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1-8 of 8 messages
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Inverted Vee
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by KC0LET on August 20, 2002
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I finally got permission from my parents to put up an inverted vee antenna. I have a 60' freestanding homebrew tower I going to use for a center support. I was advised to cut a dipole 88' long and feed it with ladderline and use a tuner, but I don't think you can run ladderline down the side of the tower without ill effects.
What would happen if I was to cut dipole for all the bands I plan to operate (80m - 10m) and connect them all to a 1:1 balun, in effect making a fan dipole? Could I do this and not have to use a tuner? I thought since I am new to HF it would be more convient not to have to use a tuner.
Thanks, Evan KC0LET
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RE: Inverted Vee
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by AC5E on August 20, 2002
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Hi Evan: First, 88 feet is "resonant nowhere," at least nowhere of any great interest. If you want an antenna you won't have to use a tuner on you will need a resonant antenna; and both the included angle and the height above ground (the real conductive layers of the earth, not the surface) will be critical.
Ladder line won't do, since you will have a major mismatch at the feedpoint. Personally, I would use a quality RG8/RG213 coax, and make sure it does not flop in the wind. Remember to leave a drip loop where it enters the shack, also.
Next, the usual formula for a half wave antenna is 468 divided by the frequency in mHz. That figures out to be 133.7 feet for the bottom of 80 Meters: 65.5 feet for the middle of 40 Meters; just under 33 feet for 20, etc..
You can tie several wires together at a common feedpoint. The formula is reasonably close if the wires are well separated, but the closet they get the less accurate the calculated result becomes. (Hint: cut them long, and trim them after the antenna is up.)
If the wires are parallel and only a few inches apart the result is part antenna and part transmission line and the wires for the higher bands will be much too short.
Personally - I would install a commercial multi-wire trap dipole such as an Alpha Delta DX-CC or a similar antenna as a baseline antenna, and then build and try several other designs to get a feel for how antennas work.
73 Pete Allen AC5E
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RE: Inverted Vee
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by W7WIK on August 20, 2002
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Evan,
You can do either with good results.
If you use ladder line or TV twin-lead, make sure it's well supported at the feed point and mounted in such a way that it stays away from anything metal like your tower, rain gutters, etc... 6 or more inches will do. Unlike coax, ladder line will react to the environment it's close to. Don't let it lie on the ground. Make sure your tuner has a balanced output. Sometimes it's more practical to run a short length of coax to just outside the shack into a 4:1 balun and attach the ladder line there. You'll have a multi-band antenna with a very low-loss feed line. Ladder line or TV twin-lead has much less loss than ANY coax. You will need a tuner.
Now for the fan inverted vee. I had one and it worked great. Four, or maybe five bands and it works good. any more and I don't know... don't have the experience and don't really think it would work well. Pick your 4 or 5 favorite bands and go for it. Don't let the angle of the elements come closer than 90 degrees or so (the two for each band) and space as evenly as possible. Make sure the elements are set opposite each-other for each band. Cut for the standard 468/MHz. Start with the longest pair and tune them first, next longest and so on. In my experience, don't cut the lowest/longest band pair all the way down until the rest are close. Take your time and experiment a little. Carefully cut them a little at a time. Sometimes the elements will be a little uneven which is influenced by the environment. Easiest to use an antenna analyzer like an MFJ-259. No tuner needed for this one unless you use it on non-resonant bands.
Good luck,
Marco, W7WIK
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RE: Inverted Vee
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by NB6Z on August 21, 2002
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Evan,
88 feet with open feed line (twin lead) would make a great 20 meter EDZep wire if it were NOT inverted. You will still be able to tune it for good results on 40 thru 10 meters if you invert the wire. Keep the feed line off-set away from the tower by at least 3 inches and you will not have any issue with the line. A Fan dipole for all bands is possible but it is a pain to adjust! Go here to find more ideas on HF wires like fan dipoles and EDZeps.
http://home.teleport.com/~nb6z/nb6zep.htm
If some day the folks let you put a beam on that tower, lookup the "ZL Special" antenna. All you need is TV twin lead, 2X4 wood and bambo to make a nice working rotatalbe mono bander.
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RE: Inverted Vee
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by KC0LET on August 21, 2002
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I looked at the Alpha Delta DX CC and it looks to be perfect for my application. The only thing is, AES told me it did not require a tuner, while HRO told me it did require a tuner. Which is true? It sounds like Pete has some experiance with these antenneas, maybe he can answer this.
Thanks, Evan
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RE: Inverted Vee
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by K8ZO on August 21, 2002
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I am not an antenna expert. What I do know is that I has 80m length dipole mounted 18 inches off of a tower leg using a wooded 2x2, some more 2x2's down the side of the tower holding 450 ladder line away from the tower. It "worked". It seemed to work as well as my friends systems which were usually coax fed dipoles or G5RV's. I could load it easily on 10 through 80. 160 would not load easily. "Loading" required the use of a tuner with twin lead output.
Dick
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RE: Inverted Vee
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by N0HR on August 22, 2002
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Evan
Congrats on making it this far... I hope to work you one of these days (make sure to try eventually every band and mode at various times and under various propagation conditions). I was 12 when I got my license (in 1980) but was fortunate to have a ham/father (KØGVG) - so I was't faced with your problem.
To answer your question (tuner or no tuner) - simply check out the on-line manual for that antenna: http://www.alphadeltacom.com/dxcc_ii.htm
Basically, lower-band dipoles (ie 40m/80m/160m) that are electrically shortened will have relatively narrow bandwidth. In other words, if you make a short dipole (using traps) for say 3.6 MHz - it'll do just fine at that exact frequency (and even +/- say 100 Hz). But if you tried to use it at say 3.9 MHz, it might be up to >5:1 SWR. A tuner comes in handy in such cases.
Longer dipoles (for the same band - and without traps) are "broader" (not as narrow banded).
If you install it (with some standoff from your tower) and it's really in the free and clear (not along side a big metal shed for example), my guess is that the antenna would be fine and only require a tuner for 80 meters and the extreme ends of 40m.
I hope this helps es 73,
Pat NØHR
http://www.n0hr.com
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RE: Inverted Vee
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by KG6AMW on August 23, 2002
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I own one of these antennas. Its designed for use with either ladder line or coax. Use coax. On 75 meters you have about 80Khz where the swr is 2 to 1 or less. Your adjustment of the antenna determines where you want the 80 Khz range. I have all of 40 and 20 meters where the swr is 2 to 1 or less. You will probably need a tuner for 15 meters and some portions of 10 meters given the band's width. I would start without the tuner and see where you can go. Your specific location will determine how the antenna tunes. After a while you might add a tuner so you can extend coverage on existing bands and to get on 17 and 12 meters. Its a good antenna.
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