Kv4p HT – A homebrew 1W radio (VHF or UHF) that plugs into an Android phone
kv4p.com
kv4p.com
Airdrop was the closest thing we had, and even that has been intentionally nerfed for non-contact senders.
It's absurd that modern phones can talk to satellites hundreds of kilometers above, but not to other phones a few meters away in the same room, airplane cabin, train car etc.
The providers don't want it because they can't charge you for it. The governments don't like to see people communicate outside of their control. See how Apple caved to China making AirDrop no longer public and has followed suit in the rest of the world because other governments fear this capability too.
Also, the hardware for good peer to peer communication is just not present in regular phones. Some libre hardware projects do have optional addons for LoRa, such as the PinePhone: https://pine64.org/documentation/Phone_Accessories/LoRa/
Perhaps you mean p2p phone calls. Fine - although I have a hard time believing that the 900 Mhz radios capable of talking to a tower literal miles away are physically incapable of talking to each other. They're just programmed not to. In any case, the inconvenience and unreliability of sending files 3 feet, vs the streamlined experience of sending them via a corporate datacenter thousands of miles away, demonstrates that this is not about hardware. This is about software, and by extension about control.
Hence LoRa. Yes, 5G would be an option but the licensed spectrum (and firmware restriction) makes that impossible.
>It's absurd that modern phones can talk to satellites hundreds of kilometers above, but not to other phones a few meters away in the same room, airplane cabin, train car etc.
Common everyday filesharing, not meshnet fantasies.
You can still do that! It never went away.
It just led me to finding this:
worth a bookmark.
I see they use those cheapo Chinese RF modules (SA818). I've seen those also with SDR input/output, that's interesting. The underlying chip is very similar: The chip that will be used in this module is the RDA1846. This is a chip that's in most Chinese handhelds and is internally fully SDR but it decodes to analog. There's also the RDA1847 with similar pinout which offers the raw SDR stream and can thus be used for any mode, but with the added complexity of having to do the SDR decoding externally.
That means that this design could probably also be modified to do DMR. Though the SDR side might be a little bit too much to ask of an ESP32. On the other hand, it is only a very low bitrate signal.
So maybe the 1w is also a regulatory issue.
But in general, yeah, unless you do it regularly, living near sensitive facilities (airport, military base, hospital, factories, research labs etc) or deliberately transmitting at/near emergency frequencies (police, paramedic etc) at most you'll get yelled by a pissed off operator (at that point, stop, they could be already coordinating with someone else to triangulate you)
https://www.fcc.gov/reports-research/guides/fcc-enforcement-...
People tinkering and staying away from ham bands will generally be fine and for the cheap ham gear that made easy by design usually by doing a factory reset or worst case having to clip a diode to widen their frequency ranges. Most ham gear is designed to be highly hackable.
That said, no one is going to stop you from squatting on 146.580 MHz for example, a frequency commonly used by outdoors folks, rules notwithstanding.
With a ham license the limit is 1.5kW, without one its zero
How far can such a device reach in a typical urban environment with the longer antenna?
The only thing that really helps extend the range is elevating the antenna, and repeaters allow you to do that even between two mobile stations.
You are right that handheld radios wont get more than about 10km, but that is due to the curvature of the earth. Mountain top to mountain top, you could easily do 50-100km
That's even true for the L- and S-band; otherwise you wouldn't be able to use a cell phone in a windowless room, for example. (Much of what's commonly attributed to "object penetration" is actually mostly due to reflections and diffraction around obstacles.)
Most radio amateurs would utilize a repeater to get over this limitation. Assuming there is a reliable repeater one is welcome to use nearby.
We need a compact short wave transceiver device actually.
And I know, I know, Baofengs are notorious for going over the allowed noise limits… but still…
Several handheld CB radios exist, with little loaded whip antennas. You can go buy one. You'll see. They work for talking between two tractors in a field or whatnot. Past that, not so much. Today, you're better off with license free UHF handhelds for that use case.
I have personally made voice (single-sideband or SSB, which is analog like AM without wasting energy transmitting a carrier or redundant sideband) contacts with a 5 watt portable (Elecraft KX2) between countries in Europe, using a meter-long whip antenna and a trailing counterpoise wire.
These radios are incredibly complex weak-signal equipment, and that is reflected in the price.
That said, it is fun. Using morse code to do the same is even more fun.
I would never rely on this for off-the-grid communication, though.
Handheld CB radios do exist and are cheap, but I've never really used them.
Most people know that just about every Android phone has a restricted hardware design, not an expandable one.
So, "turn your phone into X" is bound to automatically evoke images of another device that plugs into the phone via common connectors like USB or the audio jack and an app on the phone to control that device. That's what the phrase means to most people in the context of Android.
"Turn your phone into a ham radio transceiver controller" is neither needed nor entirely accurate, because then people will assume it can control _any_ ham radio transceiver.
The title is still misleading to me. Not terribly so – hence my not quite serious reply – but I was expecting something like https://timestation.pages.dev/, which actually transmits using included hardware only.
However, your analogy is not equivalent to, nor an example for, what I said. There's a difference between a phone's own USB/audiojack interfaces and a wall outlet.
The two don't add up, and your apologetic analysis doesn't convince me otherwise. It's still clickbait. An Android cell phone has radio guts, and that headline is just gutless.
I've used a few handheld transcievers and they tend towards clunky user interfaces-- tiny, fiddly displays, highly modal keys, and basically needing to memorize the manual to use it.
Even worse-- there's not a strong correlation between the quality of the RF unit and the user-interface. The Yaesu FT-60 is a reliable, high-quality radio, with all the user friendliness of a live porcupine.
But with a 6-inch pocketable touchscreen you could solve most of the UI problems, and focus on the radio problems.
Keeping the division also gives you flexibility-- you could design a 25-watt tabletop unit, or modules for different bands, that shared the same basic control software and UI