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
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