I have a 50 kW BC station in line of sight with my antenna. When I used a vertical antenna without a tuner, it was enough to overpower the bias in the K3’s T/R switch and generate spurs all over 40 and 30 meters. I fixed it with a highpass filter before changing to a horizontal antenna . When I rotate my dipole, there is a point where one end gets close to a structure. The tuning changes, so I know it has an effect, which must unbalance the system. Maybe coincidentally and maybe not, local noise increases at that point. I think I will try isolating the tuner from ground and feeding it through a balun.
Victor 4X6GP > On 22 Dec 2018, at 9:05, Al Lorona <[email protected]> wrote: > > Vic, it may well be your imagination (!) but you may also be hearing the > rejection that your tuner gives you, particularly to strong AM stations in > the broadcast band. My measurements, as well as circuit simulation, show > about a 40 dB rejection of AM stations when the tuner is tuned to 40 meters. > > Circuit simulation of the Johnson circuit shows not all that high a Q, but it > certainly is starting to look like a broad bandpass response. (It's actually > more high-pass than band-pass.) That's why it's effective against the > broadcast band. It's yet another argument to use a tuner like that one. > > Interestingly, I just moved from a link-coupled tuner back to an unbalanced > tuner with balun because my measurements of common-mode current on the > transmission line show that the balun is more effective at suppressing it. > The link-coupled tuner acts more like a voltage balun which would be okay if > the antenna were inherently balanced, but in many cases the current balun > suppresses common-mode better when the antenna is in an environment that > makes it not well-balanced. When power lines or houses or cars or other > things are in the antenna's near field it tends to make the antenna present > an unbalanced load to the transmission line. That's when equal currents (not > voltages) work better. But I'm repeating what has long been known. > > If you can measure this stuff, like with an RF current meter, it becomes much > clearer. > > Enjoy your new, cleaner reception, thanks to that tuner! > > Al W6LX > > >>>> This may be totally imaginary, >>>> -- >>>> 73, >>>> Victor, 4X6GP > ______________________________________________________________ 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]
