Raising OCFD dipole inverted Vee from 25’ to 35’

TexTAC

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I have a 40M off-center fed dipole hung as an inverted vee about 25’ up in a tree in my backyard with the ends about 8-10’ off the ground attached to my fence. It works pretty well and I have made contacts with Canada, Puerto Rico, Italy, Croatia, and Serbia on 40M and 20M. How much better will it perform if I can get the center up to 35’ or 40’ (I.e 10’-15’ higher). At that height, the center will be above my roof. On a percentage basis 10’-15’ is quite a bit higher than where it is now. Curious to know if the effort will pay off or not.
 
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prcguy

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It should work a little better all around, NVIS on the lower bands and DX on the higher bands. In my opinion, about 32ft completely horizontal is an ideal height for a wire antenna covering the 80 through 10m bands. The most gain straight upwards for NVIS on the lower bands is about 1/4 wavelength off the ground and 32ft is a 1/4 wavelength on 40m, which is about the highest band you will encounter NVIS in most cases.

Raising the antenna from 25ft to 32ft will give a slightly noticeable improvement on 80m NVIS and its also the first 1/2 wavelength point on 20m giving a low takeoff angle for DX. On 10m at 32ft you will be about a full wavelength off the ground giving a good low angle take off. My examples are for the entire antenna being at 32ft and lowering the ends down to 8 or 10ft will decrease efficiency on the lower bands and degrade takeoff angles on the higher bands.

Years ago I did a test with a bunch of people I talked with on a regular basis on a morning 80m net. I put up a modified military cross dipole that resonated on 40 and 80m and tested at the stock height of 15ft for the feedpoint/apex and at 30ft with the ends being low to the ground. On both 80 and 40m I went up in signal level about an S unit to most people, who were anywhere from 30 to 300mi away when raising the antenna from 15ft to 30ft. The radio was a Yaesu FT817 running about 5 watts and it put out a great signal with the full size crossed 80 and 40m dipoles.

I have a 40M off-center fed dipole hung as an inverted vee about 25’ up in a tree in my backyard with the ends about 8-10’ off the ground attached to my fence. It works pretty well and I have made contacts with Canada, Puerto Rico, Italy, Croatia, and Serbia on 40M and 20M. How much better will it perform if I can get the center up to 35’ or 40’ (I.e 10’-15’ higher). At that height, the center will be above my roof. On a percentage basis 10’-15’ is quite a bit higher than where it is now. Curious to know if the effort will pay off or not.
 

TexTAC

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I am going to give raising it up another shot this weekend, weather permitting. Raising it up initially to 25’ was relatively easy. Raising it any further is a real PITA. I’ve been using a weatherman multi tool as a weight to try and throw the line over the right branch. It got stuck a few days ago and it took me a few days to get it back down. Also snaking the antenna wire on both ends through branches so it is straight and not touching anything takes some skill.
 

K6GBW

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Getting your wire high is the universal pain all HF amateurs share! I've found that a 23' painters pole with a homemade hook on the end saves a lot of climbing. I simply tied a largish nut to the end of some paracord, attached it to the hook and pushed it up over the highest branch I could reach. If you can use a medium step ladder you would be able to do 30-35' pretty easy.
 

prcguy

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I'll be in TexTAC's neighborhood early August if he needs any help raising the antenna. Texas Towers up the street from HRO has push up masts in stock and they are great for getting the ends up as high as the center.

I am going to give raising it up another shot this weekend, weather permitting. Raising it up initially to 25’ was relatively easy. Raising it any further is a real PITA. I’ve been using a weatherman multi tool as a weight to try and throw the line over the right branch. It got stuck a few days ago and it took me a few days to get it back down. Also snaking the antenna wire on both ends through branches so it is straight and not touching anything takes some skill.
 

TexTAC

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Thanks but I want to get this done this weekend if possible! I also need to check out Texas Towers to see what they have, but I am thinking hiding it in a tree may be better for a bit until I get a better idea for a more permanent solution.
 

K6GBW

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Did you get it raised? I'm betting 40m won't be any different, but 20m and up you might see an improvement.
 

TexTAC

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I gave up raising the middle any higher in the tree after a few days of failed attempts and getting items stuck in the tree. However, I did raise both ends from 8 feet to about 15 feet. That made a huge difference! I made contacts on SSB with Russia, Spain, Brazil & and Costa Rica tonight. Almost made contacts with Denmark & Ireland but couldn’t make it through the pile-ups. I actually like the way it is strung up now because it is in a straight line and touches absolutely no branches. This will keep me happy until I decide what to upgrade.

Edited to add : Also upgraded the center and both ends with small pulleys to make it easier to maintain and added bungie cords at the tie offs to reduce wind strain. Also weatherproofed all connections.

Edited again to add: noticed a slight improvement in SWR before using the tuner. And yes, 20 meters appeared to be much better TX and RX as all my international contacts where there tonight.
 
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K6GBW

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Excellent! It's always the small victories! HF is residential areas is always a challenge. The guys with huge trees have no idea how good they have it. I've been fortunate in that my neighbors haven't said anything when I put up a small tower and mast combo. But there's always the competing interests of height vs. visual impact and then there's the XYL factor to consider. For me, I've made a bit of a hobby out of trying to find low impact antennas that will actually work. That said, the best antenna in the world doesn't work well when it's low. I've found thirty feet to be kind of a benchmark number. At that height 80 and 40 are pretty much local/regional and twenty and up start to get some good distance. But I have fun with it!
 
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