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I recently picked up an Icom M802 marine HF radio that includes ham bands and an Icom AT-140 antenna tuner. I have a ham license, but have been away from HF for many years and have never used a random wire antenna before.

Ultimately I may want this on my boat for WX data, GRIBs, email and so on, but before doing that I want to get it running at home and experiment with some data over HF. I need an antenna and don't want to spend much on a pricy indoor loop or the like, and I don't have an attic. I live on a small lot with an HOA and based upon the layout it's best physically to use an end fed long / random wire. I would like to operate on 80 to 10 meters, although I'm not sure I have enough space for that.

The house is on a slab and all the plumbing is plastic. The radio needs to go on the second floor. Fortunately there is a window that leads out to a roof and I can put a mounting hook into the side of the house. I can also mount the tuner there (it's designed for outdoor mounting). This would give me 20 or more feet above ground.

The tuner has a screw lug to connect the end of the long wire, but I'm concerned about connecting the wire directly to the tuner. I don't know how strong that lug is.

The tuner manual says to avoid multiples of half wavelength as the radiating element, and says if I use a 15 meter wire I can operate all marine bands from 1.6 MHZ to 25 MHz. Further, consulting this link is helpful:

https://udel.edu/~mm/ham/randomWire/

This would rule out a 49 foot 2.5 inch (15m) length due to wanting to use 80 meters but allow 71 feet, although I may not have enough space. I could do 40 feet for sure. If I do 40 feet I can go between two points on the house (preferable because the house won't swing in the wind) but for 71 feet I would need to go to a tree on someone else's property (which I can do if need be).

My questions are:

Can I string the wire between two mounting points and use another, shorter wire from the tuner to the antenna wire? It could be very short, like a foot or so.

If the end of the antenna has to go directly to the tuner, I'm concerned about a strain relief so the tuner mount point is not damaged. That's why I asked the above question. Is there a better approach?

How do I do a ground or centerpoise? The tuner is supposed to be grounded, so do I put a ground rod into the dirt and run a wire down to it? Would that be a centerpoise?

Can I use the ground lug of an electrical outlet as a counterpoise?

Can I use a wire shorter than 71 feet for 80 meters effectively? The tuner manual seems to imply that I can use antennas less than 1/4 wavelength in length.

What type and gauge of wire is best to use for the antenna? Can it be insulated to prevent rust?

I know this is asking a lot, sorry, but I would greatly appreciate the help, thanks!!

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4 Answers 4

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Jim, This is a small program to output possible non-harmonic wire lengths.

bands_contest   = [3.65,7.025,14.025,21.025,28.025]
bands_warc      = [3.65,7.025,10.115,14.025,18.080,21.025,24.900,28.025]
All_Bands={'Contest':bands_contest,
           'HFAll':bands_warc}

def f_to_m(f:float)->float:
    return 299.792458/f


for bName in All_Bands.keys():
    print(f"Non Resenant for {bName}")
    band_length_in_m=[f_to_m(b) for b in All_Bands[bName]]


    wire=5.0
    while (wire<20.0):
        NonRes=True
        for b in band_length_in_m:
            fraction=b/wire%1.0
            #print(f"wire {wire:4.1f} {b} {fraction:5.2f}")
            if (fraction > 0.4) and (fraction < 0.6):
                NonRes=False
                break
        if NonRes==True:
            print(f"wire {wire:5.2f} Possible")
        wire+=0.10

When you run it - it would produce

Non Resonant for Contest bands

 5.10m Possible
 5.20m Possible
 5.40m Possible
 6.30m Possible
 6.40m Possible
 8.00m Possible
 8.10m Possible
 8.20m Possible
10.20m Possible
10.30m Possible
10.40m Possible
10.50m Possible
10.60m Possible
10.70m Possible
10.80m Possible
11.10m Possible
11.20m Possible
11.30m Possible
11.40m Possible
11.50m Possible
11.60m Possible
11.70m Possible
11.80m Possible
12.90m Possible
13.00m Possible
13.10m Possible
13.20m Possible
13.30m Possible
15.30m Possible
15.40m Possible
15.50m Possible
15.60m Possible
15.70m Possible
15.80m Possible
15.90m Possible
16.00m Possible
16.10m Possible
16.20m Possible
16.30m Possible
16.40m Possible
17.80m Possible

Non Resonant for HFAll bands

 5.10m Possible
 5.20m Possible
 6.30m Possible
10.20m Possible
10.30m Possible
12.90m Possible
13.00m Possible
13.10m Possible
13.20m Possible
13.30m Possible
15.30m Possible
15.40m Possible
15.50m Possible
15.60m Possible
15.70m Possible
15.80m Possible
15.90m Possible
16.00m Possible
16.10m Possible
16.20m Possible
16.30m Possible
16.40m Possible
17.80m Possible

Things to note:

  • The Freqs I used are centered on the CW Sections.
  • The wire length has not been adjusted for a velocity factor
  • I did not include 5Mhz

Start at the longest ... trim shorter....

Hope that helps - you could double check a possible length using MMANA/4NEC2 etc.

73s - Tim

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You need a 9:1 unun.

I use one of these Matchboxes:

http://earchi.org/proj_homebrew.html

It has provision for a counterpoise but if you use 6' of coax to connect it to the tuner the braid acts as a counterpoise.

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Jim.

Many of the details you are asking about for a long wire antenna are not critical.

Generally, the longer and higher a long wire antenna is, the better it will work.

Any long wire of any construction and length will work to some degree. How well it works depends on a variety of factors related to the length of the antenna compared to the frequency of operation and the height.

Often the construction and length depend mostly on the specifics of the installation site such as availability of mounting points and available space, rather than an exact design.

Any antenna will work for receive, however for transmit the antenna system impedance needs to match that of the radio, otherwise you risk damaging your radio when transmitting. So long as your tuner can be adjusted for a good match, this isn't a problem.

The type of wire makes very little or no noticeable difference at all at HF frequencies, so you can use anything so long as it can support it's own weight. Plastic covering on wire used for a long wire antenna makes no difference. One exception is that you need wire that won't rust or corrode for obvious reasons.

In your case i would forget about the counterpoise idea, just connect the end of the antenna to the tuner and earth the antenna tuner to ground. It's a very bad idea to use power outlets for grounding.

My advice is rather than to take the approach of a specific design, string up an antenna as best you can according to your particular surroundings, make sure you adjust the tuner for an SWR of less than 2:1, and you will find that the antenna will probably work in a satisfactory manner.

Hope that helps !

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Jim, some more input.

Can I string the wire between two mounting points and use another, shorter wire from the tuner to the antenna wire? It could be very short, like a foot or so.

Yes this will work. And it will not really effect the signal as long as the mounting points are not metal/conductive.

If the end of the antenna has to go directly to the tuner, I'm concerned about a strain relief so the tuner mount point is not damaged. That's why I asked the above question. Is there a better approach?

strain relief/Spring/Counter weight... all are valid options.

How do I do a ground or centerpoise? The tuner is supposed to be grounded, so do I put a ground rod into the dirt and run a wire down to it? Would that be a centerpoise?

I would go and stick as many copper rods in the ground as close to the AT-140. And grounds the AT-140 to that.

Can I use the ground lug of an electrical outlet as a counterpoise?

err, NO. This is not a good practice. You will get more trouble from domestic appliances - and you will possibly cause trouble for your domestic appliances also.

Can I use a wire shorter than 71 feet for 80 meters effectively? The tuner manual seems to imply that I can use antennas less than 1/4 wavelength in length.

see previous data

What type and gauge of wire is best to use for the antenna? Can it be insulated to prevent rust?

If you are in an HOA then stealthy is the way to go. #14 is very difficult to see, and if you got a green colored sheath (assuming you have trees around) I think it would blend even more. Copper wire does not really rust. Try and avoid solid-core wire, as it tends to fatigue.

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