I’ve been watching the Solder Smoke direct conversion receiver challenge build and thinking of maybe building it from parts I already have laying around… assuming I wind my own toroids. I haven’t noticed anyone talking about antenna stuff. What is the deal here?
This is the principal video series primer: https://www.youtube.com/watch?v=rLjxU2rMeXw
It is also on hackaday too.
Is there some rule about antenna where a more specialized element is required at specific frequencies? I know I’m missing fundamental practical information here as the wave length for 7 MHz is around 43 meters. Even a quarter wave length would involve a house spanning wire. So what gives, what high school fundamental have I forgotten?
The gist of it is that antenna length can be “faked”. Sure, it’s not as good as matching the wavelength (or a fraction thereof) with your antenna, but it is possible to have a shorter antenna and have parts of the length being an inductive (or capacitive? I forget…) load that makes up for the missing length.
Source: Used to do a lot if MF/HF installs on ships. Right before the actual antenna we use a Tuner, which is basically additional loads that helps matching the frequency. When transmitting on a new frequency, you key in the radio to let the tuner do its job, and then you rekey to do the actual talking. When the tuner is adjusting to the new frequency you can actually hear a series of relays clicking inside to connect the necessary loads.