Postby Roger » Sun Feb 10, 2019 5:17 pm
In order to receive a signal you need to have an antenna with two sides. A dipole, for example, has two wires connected to a feedline (like twinlead or coax). A vertical antenna has one element (wire, mast or whip) and uses a ground or counterpoise as the other.
So what is happening in your case when you only have a balun connected to your RSP and no antenna attached to the balun? You still have an antenna system but it is a poor one and only able to receive very strong signals. One side of the antenna is the USB cable and the other side is the short connecting wire from the RSP2 circuit board to the SMA terminal and your attached balun. This poor antenna will pickup strong signals and local noise (RFI).
USB cables vary considerably in quality. The best ones have the wires twisted and shielded with an outer shield encasing all the wires. They also have a quality toroid but these are generally used to reduce cable radiation above 30 MHz. Tripp-Lite makes quality cables but even these should have external toroids (Mix 31 works well) to reduce noise pickup on the HF bands. Here is what I use and it works well on HF.
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- USB Cable.jpg (138.55 KiB) Viewed 225 times
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