Efhw antenna transformer build

[rogerjd]

I'm building a 49:1 transformer for an efhw 80-10. What size pf capacitor can I use? Or how large can it be? Currently I have
a few 1000pf at 20kv.

 

[prcguy]

Several sites say between 100 and 150pf but I think 100pf is better. I just assembled two more this week and am getting a little better match on 10m with 100pf over some 150s I was using in the past. The voltage rating is not that bad and you can get by with about 300v for a 100 watt transmitter and maybe 1kV for a 1500 watt transmitter when the transformer/antenna are used within the resonant bands. If you try and operate outside resonant bands then the voltage will increase and I would up the voltage another 4X in to be safe.

I'm building a 49:1 transformer for an efhw 80-10. What size pf capacitor can I use? Or how large can it be? Currently I have
a few 1000pf at 20kv.

 

[vagrant]

@prcguy - What is your source for the enclosure box and capacitors? I need to build a 49:1 or 56:1 for an 80-10 myself.

 

[prcguy]

I have a local electronics store for small boxes to fit a single FT-240, FT-140 or FT-114A size cores. Here is one I just put together with an FT-140-43 core that will handle about 150 watts with the small box I used. I usually use a small stainless steel wing nut for wire attachment but ran out, so this has a temporary brass thumb nut thing.



For higher power stacking two or three FT-240 size cores I use these boxes available from Homee Depot or Lowes. I think this was a Lowes box on this one. Notice the wire attachment with 12ga Teflon wire, removable link, thimble and cable crimp. Ummm, sexy.

Carlon 4 in. x 4 in. x 2 in. Gray Electrical PVC Junction Box (E989NNJ-5-HD) E989NNJ-5-HD - The Home Depot

Enjoy the Carlon Junction Box E989NNJ-CAR, gray designed to provide protection against external ice formation, falling dirt, hose-directed water and water entry during prolonged submersion from The Home

www.homedepot.com

For caps you might check eBay for dipped silver mica 100pf in 500 or 1kV depending on power. For two stacked cores use FT-240-61 and for three use FT-240-52.

@prcguy - What is your source for the enclosure box and capacitors? I need to build a 49:1 or 56:1 for an 80-10 myself.

 

[rogerjd]

Thanks for the input, but as they say
try it see what happens. So it's going up today