Linking this with some sound modem to transmit text data, ideally with some automatic repetition to remove errors, will probably be much nicer to communicate with. But cool concept overall.
What makes me worry is the size of the “reflector”. I wonder what symbol rate it is possible to get if the “reflector” is literally everywhere above you - the time delay between start of reflection and end of reflection might be considerable.
I found a resource with practical advise about using NVIS, including using meteorological data (ionograms) to determine the best frequency, antenna diagrams and such. (His drawings are in Spanish, but I think most English-speakers can decode Spanish antenna diagrams with a few clues, since meter is metro, and frequency is frecuencia.)
Some additional interesting antenna designs (vertical yagi on ropes, spiral antenna, etc) and propagation shemes, can be found in this research paper.
They have a passage which addresses data rates, and the data rates are poor…
In [110] two alternative channel access technologies are tested and compared in wireless mesh networks: Automatic Link Establishment (ALE) and fixed-frequency MAC protocols. These are also described in the book of Johnson et al. [111]. In [112] we find measurements on a MIL-STD-188-110C [113] link over distances of up to 160 km, providing the users with bit rates up to 9.6 kbps in 6–9 kHz RF bandwidth. The standard gives the option of selecting bandwidth and modulation, and includes wideband modulation with up
to 24 kHz bandwidth with elaborate coding and interleaving.
So, some military radios use a narrow slice of 6…9 KHz for each channel and push 9 kilobits per second. Widening the slice used will give more speed. Enough to send SMS, I would say. A text of 1000 characters could be 8 kilobits, and would require initial air time for 1 second (+ exponential back-off resends, most likely). Let’s assume a total of 3 transmission events per message. An hour contains 3600 seconds, divide by 3 --> a channel at 100% capacity could accommodate 1200 messages per hour.
Linking this with some sound modem to transmit text data, ideally with some automatic repetition to remove errors, will probably be much nicer to communicate with. But cool concept overall.
What makes me worry is the size of the “reflector”. I wonder what symbol rate it is possible to get if the “reflector” is literally everywhere above you - the time delay between start of reflection and end of reflection might be considerable.
I found a resource with practical advise about using NVIS, including using meteorological data (ionograms) to determine the best frequency, antenna diagrams and such. (His drawings are in Spanish, but I think most English-speakers can decode Spanish antenna diagrams with a few clues, since meter is metro, and frequency is frecuencia.)
https://www.ipellejero.es/hf/NVIS/english.php
Some additional interesting antenna designs (vertical yagi on ropes, spiral antenna, etc) and propagation shemes, can be found in this research paper.
They have a passage which addresses data rates, and the data rates are poor…
So, some military radios use a narrow slice of 6…9 KHz for each channel and push 9 kilobits per second. Widening the slice used will give more speed. Enough to send SMS, I would say. A text of 1000 characters could be 8 kilobits, and would require initial air time for 1 second (+ exponential back-off resends, most likely). Let’s assume a total of 3 transmission events per message. An hour contains 3600 seconds, divide by 3 --> a channel at 100% capacity could accommodate 1200 messages per hour.