HFU HF Underground
Technical Topics => Equipment => Topic started by: ChrisSmolinski on January 18, 2015, 2042 UTC
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Earlier today I had an interesting problem - mixing products from MW stations all over HF. I actually noticed it a few times on the overnight SDR recording as well. I could not hear them on another radio, so that seemed to rule out them being "real", but instead being something produced specifically by the one radio.
After checking a few things out, I noticed one of the barrel connectors on the incoming coax, connecting two sections, was loose. I tightened it, and immediately the mixing products all vanished. The signal levels went up a little, as well. Perhaps something in the loose connection (dirt, etc) was acting like a rectifier?
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Ah, you've stumbled upon the rusty bolt effect :)
https://en.wikipedia.org/wiki/Rusty_bolt_effect (https://en.wikipedia.org/wiki/Rusty_bolt_effect)
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I've had this happen a couple of times over the years. The first time, I thought my receiver had something very wrong with it. Once I calmed down, I retightened all my connections and it disappeared. About the same time, I had a "mystery carrier" in my NRD-515 that stumped me until I checked the interconnect cables inside it. It was just one of the interconnect plugs (really cheap cables with crimped connections!) had oxidized and was causing it. I soldered all the plugs and put De-Oxit on the jacks and never had another issue with it again.