Hi Nick, RX SHFT is normally used to cancel the effects of AM detection of very strong signals that blow by the mixer and enter the detector - overload. Since enabling RX SHFT cured this 60Hz+harmonics problem, it seems likely that you were copying a strong signal with little or no modulation. You may have been hearing the transmitter's power supply ripple.
Is your QTH near a broadcast station or military facility? I've come across a similar problem once in a while when operating portable. Usually, the signal comes out as station audio that can't be tuned away from. A couple years ago, I had exactly the same symptoms (never could explain the _what_ part) and RX SHFT was what I used to solve it. It also works well on the OM down the street that operates with all gain controls set to 11. :) 73, matt W6NIA On Sun, 9 Feb 2014 17:06:13 -0800, you wrote: >Hi all, > >I'm trying to make sure that I understand something kind of weird that I >ran across today; I hate resolving a problem without fully appreciating >everything that was causing it. > >Since 10M was pretty active today, I thought I'd pop on, and since the >ground was nice and wet, I thought I'd give my "Home Depot" ground-mounted >vertical a go. (It's a vertical made entirely out of things you'd find in >Home Depot's plumbing, lumber, and window departments. I didn't have the >tape-measure radials connected today, just the ground stakes around it.) > >Midway through the day I started picking up what looked and sounded like a >60Hz + harmonics buzz. I did not have a power supply connected to the KX3, >and I pulled all the other connectors from the computer to make sure I >wasn't getting some kind of ground loop hum. No dice. > >To make matters more interesting if I backed the antenna connector halfway >off, such that the ground was no longer connected, the hum disappeared. I >started worrying that I was having some trouble with the local utility, but >decided I'd better rule out something in the house first. > >Through the course of troubleshooting, I came to find the culprit was a USB >phone charger on the other side of the wall from the antenna, with the USB >cable stretched out across the floor. Unplugging it or disconnecting the >USB cable mostly made the noise go away (but not entirely, though there are >so many different power supplies and things inside the house, there could >be multiple sources of noise, too). > >I mostly sorted the problem by winding the proximal end of the USB cable >about 6 times through a ferrite core, though a small amount of noise >remained just by virtue of the thing being plugged in at all. > >Then I noticed that tuning up or down a few Hz had no effect at all on >where the noise showed up in the waterfall, which got me wondering if it >was a noise getting picked up in decoding. I set the RX SHFT setting to >8.0, and indeed, the noise disappeared entirely. > >I don't completely understand the "why" part of what happened here... that >is to say, why did it change based on whether the ground side of the >antenna was connected or not, and why did changing the RX SHFT get rid of >it? > >(?Also I note that the ground is particularly wet and conductive today, >which may or may not be a factor in why I noticed it today.) > >Any thoughts? > > Nick? ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
