Jim Thomson wrote:
> Has anyone tried this b4 ? I have a F-12 340N, used, of recent vintage.
> OK... here's the deal. I'm seriously thinking of installing a Jennings
> ceramic 10-1050 pf @ 15 kv motor driven vac cap in series with the hot
> leg of the DE.
> On paper, after doing the math's... this should work... and result in a flat
> swr across the entire band. The stock swr curve is ok.... but I want to
> be able to operate at the opposite ends of the band. F-12 measures the swr
> curve in the shack, using the FT-1000MP's internal SWR meter.... and 400'
> of LMR-400 to the yagi. The real swr curve, measured at the DE, is of
> course, higher. [worse]
> Have any of you tried this b4.. or seen it done ? The idea was to tune the
> DE to the bottom of the band... or even a little lower. Then with 1050 pf
> dialed in.. [ 21.7 ohms Xc]..... swr should be flat at 7003 khz. As I
> move up the band, less pf required. .. [ more XC]
I did some antenna range tests with my MonstIR, varying the driven
element length while leaving the director and reflector fixed.
You can improve the SWR bandwidth doing this, but the gain and
F/B drop off as you get away from the optimum frequency
to which the parasitic elements are tuned. You really need to
tune all 3 elements as is done in the MonstIR.
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