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Author Topic: "NG9D INVERTED DOG FENCE" ANTENNA  (Read 6436 times)
NG9D
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Posts: 10




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« on: February 06, 2007, 11:22:19 AM »

I have been using a 135 ft inverted-L for about a year made using the kind of wire sold for "invisible" buried dog fences. It is 20 ga. solid copper covered in a UV resistant tough HDPE insulation material. The wire is light, durable and when thrown over tree branches it is self supporting and insulated. It is so small in diameter and since HDPE has low coefficient of friction, ice and snow don't seem to stick to it.

I knotted the wire itself and tied a nylon cord and counterweight to the far end. Three trees support my antenna and the longest unsupported leg is about 60 ft + about 15 ft of nylon cord to reach the far tree.

End fed against a city water pipe ground from my basement with MFJ 941C tuner allows me to use it as 1/4 wave on 160, 1/2 wave on 80 and full wave on 40M. It also works well on 20m (30m works well, tuning is touchier). The copper water pipe ground is several feet from my station, and I believe the antenna works well, in part, due to this grounding connection.

The antenna works pretty well with my Ten Tec Tkit QRP rigs on 80m, 40m,30m and 20m.  I have found it does better than my 1/4 wave coax fed marconi / vertical antennas on all bands roughly 80% of the time.

I bought 500 ft spools of this for about $25, so material cost is ~ 5 cents per foot.  Total price of the antenna (w/o tuner) is $6.75.  Feedline is the antenna itself.  Entry through basement window involved adding a strip of vinyl electrical tape at possible wear points, however no wear is apparent.

Almost forgot to mention, due to small diameter it is very difficult to see once up in the air. I live in an antenna restricted community but nobody has complained about my "inverted dog fence" antenna.

73, NG9D
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ONAIR
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Posts: 3570




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« Reply #1 on: February 07, 2007, 12:44:48 AM »

     Wow, that's great!  Do you think that stuff would work hidden inside an actual vinyl fence around the perimeter of a property?
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NG9D
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Posts: 10




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« Reply #2 on: February 07, 2007, 05:25:51 AM »

"ONAIR":

I have a friend who uses a very low antenna supported by a fence in his yard and it works for him on 80m.  Great for local contacts, with the ground reflection, its somewhat of a cloud-warmer I think.

My particular inverted-L has a vertical leg about 35 feet high.  I've tried different configurations and have found that generally more vertical height improves this type of end-fed antenna.

This one is in an inverted-L arrangement with the top fairly horizontal and top leg bent in plan-view.  

I also had really good luck with a 165' end fed inverted-V with the apex at about 45 ft (the V inclined somewhat, and non-symmetrical; the last leg of the V being about 75').  Also fed against copper water pipe ground using tuner.  This has been my best try so far compared to my quarter wave verticals.

I say experiment!  Try your vinyl fence antenna support, use insulated wire and run low power if people are around it.  Let me know how it works!  

73
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WA7IRY
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Posts: 63




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« Reply #3 on: February 08, 2007, 10:20:04 PM »

Can you tell us what type of store you were able to find this type of wire?  Home improvement-type, pet store, or ??

Thanks,
-- Rod  WA7IRY
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NG9D
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« Reply #4 on: February 12, 2007, 10:37:41 AM »

Menard's, in the pet dept.  Last year, I had to wait until spring for them to re-stock.
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KB1JCY
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« Reply #5 on: March 15, 2007, 07:09:30 AM »

Can I run 100 W on this type of antenna?
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NG9D
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Posts: 10




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« Reply #6 on: April 04, 2007, 06:19:27 AM »

I use it from QRP to about 80W output.  As long as your tuner can handle 100W of RF the 20 ga. solid copper wire should do fine.  

By the way, dog chewed counterweight/nylon cord off of the far end.  Since antenna dropped to ground level, I inspected the HDPE insulation covering.  The color is fading but no apparent cracking.  So I am experimenting with new configuration.  Now the antenna is more of an inverted-U than and inverted-L, with the far end tied to a fence.  It still works at QRP level power.  I think the reason it works is 1) good ground connection close to ATU feed, 2) good soil conductivity, 3) ample vertical height from feed point.  I am also thinking that the performance of the inverted-U configuration could be related to the amount of area enclosed by (unterminated) "half-loop".

Next, I will add 30' to increase length from 135 to 165' so it will be 5/8 wavelength on 80m and 5/4 on 40m.  I've used 165' in an inverted-L configuration of sorts in the past with apex at about 40ft fed against city copper water pipe ground and it worked great!
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