yes i know how spread spectrum schemes work, but this is not really practical or relevant here
for spread spectrum things to work you need some wide bandwidth, this works great for microwaves where you can spread your 90GHz band signal so that it covers 5GHz, you can’t have a signal centered on 5MHz that is 5GHz wide; HF is relevant because while microwaves work with this microwaves are line of sight only and most people’s line of sight still terminates in their own country. if you live on a lone hill next to border good for you, but the rest would need to use HF to get out, and there’s simply not that much bandwidth available in the first place, which would make any scheme like this extremely slow if at all viable. and you can still jam it
i don’t assume that satellite repeaters would be a viable option because satellite, or any other receiving party for that matter, would need to be aware of modulation scheme to receive it in the first place, so it only works if your international contacts are pre-arranged, and even then you need radio that has much larger bandwidth that is usually available. yapping on LSB or narrow digimodes will get you heard within continental range, but also it will get you noticed, but if you hide from your adversary you also hide from everyone else not in the know. and even then, you can still get noticed, because it’s under noise level only at some distance from you
also some of these schemes require precise time to be known, and if you have gps jammed you’ll get extra problems from that
You could also resort to good old code books and hide your communication in plain sight, instead of trying to evade surveillance with technical tricks that are easily detected.
A compact antenna for long bandwidth: wind a spiral. For 40 meters, you could could make a spiral of 1.6 m outer diameter (“a bit less than average human height”), 10 cm inner diameter and 15 turns of wire (if I used the calculator correctly). Not a terribly efficient antenna, but a very compact one for given wavelength.
(I especially like the last one, third generation is made of copper tape and sized like a laptop computer, and the guy in Sweden is getting reception from as far as the Far East.)
I have heard (myself I don’t use HF) that HF radios work tolerably with an antenna horizontally on a car roof (could be a truck bed). But it’s true that there is little bandwidth on such frequencies. As for throughput: a channel that is 9 KHz wide is supposed to transfer 9.6 kbit / s with military data radios (with ionosphere reflection, despite all the multipathing that it causes - I have not checked, but recall a scientific paper telling so). A reasonable detection avoidance technique might be broadcasting from a depressed location or an urban canyon with tall ground clutter. You’d want the direction finder to chase reflections.
Even more fun scenarios exist: launch your guerilla transmitter on a free flight balloon, and will have plentiful line of sight. Essentially a pseudosatellite.
this is just a really extravagant heater, physics forbids antenna this small to have good radiation resistance. for your contrived below noise communications scheme, you need more bandwidth that is physically possible on hf, yet you choose antenna design that is even less wideband than regular dipole. 40m of wire is for 80m band, which is usable more often in this configuration, ignoring everything else
As for throughput: a channel that is 9 KHz wide is supposed to transfer 9.6 kbit / s
5500kbps in extremely favourable conditions is your peak attainable speed, bandwiths in normal radios are narrower
A reasonable detection avoidance technique might be broadcasting from a depressed location or an urban canyon with tall ground clutter
if you don’t want anyone to hear you
launch your guerilla transmitter on a free flight balloon, and will have plentiful line of sight.
with what power source? better study for and get your license, start using radio and stop embarrassing yourself
Which of them? The Swedish guy’s copper tape antenna?
with what power source?
High altitude pseudosatellites (look up the term, they’re fun) almost unexceptionally use battery and solar. I don’t propose carrying a steam engine. :)
better study for and get your license
For what? To make my drones find their way home better? I’m not a radio amateur and I don’t need or intend to be. I build stuff that flies, uses gigahertz frequencies and navigates using radio. I admit I know little of HF, but I know the basics acceptably. No need to assume a holier than thou attitude.
5500kbps in extremely favourable conditions is your peak attainable speed
Well, some people write: “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.”
Maybe the they are wrong, maybe I read them lazily. Regardless, you can send SMS just as nicely with 5 kilobits per second as you can with 9 kilobits. But as I said, I haven’t tested and don’t intend to test. I approximately know what HF does and how it propagates, but don’t use that band in practise.
By the way, the same people write:
In [5] a car-mounted vertical half loop antenna is described, using capacitance loading to achieve an NVIS antenna gain between −12 and −10 dBi from 3 to 8 MHz.
yes i know how spread spectrum schemes work, but this is not really practical or relevant here
for spread spectrum things to work you need some wide bandwidth, this works great for microwaves where you can spread your 90GHz band signal so that it covers 5GHz, you can’t have a signal centered on 5MHz that is 5GHz wide; HF is relevant because while microwaves work with this microwaves are line of sight only and most people’s line of sight still terminates in their own country. if you live on a lone hill next to border good for you, but the rest would need to use HF to get out, and there’s simply not that much bandwidth available in the first place, which would make any scheme like this extremely slow if at all viable. and you can still jam it
i don’t assume that satellite repeaters would be a viable option because satellite, or any other receiving party for that matter, would need to be aware of modulation scheme to receive it in the first place, so it only works if your international contacts are pre-arranged, and even then you need radio that has much larger bandwidth that is usually available. yapping on LSB or narrow digimodes will get you heard within continental range, but also it will get you noticed, but if you hide from your adversary you also hide from everyone else not in the know. and even then, you can still get noticed, because it’s under noise level only at some distance from you
also some of these schemes require precise time to be known, and if you have gps jammed you’ll get extra problems from that
You could also resort to good old code books and hide your communication in plain sight, instead of trying to evade surveillance with technical tricks that are easily detected.
Thanks for contructive criticism. :)
A compact antenna for long bandwidth: wind a spiral. For 40 meters, you could could make a spiral of 1.6 m outer diameter (“a bit less than average human height”), 10 cm inner diameter and 15 turns of wire (if I used the calculator correctly). Not a terribly efficient antenna, but a very compact one for given wavelength.
Examples:
https://sergeev.io/projects/spiral-dipole/
https://www.avalonarc.org.uk/2019/10-27-an-80m-spiral-loop.html
https://sa0pej.wordpress.com/build-page-nvis-spiral-loop-antenna/
(I especially like the last one, third generation is made of copper tape and sized like a laptop computer, and the guy in Sweden is getting reception from as far as the Far East.)
I have heard (myself I don’t use HF) that HF radios work tolerably with an antenna horizontally on a car roof (could be a truck bed). But it’s true that there is little bandwidth on such frequencies. As for throughput: a channel that is 9 KHz wide is supposed to transfer 9.6 kbit / s with military data radios (with ionosphere reflection, despite all the multipathing that it causes - I have not checked, but recall a scientific paper telling so). A reasonable detection avoidance technique might be broadcasting from a depressed location or an urban canyon with tall ground clutter. You’d want the direction finder to chase reflections.
Even more fun scenarios exist: launch your guerilla transmitter on a free flight balloon, and will have plentiful line of sight. Essentially a pseudosatellite.
this is just a really extravagant heater, physics forbids antenna this small to have good radiation resistance. for your contrived below noise communications scheme, you need more bandwidth that is physically possible on hf, yet you choose antenna design that is even less wideband than regular dipole. 40m of wire is for 80m band, which is usable more often in this configuration, ignoring everything else
5500kbps in extremely favourable conditions is your peak attainable speed, bandwiths in normal radios are narrower
if you don’t want anyone to hear you
with what power source? better study for and get your license, start using radio and stop embarrassing yourself
Which of them? The Swedish guy’s copper tape antenna?
High altitude pseudosatellites (look up the term, they’re fun) almost unexceptionally use battery and solar. I don’t propose carrying a steam engine. :)
For what? To make my drones find their way home better? I’m not a radio amateur and I don’t need or intend to be. I build stuff that flies, uses gigahertz frequencies and navigates using radio. I admit I know little of HF, but I know the basics acceptably. No need to assume a holier than thou attitude.
Well, some people write: “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.”
Maybe the they are wrong, maybe I read them lazily. Regardless, you can send SMS just as nicely with 5 kilobits per second as you can with 9 kilobits. But as I said, I haven’t tested and don’t intend to test. I approximately know what HF does and how it propagates, but don’t use that band in practise.
By the way, the same people write:
Example:
https://airadio.com/hf-ssb-commercial/barrett-communications/2018-mobile-magnetic-loop-hf-antenna