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

[Wes Stewart]

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 <alorona at sbcglobal.net> wrote:

> From: Al Lorona <alorona at sbcglobal.net>
> Subject: [Elecraft] [OT]: Antenna Tuners - one more reason
> To: "Elecraft Reflector" <elecraft at mailman.qth.net>
> 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.
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