Question about dipoles ?

[Oatmeal]

I have worked the west coast using a Imax 2k which has been used for 10m only, still studying for my general, hoping to take my test in July, thats the earliest date I can take it here...

But thing is, I hear guys talking about using a dipole, and how I should do this and that, thing is I have about 72ft long span I have to hang a dipole in.....but to get any height or to reach the tree line, I'd have to cross the power lines, because if I was to go under them to get to the trees, a dipole would be about 20ft off the ground, then go up the hill to the tree line....this is a no, no if I was to do this ?...

The 72ft I mentioned, is what space I'd have from my drive way to the edge of the hill side, before you get to the power lines and the trees is above the PL's....I forget the lengths, but to work the 40-80m band I'd need a longer wire than 72ft span...I no I have to pass my general first, but just curious on this.....is there a right way doing this in my situation, if so what would you do ?...

 

[222DBFL]

Stay away from power lines with your antenna!!! Use another route. Bend the wire around. Find another way. But don't go over the power lines with your antenna or rope or anything for that matter IMO. What may seem harmless could result in some serious damage, and death. JMHO. The guys with wire antennas can help more on what to do, but I would look elsewhere to go. Again JMHO. I am faced with a similar dilemma here as I don't have the space for a proper long wire antenna. But power lines are an accident waiting to happen IMO. Good luck.

 

[vkrules]

STAY AWAY FROM POWER LINES...... Apart from the obvious safety issues .you want to minimize interference as much as possible .You could try making the dipole a inverted v or try a quad or delta loop. Loops take up less length and will also give you a lower noise floor. They will also work ok with the bottom wire only 2 or 3 meters off the ground.

 

[vkrules]

80 meter dipole is over 120 ft long.quad loop is about 65 per side.

 

[fourstringburn]

Yes, stay away from power lines!

I use a Carolina Windom as an inverted V which is a very good multi-band antenna for 10-80 meters.

This antenna for the 80 meter version is typically 133 ft but when used as an inverted V, the overall space is reduced by over 50 feet.

Since this is an off center fed dipole, one leg is 83ft. and the other is 50 ft. ( this varies between different commercially made versions of this antenna) .

At my location, I use a 45 ft. fiberglass push up pole that sits on the ground and attaches to the top of the A frame on the back my house and string the shorter 50ft. leg to my back wall and the longer 83 ft. leg goes over my house and hangs down from a tree branch with a weight on it in my front yard. The entire length is using about 77 ft.

With 2 different lengths of the dipole legs, maybe this this could work for you.

A inverted V maybe a good choice for limited space, either a OCF type like I use or other ones, However you must maintain and inside angle between 90 and 120 degrees at the antennas apex as shown below.

 

[mb91w126]

Yes, stay away from power lines!

I use a Carolina Windom as an inverted V which is a very good multi-band antenna for 10-80 meters.

This antenna for the 80 meter version is typically 133 ft but when used as an inverted V, the overall space is reduced by over 50 feet.

Since this is an off center fed dipole, one leg is 83ft. and the other is 50 ft. ( this varies between different commercially made versions of this antenna) .

At my location, I use a 45 ft. fiberglass push up pole that sits on the ground and attaches to the top of the A frame on the back my house and string the shorter 50ft. leg to my back wall and the longer 83 ft. leg goes over my house and hangs down from a tree branch with a weight on it in my front yard. The entire length is using about 77 ft.

With 2 different lengths of the dipole legs, maybe this this could work for you.

do the legs need to be @ 180* or can they be 90 to 120?? ish

I'm following this one closely as I expect to have my tech by next weekend and want to get on the long CW bands asap.

 

[fourstringburn]

On an inverted V, it's the inside angle as shown in the pic needs to be within that range of 90 to 120 degrees.

At 180 degrees, that would be a flat top straight dipole.

 

[vkrules]

do the legs need to be @ 180* or can they be 90 to 120?? ish

I'm following this one closely as I expect to have my tech by next weekend and want to get on the long CW bands asap.

No you can pull them in a bit to fit your block without any noticeable difference .

 

[Oatmeal]

How do you tune the swr on one of those dipoles without owning a 259B ant analizer ?

 

[Beetle]

How do you tune the swr on one of those dipoles without owning a 259B ant analizer ?

By determining whether the antenna, IN PLACE, is too long or too short by measuring reflected power (SWR) across the band (not just two or three places), and then shortening or lengthening as necessary to center the sweet spot at or near your favorite place.

 

[fourstringburn]

Typically, a simple dipole doesn't need tuning because there is nothing to tune. A simple mono band dipole is wire cut into two 1/4 wavelengths of the frequency used equaling a 1/2 wavelength of that frequency. About all you can do is trim the ends of each leg. This is where antenna analyzers come in handy. If you build your own dipole, then that's why it is suggested to use wire lengths that are a little long and then trim as needed. Most commercially made dipole antennas are pre-cut and should be close enough.

Multi-band antennas such as the Carolina Windom, G5RV, and others work by using a pre-determined lengths of wire and feedlines that will resonate on at least 1 fundamental frequency while being harmonically close to or resonant on other frequencies as well. This is why many of these antennas require using a antenna tuner. Usually the antenna tuner found in modern HF radios work fine, but if you decide to run an amp, then you need an external tuner capable of handling the amplifier load.

 

[DainBramage]

Typically, a simple dipole doesn't need tuning because there is nothing to tune.... About all you can do is trim the ends of each leg.....

actually a di-pole VSWR can be changed by changing the HAAT (height of the center support) or the height of the end supports or the angle of the wires @ the center conductor.

BTW, it is easier to just fold the ends of the wire back and then zip tie or tape or just bend the wire back until you find the lenght you want, its easier to just cut once than to solder back on a piece you just cut off

 

[The DB]

actually a di-pole VSWR can be changed by changing the HAAT (height of the center support) or the height of the end supports or the angle of the wires @ the center conductor

This is true, and the higher the antenna is in height and/or the more the antenna is folded over the lower the SWR.

One of those tends to be more difficult to play with, namely height. The cost of more antenna height quickly goes up, and goes up exponentially up as you raise a horizontal (or really any antenna) higher. Further, once you get past a certain point the gains you see start to level out.

Folding the antenna over more, while it will also lower SWR, has a cost as well, and the cost in efficiency is more than the very minor (and honestly, not noticeable at all) gain you will see from the lower SWR.

So to lower your SWR on a horizontal resonant antenna you basically have two options, more money spent or more losses. Either way you have a cost to consider...


The DB

 

[Captain Kilowatt]

actually a di-pole VSWR can be changed by changing the HAAT (height of the center support) or .......

Just to be picky for a minute but HAAT does not refer to the height of the antenna above ground. It stands for Height Above Average Terrain. Your antenna could be on a mountain top and only 20 above the ground however your HAAT could be several hundred or even several thousand feet. I just wanted to mention that for the benefit of those that may not be familiar with the term HATT or EHAAT which is Estimated HAAT.

 

[DainBramage]

Just to be picky for a minute but HAAT does not refer to the height of the antenna above ground.....

yeah, I realized that after I typed it soooooo, I just added in (height of the center support),.

I'm is a hospital on some serious meds, and,............. I just didn't feel like retyping it, doesn't make any sense NOW , but at the time of the post it seemed right