[Elecraft] [OT]: Antenna Tuners - one more reason

[Al Lorona]

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.