261–270 of 353 posts
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In Iran right now... Internet shut down while the regime keeps slaughtering people at the order of 4x9/11.
Internet is exploited by US as a tool for regime change [1] in coordination with sponsored on the ground terrorism. [1] [1] Washington’s War on Iran: The Importance of Defending Information Space https://www.youtube.com/watch?v=yiJm4zwZZHY
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It is not as easy as you think. RF attenuation is proportional to frequency and at 2.4 GHz, it is very high. Also, the distance over which one could communicate depends on antenna height, so if both parties are at ground level, it is not feasible over a few hundred meters unless both are in wide open space. Source: ham operator who has played with long distance device to device communication without using a repeater.
> RF attenuation is proportional to frequency and at 2.4 GHz, it is very high. Through building materials, foliage etc, but not in free space/line-of-sight. > Also, the distance over which one could communicate depends on antenna height, so if both parties are at ground level, it is not feasible over a few hundred meters unless both are in wide open space. Isn't it just the opposite? Antenna height is only the limiti…
Yeah. Even in free space. For example, attenuation at 1 km for 144 MHz (ham VHF band) is about -76 dB while for 2.4 GHz, it is about -100 dB. That 24 dB drop could mean, the signal is below the noise floor of your receiver unless you increase the RF power output which means more battery drain.
For example, BT audio gets cut just moving to the next room despite the RF power of BT transmitters being ~ 5mW( 7 dBm ) and at 10m, the attenuation is -60 dB(just free space loss which is ideal condition), so 53 dBm (7-60) at the receiver is usually sufficient, yet they struggle.
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> Meanwhile a $10 walkie talkie using primitive stone-age radio technology can go many miles with zero infrastructure, but by law is not allowed to be used for data transmission. Is this even true? I still have two Gotennas from before they pivoted to military use cases, and they were legal to use both in the US and in Europe (on different bands auto-configured via GPS, as far as I remember). REI also currently stock…
Get bought out by military control grid --> Instantly kill popular consumer devices.
I guess anything that's useful to regular hikers is potentially also useful to the armed, abroad type of hiker, and these are usually better funded, so I can see why startups like these would pivot.
This feels like something Apple should do with iPhones. Find My and air tags was already a huge success because of the ubiquitous nature of iPhones. Apple could add this to iPhone, sell it as privacy focussed. Let you message anyone in your iMessage contacts with a new bubble colour. Propagate over Bluetooth when you don't have internet. I can see a snazzy Apple reveal for this showcasing it's use on a cruise ship, i…
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> RF attenuation is proportional to frequency and at 2.4 GHz, it is very high. Through building materials, foliage etc, but not in free space/line-of-sight. > Also, the distance over which one could communicate depends on antenna height, so if both parties are at ground level, it is not feasible over a few hundred meters unless both are in wide open space. Isn't it just the opposite? Antenna height is only the limiti…
> Through building materials, foliage etc, but not in free space/line-of-sight. Yeah. Even in free space. For example, attenuation at 1 km for 144 MHz (ham VHF band) is about -76 dB while for 2.4 GHz, it is about -100 dB. That 24 dB drop could mean, the signal is below the noise floor of your receiver unless you increase the RF power output which means more battery drain. For example, BT audio gets cut just moving to…
> For example, attenuation at 1 km for 144 MHz (ham VHF band) is about -76 dB while for 2.4 GHz, it is about -100 dB.
This is a common misunderstanding of the free-space path loss formula, which is expressed in terms of the idealized isotropic radiator, the length of which is frequency-dependent. In other words, this calculation is assuming a proportionally (much) smaller antenna for the 2.4 GHz case.
With the same antenna size, the path loss is exactly the same. After all, where else should the radiated energy go?
It's criminal that cell phones are bristling with incredibly advanced radio technology and yet they are by law not allowed to communicate directly with each other over a distance of more than a couple hundred meters without assistance from a licensed and centrally controlled base station. Meanwhile a $10 walkie talkie using primitive stone-age radio technology can go many miles with zero infrastructure, but by law is…
Personally, the additional complexity and overheads required for a P2P phone network is not worth while and I'm not sure it would fix that many problems that haven't already been fixed with walkie talkies.
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To have an FM receiver work on a phone, you do need an antenna, the wired headphones serve that purpose perfectly. An FM transmitter is easy to find; you can use the simple 'Jack-to-FM' adapters designed for car radios, or much better, a USB SDR (which can range from a few kHz to GHz). Regarding the 'protocol for the waves,' you'll need to play with modulation. That’s the fun part. In technical literature, there are…
hm, than i think it's better to use the LORA stuff, no? if i need an external device with my device anyway, i can use one of them. because the fun thing is cool, but people want some usable...
If the requirement is to communicate where consumer standards like Bluetooth fail, like in a ship, you have to choose the system for the environment. I evaluate these choices like an architect building a robust system, rather than just using what is available at the nearby shop.
It's criminal that cell phones are bristling with incredibly advanced radio technology and yet they are by law not allowed to communicate directly with each other over a distance of more than a couple hundred meters without assistance from a licensed and centrally controlled base station. Meanwhile a $10 walkie talkie using primitive stone-age radio technology can go many miles with zero infrastructure, but by law is…
This feels like something Apple should do with iPhones. Find My and air tags was already a huge success because of the ubiquitous nature of iPhones. Apple could add this to iPhone, sell it as privacy focussed. Let you message anyone in your iMessage contacts with a new bubble colour. Propagate over Bluetooth when you don't have internet. I can see a snazzy Apple reveal for this showcasing it's use on a cruise ship, i…
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> Through building materials, foliage etc, but not in free space/line-of-sight. Yeah. Even in free space. For example, attenuation at 1 km for 144 MHz (ham VHF band) is about -76 dB while for 2.4 GHz, it is about -100 dB. That 24 dB drop could mean, the signal is below the noise floor of your receiver unless you increase the RF power output which means more battery drain. For example, BT audio gets cut just moving to…
No, attenuation in vacuum is exactly the same, and the difference between humid air, dry air, and vacuum doesn't really matter at frequencies below a few GHz. > For example, attenuation at 1 km for 144 MHz (ham VHF band) is about -76 dB while for 2.4 GHz, it is about -100 dB. This is a common misunderstanding of the free-space path loss formula, which is expressed in terms of the idealized isotropic radiator, the len…
What do you mean? The size of the dipole or monopole antenna is dependent on the wavelength, so obviously the 2.4 GHz is just a few centimeters and not the same size as a VHF antenna.
> After all, where else should the radiated energy go?
Well, most of RF energy is wasted. There are software that can plot the radiation pattern, but even without knowing the exact pattern, very little RF energy is received at the target.