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End fed wire antenna ... workable??

May 2nd 2018, 20:11

W0DBB

Joined: Nov 29th 2017, 18:15
Total Topics: 0
Total Posts: 0
Hello all-

I live in a 1070 11' x 40' trailer. Its roof is actually steel!

It runs almost due N / S.

South end I have a mast ~ 12' above roof and a Diamond X300 at top. All coax runs through window next to mast. Shack is just inside window.

I am thinking of a end fed wire at 10' above roof, fed from South end and running almost exactly down center of trailer all 40' length

I do not have room to run any type of radials.

Doing this and using a tuner will it work functionally on 10, 20, 40, 60 & 80 or am I just having a Prozac moment?

73,
Colin, w0dbb
May 3rd 2018, 08:48

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
A vertical is usually a better choice in your situation.

While the roof should be usable as the radial or counterpoise for an end fed wire, the short distance between the horizontal wire and the roof will make it hard to get acceptable performance. Also, if you are looking for DX it is likely that you don't have enough height--you typically want at least 35 feet above ground on 20 meters.

An electrically short efhw typically requires a good radial system or counterpoise for good efficiency. This is less important if you have a resonant half wave or multiple but you don't have that.

But, even a poor system may be usable on the digital mode FT8 or CW for making very short contacts.

Zak W1VT
ARRL Senior Lab Engineer
May 3rd 2018, 12:52

W0DBB

Joined: Nov 29th 2017, 18:15
Total Topics: 0
Total Posts: 0
My understanding is a vertical is lousy for DXing. Even as low and 12' above roof? What if, to get enough length, I run the wire around the top edge of the roof? Basically a long rectangle (sigh) could onle be 5 to 7 feet above roof?

I've seen a couple hams that run in their attics or not more than 12" above their roof. The've said not great but the've managed to WAS.

And, yes. Sunspots SUCK right now (sgh).

73,
Colin, w0dbb
May 3rd 2018, 14:09

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
A vertical is inferior to a high half wave dipole or Yagi aimed in the right direction, but you don't have that option. The biggest issues with verticals is local noise pickup and an inadequate radial system. You may find the metal roof to be usable as the counterpoise.

A large loop can work well for short distance contacts on the low bands but it won't have enough height to do better than a vertical using the roof as the counterpoise.

But, the only way to be sure is to put it up and try it out.

I was quite surprised with my 80 meter wire vertical hung in the trees. Not only was I able to work DX with 100 watts, but it only took me 3 months to collect all the QSLs I needed for 80M DXCC and finish my 5 Band DXCC!

Zak Lau W1VT
ARRL Senior Lab Engineer

Oct 1st 2018, 07:20

W1AAF

Joined: Nov 28th 2011, 17:38
Total Topics: 0
Total Posts: 0
Colin - While there are better choices, I think a base loaded vertical is the way to go in your situation. You will be able to cover the bands you mentioned, albeit without sufficient radials, it will favor the higher bands. An end fed for your situation will be a rather poor choice. In comparing an 85 ft end fed at 30 ft. to a 41 ft 40m vertical dipole, the vertical is the winner hands down. 73. Mark W1AAF

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