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Hardware, Cabling, Installations / Mic audio Noise from K3/0 to Control RRC problem resolved.
« on: 2016-02-04, 19:59:26 »
I'm currently setting up another K3/0 (non-mini) twin system and experienced ground loop or noise ingress through the interconnecting mic cable. I've determined I could eliminate the noise by using a 600/600 ohm transformer directly at the rear mic jack on the K3/0 to supply the RRC control. This might have been my final solution but you cannot pass DC mic bias through a transformer if you need to use a condenser mic. My initial setup is thru the front K3/0 8 pin connector using the Heil Proset with a much lower audio level.
Close inspection of 2 of the "factory" AUX/MIC cables show no conformity to the schematic provided in the manual! The cables provided are lengthy CAT5/6 4 pair cable with short breakouts at the end with the PTT RCA connector and 1/8" mic connector. This factory cable is unshielded. Wires used for mic audio and mic return are from separate pairs, not from one twisted pair. Consequently, shielding is close to non-existent. PTT wiring is similar. Making up my own cables with longer shielded wires connected to a very short piece of CAT 5/6 at the RJ45 work much better! Leaving a long length of exposed mic wire is not good practice. This may work OK with high level signals and the majority of installs, but is a no-no for low level mic signals. A shielded piece of CAT 5/6 might also work for a starting point. If you are experiencing noise ingress you may wish to look at the cables.
73, John W1AN
Close inspection of 2 of the "factory" AUX/MIC cables show no conformity to the schematic provided in the manual! The cables provided are lengthy CAT5/6 4 pair cable with short breakouts at the end with the PTT RCA connector and 1/8" mic connector. This factory cable is unshielded. Wires used for mic audio and mic return are from separate pairs, not from one twisted pair. Consequently, shielding is close to non-existent. PTT wiring is similar. Making up my own cables with longer shielded wires connected to a very short piece of CAT 5/6 at the RJ45 work much better! Leaving a long length of exposed mic wire is not good practice. This may work OK with high level signals and the majority of installs, but is a no-no for low level mic signals. A shielded piece of CAT 5/6 might also work for a starting point. If you are experiencing noise ingress you may wish to look at the cables.
73, John W1AN