I have a 67-foot elevated vertical that I can use on 80 and 40, and it works fine on CW. However, on SSB, both bands, there clearly is feedback; there is no feedback on the other bands where I use a C3 yagi.
Elevated verticals will treat the [outside of the] feedline as a random length radial. The current on the feedline will be proportional to how close the feedline length is to a quarter (or half) wavelength depending on whether the chassis of the transceiver/tuner/amplifier is floating/grounded. It is *imperative* that there be a high quality common mode choke on the feedline at the feed point of the antenna. "Ugly balun" or other random solenoid wound chokes are not reliable - see the work by K9YC, GM3SEK, etc. and select a choke that shows at least 5 K (preferably 10K) choking impedance on 80 and 40 meters to disconnect the outside of the coax shield from the antenna. > The microphone for the K3 is an Audio-Technica that works well > everywhere else. Assuming the Audio-Technica has an XLR connector, make *sure* the shield (pin 1) is *not* connected to the mic return (pin 7, pin 8) and depending on the age of your K3 make sure there is no RF choke between pin 7 or pin 8 and the circuit board ground. 73, ... Joe, W4TV On 11/22/2015 6:02 PM, Jan Ditzian wrote:
I have a problem that appears to be changing, but I could use some help. The problem is RFI in the audio input (microphone input) when I use my vertical antenna on 40 meters. Here is a rundown of what has happened: I have a 67-foot elevated vertical that I can use on 80 and 40, and it works fine on CW. However, on SSB, both bands, there clearly is feedback; there is no feedback on the other bands where I use a C3 yagi. Initially, the feedback was so bad that the rig would go into oscillation, and I had to turn the amp to standby. I recently purchased the new KSYN3A and decided to install it. I replaced the K3 with my IC-730 backup, using the hand microphone that came with the 730. The 730 did not have any RFI. I finished the modification and returned the K3 as the operating rig. Now, the RFI on 40 seems to have diminished substantially or disappeared, but it still happens on 75/80. However, it seems to be much less there as well. I do not suspect that the KSYN3A had anything to do with this, but perhaps I tightened connections better when I returned the rig to service. I also redid some ground connections. The microphone for the K3 is an Audio-Technica that works well everywhere else. It has a long cord, though. I put a few toroids on the cord near the microphone connector and that has possibly reduced RFI a little, but it is still there. Is there a possibility that a bypass capacitor is bad, or has someone else had the problem and solved it externally to the K3? For instance, has anyone found that a long string of ferrite beads has cured this problem? Despite decades of operating, I am hardly a troubleshooting hotshot, and I would appreciate guidance. Thank you, Jan, KX2A ______________________________________________________________ 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]
______________________________________________________________ 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]
