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Dipole question

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mvandyke37

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#1
Hi All
I have a line of trees above my house approx 30 yards linear up with an elevation change of approx 6-8 feet from the foundation of my house to the line of trees. The tallest tree is about 100 feet high in the air. My question is : Can I place the center dipole 50-90 feet up in that tree, and string the other sides along the tree line? Somewhere I read that this may cause problems. There are alot of trees, which is a buffer from my neighbors house whom lives on the other side of the trees above me, (Maryland terrain). The dipole would be in line with his garage, not his house. Do the lines need to be perfectly straight on the vertical plane coming out of the middle? I have researched extensively to find these simple answers, to no avail. In other words, can right side line be inverted down and bent at a 45 degree angle from the vertical plane? and the left side angled slightly of the vertical plane also?
I have searched long and hard to find this simple answer to these question with no results. I look at videos and i think I can do this, but would like expert advice.
ZS6BKW G5RV ZS80
 
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#2
There seems to be something inherently unclear in the way you're explaining this. You have a row of trees that are 30 yards from your house and about 6-8 feet above the foundation of your house? Think I got that part. What frequency are you working with? Are you trying to create some kind of modified inverted V antenna? As a general rule, stringing an antenna line across or close to anything that is conductive or semi-conductive will degrade performance. I think if you could give us a better visual it would really help.
 

mvandyke37

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#3
Hi Sir
My house is located right on the slant of a hill. The tree line I am talking about is located at the highest point of the terrain, which is fortunately right above my house at an elevation of 6-8 feet above my house and approx. 20-30 yards linear from the cable entrance to my house. My idea is to string the dipole center up in the highest part of the 100 foot tree as possible. The 100 foot tree hangover is located very close to the center line of my house. If I fan the right and left sides of the dipole, they will be next to the line of forest. So, I plan an inverted V approx. 30 degrees down.
The question is can I angle the right or left side away from the line of forest?
My primary bands would be 80 to 12, with an emphasis on 40, 20.

Thanks
 
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#4
I believe what you are describing is an inverted "V". Yes this can be done. Best results are obtained if the included angles are greater than 90 degrees. Most dipoles have both legs in a straight line. The ends can droop but the best results will occur if the included angle is between 90 and 180 degrees. The inverted "V" then brings the ends closer together and again best results will occur if the included angele is greater than 90 degrees. Also the higher you can get the ends above the ground the better. This type of antenna a little more directional. Fed with ladderline and a balanced line tuner this antenna can be an excellent multi-band antenna.
BB
BB
 
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#5
Honestly, you can do whatever you want! Rules: keep the ends as far away from each other as possible (for a dipole, not talking about Vee Beams or such), put it up as high as possible (100 feet is excellent), and keep the ends in the clear (so the wire isn't laying in wet branches). Put it up, and try it. Once you see it up there, then you'll think of ways to change it / improve it. Sounds cool!
 
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#7
Going back to the original question, it's certainly possible to put up an antenna as was described. It will have some slight losses because it's close to things, but those losses are not going to be huge, that's about as typical as it gets.
I'd also suggest not going too far with that inverted dipole thingy, the angle between the legs certainly do not have to be as small as described (45 x 2 = 90 degrees). One of the things those 'drooping' legs do is lower the input impedance. If it started at 70 - 75 ohms, letting the legs droop to something like 120 degrees will get that input impedance down closer to 50 ohms, and that's good (also a very common way of getting a good match).
I wish I had a tree that was 100 feet tall! It'd be nicer than what I commonly make-do with. An antenna doesn't have to be 'ideal' by any means to do just fine.
- 'Doc
 

wbswetnam

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#8
Yes, "the higher the better" is the general rule for a dipole. But keep in mind that in no way does it have to be perfect to make lots of contacts. I think that I have just about the worst antenna possible: a fan dipole mounted in the attic of a single-story home, with my power at 100W barefoot. Bleeech! But I am making contacts on both coasts (I am located in Arkansas) and many international contacts in Europe and Central / South America. I had a QSO just yesterday with Venezuela, and the day before that, France. Both gave me a 5-5 signal report. So, don't worry about perfection. Get that wire up in the air and grab that mic. Have fun!
 
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#9
Height depends on the band and who you want to talk to. For the best regional contacts (out to 500mi or so) on 40/60/80m the best height is around 1/4 wavelength at the highest NVIS band, or about 33ft. This is assuming a flat top dipole or the apex of an inverted V would be similar.

For best DX its good to have the dipole multiples of 1/2 wavelength above the ground and about 65ft would be good for 40, 20 and 10m leaving 80m at the best height for NVIS or regional coverage. A low dipole doesn't mean regional NVIS either, an antenna 10ft off the ground will certainly talk coast to coast on 80 or 40m but just not very well compared to one higher or at 1/2 wavelength up.

My main HF antenna is a flat top dipole about 30ft high and I'm very pleased with its NVIS and DX performance.
prcguy


Yes, "the higher the better" is the general rule for a dipole. But keep in mind that in no way does it have to be perfect to make lots of contacts. I think that I have just about the worst antenna possible: a fan dipole mounted in the attic of a single-story home, with my power at 100W barefoot. Bleeech! But I am making contacts on both coasts (I am located in Arkansas) and many international contacts in Europe and Central / South America. I had a QSO just yesterday with Venezuela, and the day before that, France. Both gave me a 5-5 signal report. So, don't worry about perfection. Get that wire up in the air and grab that mic. Have fun!
 
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#10
What is this preoccupation with 'NVIS' antennas, and assigning particular ranges/abilities to them? In most cases that NVIS distinction is nonsense/worthless. Antenna height alone isn't going to assure anyone of any particular ability or range limit.
- 'Doc
 
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#11
Not a preoccupation, just stating facts. Put a 40m dipole up at say 1 wavelength and try to make a contact to a station with the same setup at 200 or 300mi. If it works at all the signal level will be grim at best, even with the best conditions. Lower the antenna on one of the stations to 30ft and now it works somewhat. Lower them both to 30ft and it now works great.

Same holds true with two vertical antennas with good ground plane under them, there will be a difficult to reach area beyond ground wave, which fades out around 75-100mi and the first skip zone. A horizontal antenna at 10ft or 30ft will saturate the 0 to several hundred mile range bouncing between 40 and 80m depending on time of day,

I've proven this with my own antennas over and over again for almost 40yrs and had verticals that could not make contacts with another vertical 150mi away on 40 or 80m where a horizontal dipole at the same site worked just fine. I currently have a remote radio in MA with selectable 43ft vertical with massive ground system and a 94ft dipole at 30ft (ZS6BKW) and do real time testing all the time to my home station located in So, CA. The 43ft vertical in MA always works better on 40 and 60m DX to CA and sometimes 80m, but the 43ft is not optimized for 80. For New England and stations within about 500mi of my MA station, the horizontal dipole always works better on 40, 60 and 80m, the bands that favor NVIS propagation.

The NVIS concept is well researched, well known, very predictable and very real in my experience. Kind of like the sun rising in the east every morning and not some other direction. Look at any ARRL antenna publication dealing with HF antennas or most any modern military antenna handbook for setting up antennas for specific purposes, they all spell out the details for NVIS or long haul based on antenna type, height and other factors.
prcguy


What is this preoccupation with 'NVIS' antennas, and assigning particular ranges/abilities to them? In most cases that NVIS distinction is nonsense/worthless. Antenna height alone isn't going to assure anyone of any particular ability or range limit.
- 'Doc
 
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#12
"Put a 40m dipole up at say 1 wavelength and try to make a contact to a station with the same setup at 200 or 300mi."
Easy, bnut I get to pick the time of day.

"Same holds true with two vertical antennas with good ground plane under them, there will be a difficult to reach area beyond ground wave, which fades out around 75-100mi and the first skip zone."
What bad is this 'ground wave' on? Once above the lower HF bands there is no 'ground wave' as it's commonly though of.

I can count the number of times I've had an antenna above something like 1/4 wave above ground on one hand. Hasn't stopped me from doing a lot of 'distant' things. May have to wait till 'Moma Nature' decides to change her propagation, but everyone has to do that. It's also a simple fact that 'height makes might' in the majority of circumstances. Gotta be careful with those 'facts'!
'NVIS' is an unecessary and limiting name that doesn't always apply for almost any circumstance.
- 'Doc
 

bill4long

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#13
What is this preoccupation with 'NVIS' antennas, and assigning particular ranges/abilities to them? In most cases that NVIS distinction is nonsense/worthless. Antenna height alone isn't going to assure anyone of any particular ability or range limit. - 'Doc
I don't know what you've been smoking, but NVIS is well known, well understood, well documented, and has been well-used by the United States military for a half dozen decades. Quite simply, you don't know what you're talking about.
 

wbswetnam

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#14
Well, certainly there are a lot of opinions and theories regarding antenna height and configuration. The antenna you choose to put up can certainly affect your ability to work DX but even with less than desirable antennas like mine, good contacts are very possible. This afternoon, for example, 15m was BOOMING in from Europe. In 15 minutes I worked Hungary, Greece and Italy with ease... almost no QRN or QSB at all. I'd have stayed with it and made more contacts, but the World Cup called and I had to go watch!
 
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#15
"I don't know what you've been smoking, but NVIS is well known, well understood, well documented, and has been well-used by the United States military for a half dozen decades. Quite simply, you don't know what you're talking about."
Smoking? Only over the counter stuff, and I'm not in Colorado. "...half a dozen decades."? Imagine that, 72 years, something like the 1940's? I would suggest you do some studying about military communications. You may be surprized at their philosophy. And just for grins, I did patches during 'Shield' and 'Storm'. Antenna was maybe 20 feet off the ground at it's highest point. But what do I know, right?
- 'Doc
 
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#16
A low horizontal dipole works fine for DX and I use one every day for that. However it will work MUCH better for DX at a half or full wave up but the 80-60-40m coverage from around 75mi to several hundred miles will suffer greatly if the other station has the same setup or they have a vertical antenna.

A vertical with a lousy or insufficient ground below it like a trap vertical on a short pipe in the ground with no radials can have some upward radiation and contribute a little to NVIS propagation where the same antenna with a substantial ground will pull the pattern down towards the horizon and have a null overhead and you loose maybe 10 to 20dB NVIS contribution. Both stations using vertical antennas with low takeoff angles, a big null overhead and trying to talk 150mi will probably not work on any band at any time.

Ground wave is a common term for propagation over land, without a high angle (NVIS) bounce off the ionosphere (you know this) and it has a finite distance, not counting a low angle bounce off the ionosphere and landing hundreds or thousands of miles away. This has all been documented and figured out before we were both born.

I would say maximum useable range on the lower HF bands with typical trap or other moderate size verticals at both ends of the circuit is usually less than 100mi, then you have a dead zone until the first low angle bounce off the ionosphere, which will be quite a distance, leaving a dead zone from 75mi to hundreds of miles out. If one station is using a low dipole then it usually fills in enough to make a contact to the vertical on the other end.

Then you have military communications like recent events in the middle east where HUMVEE's get out of VHF lo-band range around 30mi and use HF out to a couple of hundred miles. They have to bend their 16 or 32ft whips over horizontal to improve HF comms in that range where the perfectly vertical whips do not work very well. In many cases the military base HF antenna is a 32ft vertical whip with a few ground radials and a coupler at the base, not good for the typical HF distances they were using when both antennas are vertical.

Again, I'm not making this up, its all in textbooks but I am a heavy user of HF and probably spend about 360 days a year on HF or with a radio playing in the background and its also my experience. Maybe the OP should look up some antenna propagation books from ARRL or the excellent US Army publication "Antennas and Radio Propagation" TM 11-666, and not listen to our bickering.

BTW if he does get some books I think he will find my comments are more on track :)
prcguy





"Put a 40m dipole up at say 1 wavelength and try to make a contact to a station with the same setup at 200 or 300mi."
Easy, bnut I get to pick the time of day.

"Same holds true with two vertical antennas with good ground plane under them, there will be a difficult to reach area beyond ground wave, which fades out around 75-100mi and the first skip zone."
What bad is this 'ground wave' on? Once above the lower HF bands there is no 'ground wave' as it's commonly though of.

I can count the number of times I've had an antenna above something like 1/4 wave above ground on one hand. Hasn't stopped me from doing a lot of 'distant' things. May have to wait till 'Moma Nature' decides to change her propagation, but everyone has to do that. It's also a simple fact that 'height makes might' in the majority of circumstances. Gotta be careful with those 'facts'!
'NVIS' is an unecessary and limiting name that doesn't always apply for almost any circumstance.
- 'Doc
 

Cunnerman

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#18
I just want to jump in here and say that this thread is very interesting for two reasons. The first, of course, is the antenna material being discussed,

The second is the fact that even with a disagreement between two very sharp operators, both parties have remained civil and cited their examples and generally advanced the discussion. It seems that rarely happens on another popular radio website.
 

hd625b

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#19
Safety

How would one go about grounding an antenna installation discussed above? Trees make good targets for lightning strikes and 100 foot tall trees make even better targets.
 
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#20
A dipole antenna doesn't need "grounding" in the general sense. A dipole by its nature doesn't need a ground. The ground however may alter some of the radiating and impedance characteristics of a dipole. As for grounding a dipole one should at a minimum have a surge arrestor on the feed line (coax or balanced line). If fed with coax the NEC requires the braid of the coax be grounded before it enters the building. This ground could consist of a combined ground and a surge arrestor such as a polyphaser. The arrestor would be connected to a ground rod placed near the entrance to the building. The NEC also requires that all ground rods be connected to the main building electrical ground.
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