John, I've done some further experimentation. My units are the full size K3/0s, so it's unlikely any low pass filtering is in place. I checked the continuity between pin 1 of the 8 pin front mic connector and the tip connection on the rear mic connector and found they are tied together measuring less than 10 ohms. The very fine traces on the circuit board might account for this resistance. Sadly no schematic or board layout is available to confirm. The PTT from pin 2 on the 8 pin mic connector also checks to be directly connected to the rear PTT RCA jack. So this tells us the "local" K3/0 settings do nothing to change the mic audio. I also determined the problem is a ground loop where noise from the RRC control unit is being picked up by the interconnecting mic leads. After adding further ground loop isolation directly at the rear 1/8 mic jack with a 600/600 ohm transformer removes all the noise. This might have been my final solution but you cannot pass DC mic bias through a transformer if you need it.
But next the real answer! Close inspection of the "factory" AUX/MIC cable from Remoterig shows no conformity to the schematic provided in the manual! The cable provided is a 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 cable with longer shielded wires connected to a very short piece of CAT 5/6 at the RJ45 works much better! Leaving a long length of exposed mic cable is not good practice. This may work OK with high level signals but is a no-no for low level mic signals. A shielded piece of CAT 5/6 might also work. 73, John W1AN -- View this message in context: http://elecraft.365791.n2.nabble.com/Is-K3-0-Audio-pass-through-or-processed-in-K3-0-tp7613427p7613521.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
