[VK3YE] knows there are at least two things wrong with the cheap antennas you get with most SDR dongles. First, they are too short. You’d like to have enough to pull out a quarter wavelength on the longest frequency you want to operate. The second problem is there’s no real ground. He fixed both of these problems, as you can see in the video below.
The result might be called an ugly duckling rather than a rubber ducky. But it does seem to work. You could probably come up with something nicer to reseal the base, but the tape does work. A nice 3D printed housing would work, too, and might improve the appearance. We also thought about the goop you use on tool handles.
We actually have simply cut these antennas off and reused the cable and connector to hook up a better antenna. You might get more mileage out of that approach. On the other hand, the magnetic base and reasonably small form factor is pretty attractive.
If you want to do before and after testing, we’d suggest using Python. Or, just bite the bullet and build something that looks like it belongs in a movie.
> just bite the bullet and build something that looks like it belongs in a movie.
But that’s for circular polarization; unless you want to do something with satellites, or very specific directive microwave links (which makes little sense given the RTL-SDR’s frequency range), you don’t need one of them; they are inherently half as good at picking up linearly polarized signals (i.e. most stuff) than a linearly polarized antenna of the same size!
Karen Rucker did a nice introductory video about antennas: https://hackaday.com/2021/07/15/new-video-series-learning-antenna-basics-with-karen-rucker/ I don’t think she goes into cross-polarization loss in the first video, so but it might be helpful to know the fundamental difference between these antennas :)
Best signal improvement with those antennas – stick it to central heating radiator. It provides big grounded plane and sometimes it’s a difference between almost no signal and very good signal.
The video talks of connecting a “radial”(?), the article about real ground.
I do not know a lot about these things, but am interested (own a RTL-SDR).
Can anyone elaborate?
Wikipedia has an overview: https://en.wikipedia.org/wiki/Radial_(radio); in this case the reference is to what the page calls “grounding radials” – so named as they are usually placed such that they extend radially from the antenna.
Thanks mate, will check it out.
My dad would walk around with a radial dragging from his pocket on his portable radio it seemed to improve the signal.
You might also see reference to something called a counterpoise. It’s a wire cut to be quarter-wavelength resonant at a specific frequency and provides an artificial ground at that frequency. Think of it as the bottom half of a dipole.
I’ve used a mag mount whip on a trash can at 120 MHz and it worked well enough. Yes, I was talking to an aircraft.
A Radial and Counterpoise, as used here are the same thing. Neither one necessarily implies it must be 1/4 wavelength long by name. A basic “Ground Plane” Antenna, typically uses a 1/4 WL vertical element and one or more radials (counterpoises) also roughly 1/4 WL long.
My idea… Use a motorized car antenna,, so you can remotely adjust the antenna.
I’ve seen people use metal tape measures to make portable, variable length antennas.
Or the classic slinky.
Can you still get those these days?
They are illegal as they pose a chocking hazard.
Whose stupid kid is trying to eat entire slinkys in one bite?
They think if they swallow a Slinky, they can slink down ty thee stairs.
I did something similar with my antenna. I peeled the insulating bottom off, but instead of attaching a wire to the bottom I just put it on a cookie sheet. Then it acts like a big monopole antenna. And it provided a good weight so it wouldn’t fall over.
Seemed to work just fine.
That tool handle goop is called Plasti-Dip. There is also liquid electrical tape, which smells like brain damage but works very well.