> Let me throw a small monkey wrench into this. If you have an
> accurate set of measurements at the base of the antenna and a
> Smith chart program, you can achieve a wider bandwidth by NOT
> adjusting the L network to an SWR of 1:1 at a specific
> frequency. The trick is to set the SWR circle on the Smith
> chart to the max value desired and then to move the impedance
> plot until the greatest range of values are within the
> SWR circle. This will give you a "W" shaped SWR plot where no
> place is 1:1 but the maximum range is within the specified
> range of SWR.
>
> 73, Roger
Roger, you are absolutely correct and that is how I handle things here in
Idaho where I use CATV lines for runs over 100 feet. I set things up so that
there is a low loss matching network at the base of the antenna which
converts the impedance from the antenna input impedance to a nominal 75
ohms. The network is adjusted to keep the frequencies of interest inside of
a 4:1 SWR circle on the Smith Chart. That minimizes losses in the CATV line.
The final matching to the 50 ohms preferred by most transceivers (and some
amplifiers) is done at the station end.
That said I am exploring heuristically the use of a Tee network with series
coils and shunt capacitor as an alternative to the normal L network or
series capacitors and shunt coil Tee-network for matching at the station. I
tried one and found that in my particular situation it increased the 2:1
bandwidth compared to the bandwidth of an L-network doing the same matching.
It might be just plan coincidence but I am curious so am following up. I
suppose that I should also note that the L-C-L Tee-network is not the normal
one used in antenna tuners -- those are generally C-L-C.
It was good of you to add this clarification (not a monkey wrench at all).
73, Tod, KØTO
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