I got some down time this afternoon and decided to scan the spectrum of my cable modem's coax line using my RTL-SDR dongle. I connected up the cable using an MCX type F adapter, then plugged the dongle into a USB extension cable and finally plugged the cable into my laptop. As soon as I did this a big 3 inch spark shot out of the USB port and of course, I unplugged the dongle right away and disassembled the rest. After testing various things I have determined there is not a short in the dongle or cable, and there is not high voltage on my USB ports. The arc occurred on the outer shielding of the connector and charred it pretty good. This shielding is tied to the ground pin by the SDR.
What's strange is nothing was damaged... and I tried this the exact same way before using a Charter line for my cable box. The only thing I can think of is perhaps the shielding of the dongle is absorbing transient RF emissions from the cable (building up voltage on the connector) and it simply discharged to ground when I plugged in the cable. I also verified there is no high voltage on the coax line itself. No magic smoke anywhere.
Has anyone had a similar experience with receiving dongles or just RF feed cables in general? Is the above scenario a possible cause for what I saw? Do these types of lines typically use DC power injectors?
What's strange is nothing was damaged... and I tried this the exact same way before using a Charter line for my cable box. The only thing I can think of is perhaps the shielding of the dongle is absorbing transient RF emissions from the cable (building up voltage on the connector) and it simply discharged to ground when I plugged in the cable. I also verified there is no high voltage on the coax line itself. No magic smoke anywhere.
Has anyone had a similar experience with receiving dongles or just RF feed cables in general? Is the above scenario a possible cause for what I saw? Do these types of lines typically use DC power injectors?
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