[Elecraft] Tuners and spurious responses

[Al Lorona]

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