End-Fed Antenna, 10/80 meter.

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Denis Gagnon:
Can it lay flat on the beams in my attic?
Will it be dangerous for fire? I only run 100 watts.
Or should I just lay it flat on the roof?
I live in a fourplex and no room for outside antennas at all.
Thanks for the input on the subject.
Denis
VE6AGE

Alex:
If you have to lay it on something I would get some Teflon wire the closest color to your shingles and weave it over your roof.


Alex...

John Cunliffe:
Well, don't lay it on the roof because every time it rains or snows it will be detuned by quite a bit.
Get a few 4-5 inch pieces of 1/2 inch pvc pipe and use them as stand offs from your beams. Try to use one as a end insulator and get the end away from anything flammable.
Even with 100W the voltage on the end of your wire can be several 1000V and if the humidity is right and flammable materials around it can arc and cause a fire. It does not take much.


John

Robert VanTichelt:
If I can remember correctly a 1/2 wave end feed antnena has about 2000v-2200v on the end with 1kw applied. At 100 watts I would just use insulated wire. Most insulated house wire is rated at 600v. And, it will detune if it rains or snows weather it is inside outside, on the roof, 6" above the roof etc. I have gone the attic route, then on the shingles, then 5' above the roof, then 16' above the roof. You will receive signals. You will also receive RFI from the house. You will also transmit RFI to the house.

What I would personally do it try and use a thin, stealth wire thrown up into a tree, or supported outside some how. Use a small tuner or auto tuner at the end of the wire against a ground. This is the perfect place for one of the PAR 1/2 wave end feed antennas or the MJF end feed tuner and a wind sock pole if you have no trees. But, the further away from the building the better, especially a 4 plex.

I also wouldn't try and cover 10-80. I would try and set my self up with maybe 20 and 40 meters right now.

Steve Katz:
Actually, the end ("tip") of an antenna can develop several kilovolts of RF.  In theory, in "free space," the terminating impedance of a piece of wire just hanging in the air would be infinity, yielding "infinity volts" there.  In reality, 5000 Ohms or more is not unusual.

At 5K Ohms, the voltage with 1500W power applied would be 2738Vrms, >3.8kVpk .  With 100W it's 707Vrms, 1 kVpk.  The "600V" insulation on common wire isn't sufficient, especially at radio frequencies.

That's why we use end insulators.  I'd keep the HV points far away as possible from anything combustible.  Unfortunately, a 1/2-wave end fed (or 1-wave, or 1.5 wave, or 2.0 wave, etc.) has a feedpoint voltage that's just as high as the element tip voltage, which is a great reason to never use that length if you're end-feeding an antenna.

WB2WIK/6

 

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