Long range communication with just 1W of power?

Question

Is it possible, and how can I setup communication between stations 1000km apart from each other by using just 1W of transmission power?

By communication, I mean:

• It can be text based
• It can be very slow. It's okay if I receive a small message in few hours of time.

What are the limitations:

• I don't have an amateur license
• I can use only 27MHz CB radio band
• Maximum radiated power can't be more than 1W
• Many busy cities will be between the two stations, not just plain fields and seas.

What I have/can do:

• Use a directional antenna
• I like DIY
• I am planning to receive using an RTL-SDR
• I can use open-source software to decode signals and/or can write a script to do so, too.

I am from India and here is the latest I could find for CB radio band. Also, it seems I could use 5W of power, but no external antenna and no mention of data transfer policy.

I was amazed how far WSPR signals can go with very little power. Trying to achieve something like that. Not just beacons, but actual communication.

If anything I asked doesn't make sense, I'll keep on editing the question as per the community's feedback, to be more specific.

Answer 1

At 27 MHz and a distance of 1000 km, propagation will be the main determinant of the possibility of communications. Propagation will primarily be a factor of time of day and the sun spot conditions. You can get a fairly accurate estimate by using propagation prediction sites such as VOACAP.

If your interest is exchanging messages between stations, one of the best weak signal modes is FT8 which is part of the free WSJT-X software. A similar, derivative work is JS8CALL.

Take care, however, to check your local regulations to see if data modes are permitted on these frequencies. This would not be allowed in the US, for example.

With that being said, why don't you and your friend become ham radio operators? The effort and expense to get a license in India is not very much. For a restricted grade license you don't even need to know morse code. It will give you the option for more power and many more frequencies, some of which are more suitable to reliable communications.

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Answer 2

I would say, your task is a challenging one, but not unsolvable. 27 MHz CB radio band should work similar to 10m amateur radio band.

I suggest to start with simple experiments. For instance, solder a simple oscillator. In my experience Clapp oscillator is quite simple to solder, see schematic in this article https://eax.me/clapp-oscillator/ . Then add a 555 timer to turn it on and off. Now you have a simple CW beacon.

Then use the beacon on transmitting side and RTL-SDR on receiving side. Experiment with antennas, power, observe the propagation during different time. If you receive a beacon, even a wery weak signal, now you can start experimenting with different modes.

Also I would like to note that in some countries it's illegal to use a directional antenna in CB.

Answer 3

If you have the ability to use a different wavelength band, you might want to investigate (including your local licensing requirements) use of 20, 40, or 80 meter and CW (Morse code). American QRP (low power) operators have a certificate for "1000 miles per watt" (that would be 1600 km per watt), which I've seen referred to as almost a joke, because it's so easy to do in the American CW bands. In part, this is easy because 40m and 80m, especially, propagate well, and in part because CW makes more efficient use of radiated power by transmitting on a narrower bandwidth.

What you're proposing isn't impossible, at all, even in 27 MHz/11m band; during the American CB heyday of the late 1970s, I recall hearing transmitters that were limited by law to 5 watt input or 4 watt output (depending on date of manufacture) from several hundred miles away, with no real attempt to optimize transmission (i.e. using off the shelf antennas on mobile installations). With single sideband rigs and optimized antennae, it was common to talk to other stations across the width of the North American central plains, from Montana to Florida (nearly 3000 miles, or around 4500 km) with that power level, at night when the "skip" was good.

With the limitations you have on radiated power and terrain, even if you're stuck in 27 MHz band, I'd seriously suggest investigating something akin to machine-sent and machine-received CW. There's a Linux program called fldigi that's free and open source, and is in the repositories for Ubuntu (at least 16.04, probably 14.04 and 18.04 as well) that can manage both sending and receiving International Morse at any reasonable rate -- even very slow, if that's what you need to make you connection work. It also handles many other digital radio formats, though use of other than Morse may be limited by law to certain bands and licenses.