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Author Topic: antenna tuner for inverted L antenna 160m  (Read 6976 times)
1431
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Posts: 18




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« on: April 09, 2010, 05:23:22 AM »

i have an 500w transmitter (50ohm output) at 1431khz. my antenna is an inverted L. antenna's length is (5*(wave length))/16. 20m vertical and 45m horizontal wire. Do you have any idea for a working tuner to match my transmitter with antenna to have minimum SWR? i have a variable capacitor 500pf and a variable coil (50 turns at 6cm diameter). thank you
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KH6AQ
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Posts: 7769




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« Reply #1 on: April 09, 2010, 05:48:23 AM »

Modeled over perfect ground the input impedance at 1.431 MHz is 21 +j240 ohms. To tune out the 240 ohms of inductive reactance a series capacitance of 460 pF is required.

The resistive part of the input impedance will be 21 ohms or greater, depending on the ground system loss resistance.

A shunt inductance or capacitance from the feed point to ground can be used to match the antenna to 50 ohms. I haven't time right now to model that but will do so later unless someone posts the value.
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W8CCW
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Posts: 7




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« Reply #2 on: April 12, 2010, 09:59:54 AM »

EZNEC Model indicates 20.8 ohms + j239.2

TLW program (ARRL Antenna book)shows you will need 39.91 uH in series and 765.9 pf in Shunt.

Elsie program (Arrl Antenna book)the inductor you have (assume 12 cm long) has a max value of 60.2041 uH.

Therefore your capacitor is too small and your inductor is OK.

I note that you are doing your planning in the AM Broadcast Band. If you are really legal with this good luck. If you are plotting an illegal operation I hope you encounter the consequences.
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