Author Topic: End Fed Half Wave antenna coupler  (Read 7313 times)

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Lamewolf

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Re: End Fed Half Wave antenna coupler
« Reply #15 on: March 15, 2016, 03:37:03 PM »
Here's an end fed half wave coupler I built for 60 meters, with the variable cap I used and the T130-2 core and #18 insulated wire on the core it easily handles 100 watts.
It feeds an 88' sloper that has the feed point about 7 feet high and the far end at about 50'  With the cap set for lowest swr on channel 3, it covers all 5 channels at less than 1.5:1 !
« Last Edit: March 15, 2016, 03:39:13 PM by Lamewolf »

Lamewolf

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Re: End Fed Half Wave antenna coupler
« Reply #16 on: April 15, 2016, 12:29:32 PM »
Also understand, that an End-feed 1/2 wave will approach Infinite Impedance at it's Resonant Frequency.... and that makes designing an AUTO-Tune Antenna Tuner for that specific situation, as real BEAR.....

Actually, the impedance of an end fed half wave is around 3K to 5K ohms and can be matched with a simple L network with a series inductor and shunt capacitor on the output which is what most auto tuners are.  The problem is not that its hard to match that impedance range, its the fact that the EFHW is a voltage fed antenna which means there are high voltages present at the feed point which can cause arching if the tuner components aren't robust enough, it could cause damage to the tuner.

spacecase0

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Re: End Fed Half Wave antenna coupler
« Reply #17 on: April 15, 2016, 11:03:37 PM »
Actually, the impedance of an end fed half wave is around 3K to 5K ohms and can be matched with a simple L network with a series inductor and shunt capacitor on the output which is what most auto tuners are.  The problem is not that its hard to match that impedance range, its the fact that the EFHW is a voltage fed antenna which means there are high voltages present at the feed point which can cause arching if the tuner components aren't robust enough, it could cause damage to the tuner.
I find it quite odd that something infinite in the math turns out to be pretty easy to achieve in the hardware
I avoided 1/2 wave end fed antennas for years over the issue
but it turns out they are quite amazing despite the math reservations