Antenna tuners have their place---just not in my shack. That said, your tuner is actually a band-pass filter whose performance as a filter is dependent on what it's matching.
If you really need a high-pass filter to correct an issue, then I think that you should use a purpose-built filter. Just my HO. Wes N7WS --- On Thu, 4/15/10, Al Lorona <[email protected]> wrote: > From: Al Lorona <[email protected]> > Subject: [Elecraft] [OT]: Antenna Tuners - one more reason > To: "Elecraft Reflector" <[email protected]> > Date: Thursday, April 15, 2010, 12:08 AM > There are many hams who dislike > antenna tuners and will go to great lengths to avoid having > to use one, including putting up multiple antennas, trimming > antennas inch by inch, and using elaborate matching schemes > involving transmission lines of various lengths and Zo. > > Besides the tremendous freedom a good antenna tuner gives > you with regard to the length of your antenna, length of > your feedline, type of feedline, and choice of operating > frequency, there is one other advantage that many often > forget and which I rarely hear explained. > > I use a homebrew link-coupled balanced tuner. It's getting > harder to find a commercially-built link-coupled unit, but > the most famous example is the good old Johnson Matchbox > which most folks are familiar with. > > Anyway, the advantage I'm talking about is that when > properly adjusted, a link-coupled tuner acts as a high-pass > filter. This means that it provides additional rejection of > AM broadcast stations in the 530 - 1710 kHz band. This > is really important to many hams, particularly when they > live close to one of these high-powered transmitters which > are always on and have plenty of potential for causing > problems in the receiver. > > I have run simulations of my particular tuner (which is not > exactly like a Johnson) which show that I enjoy a minimum of > -30 dB of rejection at 1710 kHz (the closest end of the > broadcast band and thus, the worst case) when I am tuned up > on 80 meters, and -50 dB when I'm tuned on 40 meters. I have > confirmed these numbers with measurements. > > I have troublemakers at 1110 and 1300 kHz, both 50 > kW only about 1.5 miles away. I believe they would cause > me some problems if I did not have this tuner in the line > which knocks them down by 42 and 38 dB, respectively, > when I am operating on 80 meters. When you knock down a 50 > kW signal by 40 dB, it looks like a mere 5 W signal! > > So the next time someone complains about "lossy tuners", or > having to "twirl dials", remind them that there is this > hidden benefit to using a good old-fashioned, > link-coupled tuner. > ______________________________________________________________ > 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 > ______________________________________________________________ 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
