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EFHW 134' Wire antenna and metal

I have a EFHW antenna that seems to be working pretty well at my house. I have a small parcel of land in the city and have maxed out the possible use of the land with an inverted V configuration. I made my own antenna mast out of steel chain link fence top rails and some other goodies for guy wires.

It does not seem like the conductive nature of the mast is effecting my antenna much or at all. It is hanging on an plastic isolation loop. Just curious if anybody has any input on this, I did my own research before I erected the antenna and it has worked accordingly. Debating if its worth pulling it down to wrap the top few feet of the antenna in something insulated. I am being spotted sometimes up to 3000 miles away using CW on 10 Watts. Any input or thoughts would be appreciated.

Also weather is breaking in the big mountains here soon and the 10 pointers are going to be getting activated daily =]

https://owenduffy.net/blog/?p=5520 Edit: ignore. I misread the op and thought he had made his antenna from steel wire. Doh.

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I assume the bottom of the mast goes straight into the ground? If this is the case and the antenna wire is close to the top of the mast then effectively you have created an earth (ground) close to the antenna.

You could insulate the bottom of the mast (and the guys) for example if the mast has four legs concrete them into plastic buckets sunk into the ground or if that is impracticable try and fit something like a fibreglass tube to the top of the mast to get the antenna as far away from it as possible.

Maybe not. The metal mast acts like a waveguide (a transmission line). A direct coupling or a capacitive coupling to ground brings a low impedance to the bottom of the mast. The mast as a transmission line transforms this impedance to the upper end. Transformation depends on length / Lambda. If this ratio is 1/4 or 3/4 or 5/4 or … then you have a high impedance at the upper end. In case of 1/2 or 2/2 or 3/2 or … then you have the same impedance like down. In case of other ratios values between.

So for a constant length of the mast the effect depends on the working frequency.

Maybe you have a low impact on some bands and a high on others.

73 Ludwig

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Hi,

Metinks you worry too much. I have used a steel tower for 50 years to support a range of antennas, including wires for HF. There is usually a stainless steel cable about 0.3 m long connecting to a good antenna insulator that in turn supports the wire. The cable is held 0.3 m clear of the tower for mechanical reasons by an aluminum tube.

There may be a teensy weensy part of a pF capacitance between the wire and the tower. So what? Insulating the wire would make that bigger,

Because all of my wires have been sloping there will be a little current induced in the mast. So the mast will both radiate a titch and adsorb some small amount of power. A fraction of a dB degradation is my estimate. That’s part of the cost of doing business.

Follow standard practice. A steel mast in concrete will provide for static discharge in the event of nearby storms. Insulating the mast serves no good purpose unless you want to use it as a radiator.

73
Ron
VK3AFW

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Rob,

I wouldn’t worry too much about this setup. Many hams are using antenna masts made of conductive material, having wires sloping in every direction.
The conductive mast will affect the radiation pattern of the antenna in some way. But keep in mind there are other objects affecting your antenna, too.
Especially if you’re operating from a small lot. Most likely, there are buildings in the vicinity of the antenna with tons of conducting material, such as lightning rods or rain pipes. They don’t have to be connected to your antenna. RF is simply coupling into them.
Depending on size and orientation, their impact on your antenna system can even be bigger than the one of the mast.
So I would say use it as it is and try to gain experience what’s possible with this antenna.

73, Roman

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Rob,

A run on the EZNEC simulation program shows no difference with or without the mast. Resolution 0.01 dB for azimuth and elevation patterns…This is in accord with my experience.

Input:
134 ft end fed inverted vee wire.
Ends at 10 ft agl
Mast 30 ft, tube 2 inch dia with antenna at the top 1 inch spaced away…Grounded.
Average ground
Test freq 3.600 MHz

I chose 3.6 MHz as the wire to mast spacing is smallest in terms of wavelength so coupling would be higher.

Now there are plenty of mast-antenna arrangements where the mast is bad or good. But they are other matters.

Th bottom line Rob is that your arrangement is OK.

73
Ron
VK3AFW

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Thank you so much for taking time to do this. I modified my antenna yesterday to add some fiberglass and it made absolutely no difference getting the wire 15 feet from the mast.

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Thank you so much, I agree. I was thinking about this yesterday and against my better judgment did modify the antenna and wasted most of my day. It made absolutely no difference.

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You are welcome

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Rob,

I saw your backyard antenna in your video. That thing is a beast, but should endure through MT winters no problem. Same as you, I’m trying to make CW QSOs from my KX2 in the yard on a SOTABeams dipole. I can hear people fine and being spotted as far away as Connecticut. Only QSOs were with the local CW class using the HT to coordinate freqs, etc.

Planning to try for real this weekend on a SOTA.

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Matt,

Thanks for taking time to watch my video! Yeah I am really pumped on the antenna it is working great. 10 watts on a night the bands are good will get me as far as South Africa with it. What are you going to activate this weekend? My wife and I are also getting out for an activation this weekend, we want to get a 10 pointed in MT or WY but think there is still just a little bit to much snow up that high. Not quite sure where we will go but it should be fun. That SotaBeam dipole is such an awesome antenna, I want one but the stock is out on DX engineering. I do have a center fed dipole from chameleon I use for QRP. Would love to CW S2S if it worked out!