ago
amatecha 3y ago
I use HF radio all the time from inside my home, in the middle of one of the densest cities in BC. Within the past few weeks I've made contacts with stations in Alaska, Belize, Costa Rica, Colombia, Russia and Japan with a radio inside my home in Vancouver, Canada. HF is 10000% usable in urban areas. It's not optimal or perfect, but it's just fine.
- NovemberWhiskey 3y ago
  Sure. Right now, we're coming towards the top of a sunspot cycle that results in SFI levels not seen in 20 years. Let me know how you were doing in 2019. There's obviously a seasonal overlay here.
  - jrockway 3y ago
    Oh man, I haven't been paying attention to the sunspot cycle. I got my license at a low and committed to being depressed about it forever, but ... time fixes everything I guess!
  - amatecha 3y ago
    I wasn't an op in 2019 -- got my certification in 2022. That said, I used to receive FT8 with my RTL-SDR and have a few screenshots. Here's a map of my received signals on 40m, overnight in May 2020, with a random-wire antenna: https://i.imgur.com/flfyIZx.png https://i.imgur.com/flfyIZx.png At that time I lived in an even more densely-populated area (a condo complex with over 100 units, on a main street, surrounded by other similarly-large condo complexes).
  - threeio 3y ago
    its still doable in 2019... just not as plentiful ;) I was still able to get DXCC during the lows in a Silicon Valley downtown tiny lot (however, this isn't an apartment in a major city)
- jrockway 3y ago
  Making the contact is easy (the interference you hear doesn't exist at the receiver), hearing the other end is hard. Most of my indoor QSOs are people running 1500W FT8 which is ... an unnecessary amount of power. (Meanwhile, I'm sitting here transmitting at 3W.) I often look at the automated reports and look sadly at the 99% of stations that can hear me but that I can't hear.
t0mas88 3y ago
Near-field being as big as 2 meters from the charger can be quite relevant for use in aircraft. Since on a narrow-body aircraft passengers can easily be within 2 meters of some of the VHF antennae. On the other hand, aviation voice radios aren't very sensitive and navigation radios have filtering built-in. So the output of an Apple charger is probably some orders of magnitude too small to cause any issues.
- jrockway 3y ago
  > Since on a narrow-body aircraft passengers can easily be within 2 meters of some of the VHF antennae. But, separated by a very large piece of conductive metal. (I think even carbon fiber planes have a conductive layer in there, to prevent damage from lightning strikes.)
  - skykooler 3y ago
    Isn’t carbon fiber conductive itself?
    - tonyarkles 3y ago
      Carbon fibre is definitely conductive. A couple of years ago I measured a 1” diameter tube and got about 15ohms/ft.
      - Animats 3y ago
        Right, it's a resistor. This is a problem for airframes and wind turbine blades. Its resistance is too high to deal well with lightning. So aluminum is needed to provide a conductive path.
    - thenickdude 3y ago
      Yes, and blocks radio transmissions very nicely. When making a model airplane with a carbon fibre hull, we have to add a plain fibreglass or plastic window for the antenna to receive through.
PM_me_your_math 3y ago
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crote 3y ago

Do you have any idea how that power compares to regular FM radio broadcasts, which are somewhat close in frequency? Is this something a regular radio would detect, or is OP just trying to listen to a handheld radio half a continent away using a really sensitive receiver with the volume knob turned all the way up?

NovemberWhiskey 3y ago
To get a very broad idea: if you had perfectly efficient but isotropic antennas (you don't) this would be about the power level you'd get receiving a typical 3W hand-held radio signal at 140MHz from 1,000 kilometers away. This is why you can talk to the International Space Station easily enough with vanilla ham radio equipment. Or, taking a notoriously powerful FM radio station like KRUZ 103.3, it would be like hearing that station from perhaps 300,000 kilometers away. Most loss is not free-space loss though - it's due to reflections from man made objects and absorption into the earth that results in line-of-sight effects at these frequencies.
- amatecha 3y ago
  How did you come to that estimation? The strength of the RFI on the waterfall suggests received signal strength comparable to someone transmitting on a 5w HT within, say, 5-10 miles (aka not in the immediate neighbourhood, but pretty nearby). Someone transmitting 3w at 1000km distance will not register even the slightest on any amateur receiver, even with RF gain absolutely cranked to the max and with a massive antenna.
  - NovemberWhiskey 3y ago
    I actually updated my post about the same time you wrote this response; I was just considering free-space path loss, which is not where most of the loss is in typical ham scenarios. Most of the 5W in the case you described is getting lost in a terrible compromise antenna, then due to line of sight effects (assuming that the user is not standing on a hill or something) and multipath.
- TylerE 3y ago
  The ISS also orbits quite low. If you're relatively close to the path it's only a few hundred miles away. Small temporal window due to the speed, but still.
amatecha 3y ago
Due to proximity, the interference from the charger is comparable to what the receiver was expecting from a normal signal (like an amateur radio repeater or fellow operator's station), which is why his radio broke squelch while scanning. Because the radio is relatively close to the charger, the RFI is picked up quite well. Comparing to a broadcast FM station, the strength of the RFI as observed by any nearby radio will be trivial by comparison. Broadcast stations are some of the highest-power radio transmissions around us, typically thousands of kilowatts (for example the rock station near me transmits at an ERP of 51,000 watts[0]). You will hear this station clearly no matter what kind of nearby RFI is present, and the receiver's AGC will reduce RF gain to probably as low as it goes. By comparison, amateur radios typically operate in the range of 5-100 watts. Thus you might gather that comparing localized RFI to broadcast stations is not a meaningful comparison. [0]https://en.wikipedia.org/wiki/CFOX-FM https://en.wikipedia.org/wiki/CFOX-FM
- FireBeyond 3y ago
  > Broadcast stations are some of the highest-power radio transmissions around us, typically thousands of kilowatts (for example the rock station near me transmits at an ERP of 51,000 watts[0]). I don't think so. Not "thousands of killowatts" transmitted. Your example is as you say, an ERP of 51kW. But even ERP doesn't refer to the transmitter. An ERP of 51,000W is most likely a 5-10kW transmitter, with a gain factor of 5-10.
  - TylerE 3y ago
    Back in the pirate radio days 100 and 250kw transmitters were common. Back in the '30s a few AM stations ran at 500kw, and could be picked up on other continents.
    - FireBeyond 3y ago
      AM? Definitely, but even that is 100, 250, 500. Not "thousands of kW".
  - amatecha 3y ago

amatecha 3y ago

I use HF radio all the time from inside my home, in the middle of one of the densest cities in BC. Within the past few weeks I've made contacts with stations in Alaska, Belize, Costa Rica, Colombia, Russia and Japan with a radio inside my home in Vancouver, Canada. HF is 10000% usable in urban areas. It's not optimal or perfect, but it's just fine.

NovemberWhiskey 3y ago
Sure. Right now, we're coming towards the top of a sunspot cycle that results in SFI levels not seen in 20 years. Let me know how you were doing in 2019. There's obviously a seasonal overlay here.
- jrockway 3y ago
  Oh man, I haven't been paying attention to the sunspot cycle. I got my license at a low and committed to being depressed about it forever, but ... time fixes everything I guess!
- amatecha 3y ago
  I wasn't an op in 2019 -- got my certification in 2022. That said, I used to receive FT8 with my RTL-SDR and have a few screenshots. Here's a map of my received signals on 40m, overnight in May 2020, with a random-wire antenna: https://i.imgur.com/flfyIZx.png https://i.imgur.com/flfyIZx.png At that time I lived in an even more densely-populated area (a condo complex with over 100 units, on a main street, surrounded by other similarly-large condo complexes).
- threeio 3y ago
  its still doable in 2019... just not as plentiful ;) I was still able to get DXCC during the lows in a Silicon Valley downtown tiny lot (however, this isn't an apartment in a major city)
jrockway 3y ago
Making the contact is easy (the interference you hear doesn't exist at the receiver), hearing the other end is hard. Most of my indoor QSOs are people running 1500W FT8 which is ... an unnecessary amount of power. (Meanwhile, I'm sitting here transmitting at 3W.) I often look at the automated reports and look sadly at the 99% of stations that can hear me but that I can't hear.

t0mas88 3y ago

Near-field being as big as 2 meters from the charger can be quite relevant for use in aircraft. Since on a narrow-body aircraft passengers can easily be within 2 meters of some of the VHF antennae. On the other hand, aviation voice radios aren't very sensitive and navigation radios have filtering built-in. So the output of an Apple charger is probably some orders of magnitude too small to cause any issues.

jrockway 3y ago
> Since on a narrow-body aircraft passengers can easily be within 2 meters of some of the VHF antennae. But, separated by a very large piece of conductive metal. (I think even carbon fiber planes have a conductive layer in there, to prevent damage from lightning strikes.)
- skykooler 3y ago
  Isn’t carbon fiber conductive itself?
  - tonyarkles 3y ago
    Carbon fibre is definitely conductive. A couple of years ago I measured a 1” diameter tube and got about 15ohms/ft.
    - Animats 3y ago
      Right, it's a resistor. This is a problem for airframes and wind turbine blades. Its resistance is too high to deal well with lightning. So aluminum is needed to provide a conductive path.
  - thenickdude 3y ago
    Yes, and blocks radio transmissions very nicely. When making a model airplane with a carbon fibre hull, we have to add a plain fibreglass or plastic window for the antenna to receive through.

PM_me_your_math 3y ago

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