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1-8 of 8 messages
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HF Longwire antenna for a farm
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by NOVICE351 on April 25, 2006
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G'day guys from Australia
I have recently become licensed (finally) and wish to set up a 1 and one half wave dipole on 80 meters (yes I know it will be very long), on our farm in Southern NSW.
I mainly want to catch up with some old friends in the States on 80 and 40 meters.
I was thinking of feeding it with an MFJ tuner and running coax into a Balun at the feedpoint.
Any ideas, will it work and if so has anyone had any experience?
73's from Downunder
Max
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RE: HF Longwire antenna for a farm
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by K0ZN on April 25, 2006
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G'Day, Mate!
Short version: If the antenna is 3 HALF waves on 80 M
(approx. 390 ft.) it can be fed in the center with coax and a balun and have a good match/low SWR because the feed point impedance is low, near the impedance of the coax. However on 40 M you will have a "Zillion to 1" SWR because you will have an EVEN number of half waves (approx 6 ), which yields a HIGH impedance feedpoint...like possibly 2,000+ Ohms...yielding about 40:1 SWR! If you want to use that antenna on 80 and 40 you are going to need to feed it with 450 ohm ladderline, 600 ohm open wire line or some other high impedance balanced line (and a Tuner with a balanced output) because the losses in that type of line are low even at high SWR. Losses in coax even on the low bands get substantial at very high SWR...you will also have some very high VOLTAGES at a high SWR...maybe exceeding the ratings on the coax at high power levels.
Suggestion: That type of horizontal antenna is NOT a particualy good antenna for DX long haul contacts...it would be good for work around VK land, but the radiation angle is high making it a poor choice for DX. If you have a large amount of room, put up some kind of vertical antenna or vertical radiator...these antennas have a LOW angle of radiation and are MUCH better for DX. Pick up a copy of ON4UN's excellent book "Low Band DXing"...it is really a supurb antenna book...well worth the money.
Good luck on your project. 73, K0ZN
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RE: HF Longwire antenna for a farm
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by KG4SGP on April 25, 2006
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I don’t know about the impedances as well as K0ZN but you might want to think about Beverage antennas. Just if you’re wondering it’s basically a long wire (100m and longer) running in (primarily) one direction and terminated at the end with a resistor. They've got patterns that look like yagis but they work on 160m and 80m.
Good luck and hope to hear you on the air.
73s KG4SGP - Jim.
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RE: HF Longwire antenna for a farm
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by WB2WIK on April 26, 2006
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>RE: HF Longwire antenna for a farm Reply
by KG4SGP on April 25, 2006 Mail this to a friend!
I don’t know about the impedances as well as K0ZN but you might want to think about Beverage antennas. Just if you’re wondering it’s basically a long wire (100m and longer) running in (primarily) one direction and terminated at the end with a resistor. They've got patterns that look like yagis but they work on 160m and 80m.<
::Beverages are for "receiving." You wouldn't use one for transmitting, they're inefficient.
::I agree if you want to work Stateside from VK on 80 and 40 (especially challenging on 80), you probably want to use a vertical, a vertical loop, a vertical array, or something to get your signal down closer to the horizon than a horizontal 3/2-wave dipole probably can -- unless you have some way to get that dipole very high above ground. Either that, or work only very "big gun" Stateside stations who have truly great antennas, in which case they can work anybody anywhere, so you don't have to do that much. But there aren't that many of "them..."
WB2WIK/6
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RE: HF Longwire antenna for a farm
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by WW5AA on April 26, 2006
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Hey ya all, (AR hillbillie talk)
I work VK and ZL a lot with my 5BTV, roof mounted and 4 radials per band for transmit and a choice of coaxiale ½ square or 512' beverage for receive on 80 and 40 meters. It is easier on 40 meters to use the beam but always love the challenge of doing it on inexpensive antennas. Last contact was VK3IO in the 80 meter DX window. It helps to have 1500 watts available…LOL. Good luck and catch you on the low bands.
73, de Lindy
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RE: HF Longwire antenna for a farm
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by WB6BYU on April 26, 2006
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If you can get your antenna up 50 metres in some gum trees
it may work fairly well. You will need to aim it, though,
as the pattern will be somewhat directional. But if it is
only 10 metres high then some sort of vertically polarised
antenna will be far better for DX. (The dipole will be
better for VK1/VK2/VK3/VK7, though.)
Here is some good reading on simple wire antennas that
should work at comparatively low heights:
http://www.cebik.com/scv/scv0.html
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RE: HF Longwire antenna for a farm
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by AA4PB on April 26, 2006
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The beverage is an inefficient antenna therefore it picks up less noise and makes a good low band receiving antenna. You certainly would not want to use one for transmit. Most of your power will be going to heat up the resistor.
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RE: HF Longwire antenna for a farm
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by KG4SGP on April 26, 2006
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Sorry for got and as you can, most likely, tell I dont play much around 80 or 160. I would like to however. I might put up a long wire and tune it up. Dont have the room or desire to put up a tower yet although.
73s KG4SGP - Jim
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