Best Dipole Setup

[Riverman]

http://hamuniverse.com/wb4yjtdipolepatterns.html

According to the above article, The Best Dipole Setup is somewhere between 20% and 15% wavelength height, where a dipole's impedance crosses 50 Ohms.

For an 11 meter dipole designed for 27.2 mHz with a wavelength of 34.2 feet, this would be a mounting height of around 6 feet, which is pretty darn low.

From the article:

This is not the ideal DX antenna, but it does provide good signal strength at reasonably low angles (6 dB down at 20 degrees elevation angle). It is essentially the same pattern as the .25 wavelength height dipole, but with the benefit of being matched to 50 Ohms. In addition, it provides a very broad NVIS signal lobe. This looks like a good compromise between both modes, and is fairly easy to set up on frequencies above 10 MHz.

Thoughts?

 

[binrat]

Hmm, how did you know that I'm building another dipole tonight...

I've been doing strictly SOTA this summer, 20 metres ssb. Inverted V dipole using an avi probe with a height of 8'6". Yesterday I compared it to the height of approximately 15ish ft during the activation and saw the swr drop down to a point where my KX2 shown a very low swr and no need to tune.

 

[Riverman]

Hmm, how did you know that I'm building another dipole tonight...

I've been doing strictly SOTA this summer, 20 metres ssb. Inverted V dipole using an avi probe with a height of 8'6". Yesterday I compared it to the height of approximately 15ish ft during the activation and saw the swr drop down to a point where my KX2 shown a very low swr and no need to tune.

I once had a small dipole made from 2 Firestik mobile antennas and the SWR was lower on one 5' section of mast than on three (15'). One never knows.

 

[codeman]

I use two 4' foot antennas with a bracket for horizontal mounting, I have it mounted on a painters pole. My swrs are about 1.4 on 19 and about 1.9 on channels 1 and 40. I have it about 10 ft high.

 

[Riverman]

I use two 4' foot antennas with a bracket for horizontal mounting, I have it mounted on a painters pole. My swrs are about 1.4 on 19 and about 1.9 on channels 1 and 40. I have it about 10 ft high.

Might need to drop it down to 6' LOL. Mine was made using 4' Firestiks with the tunable tips. With a few twists on each I was able to get almost flat SWR's.

 

[Riverman]

Hmm, how did you know that I'm building another dipole tonight...

I've been doing strictly SOTA this summer, 20 metres ssb. Inverted V dipole using an avi probe with a height of 8'6". Yesterday I compared it to the height of approximately 15ish ft during the activation and saw the swr drop down to a point where my KX2 shown a very low swr and no need to tune.

Binrat,
I might have misread your post. Was SWR lower at 8'6" or 15'?

 

[binrat]

It was lower at the higher height. I put it as being an inverted I never raised the ends thus bringing it into a better match. It was always off and too easy to push the tune button. I also saw an increase in the noise, from S1 to S3.

 

[Riverman]

It was lower at the higher height. I put it as being an inverted I never raised the ends thus bringing it into a better match. It was always off and too easy to push the tune button. I also saw an increase in the noise, from S1 to S3.

Okay. I misunderstood. Thanks.

 

[Riverman]

Hmm, how did you know that I'm building another dipole tonight...

I've been doing strictly SOTA this summer, 20 metres ssb. Inverted V dipole using an avi probe with a height of 8'6". Yesterday I compared it to the height of approximately 15ish ft during the activation and saw the swr drop down to a point where my KX2 shown a very low swr and no need to tune.

Ever considered an Alexloop for SOTA?

 

[binrat]

Ever considered an Alexloop for SOTA?

Not really. With the avi probe as a mast my setup is about 3 lbs, With my fiberglass mast its almost 5 lbs. I have a full spool of Army fieldphone wire so dipoles for years.

 

[Riverman]

Not really. With the avi probe as a mast my setup is about 3 lbs, With my fiberglass mast its almost 5 lbs. I have a full spool of Army fieldphone wire so dipoles for years.

Very good. Have fun!

 

[vkrules]

You dont want a NVIS signal lobe on 11m .Dipole is going to work a lot better at 15 ft than 6 . Impedance be buggered !!! The difference between 50 and 70 ohms is negligible. Anyway horizontal dipole has to be high and in the clear to see 70 -72 ohm At 1/2 wave I typically see 65 - 68 at resonance SWR 1.3 And a Inverted v is closer to 50 ohms. because of the angle of the legs and is vertical polarized

 

[codeman]

Might need to drop it down to 6' LOL. Mine was made using 4' Firestiks with the tunable tips. With a few twists on each I was able to get almost flat SWR's.

I use two cheap fiberglass antennas, I think they are Mobile Tronics brands or something like that. I 've used one on my pickup and it did a great job. It really pulled in the weather channels. I am able to get weather bands from 70-90 miles away with it. Anyway they have rings that loosen then you just unscrew or screw in the tip to set the swrs. Makes it easy. I may try it at 6ft. just to see what happens. I also run a dr.dipole antenna in an inverted v at about 10-11 ft. at the feedpoint. When skip is rolling i can make some decent contacts. The inverted v works much better for local talk as it should.
I live in a townhouse with a small patio, so I have been trying to have my fun with the radio while not stirring up the neighbors. Trying to keep it as stealth as possible.
I have been thinking about putting the dipole up to 18ft. to see how that would work. I am gone 4-5 days on the road so I don't have much time I would like at home to mess with the radio and antennas.

 

[Paul-W5lz]

Whats the 'best' height for an antenna (dipole, whatever)? As high as you can get it. What does that do? It means it can 'see' further without having to 'bend' (propagation).
All antennas have two characteristics you have to deal with. One is how efficient it is, how well it radiates. The other is matching it's input impedance to the rest of the antenna system (feed line, etc.). Resonance is very nice! It means that the antenna is as efficient as it can get (probably), that's the biggy. Whatever amount of power get to the antenna gets radiated, instead of lost in some way. The most common way of doing that 'resonant' thingy is by adjusting length, or tuning the antenna. (If you don't have to do that tuning then you got a miracle, enjoy it.)
The other part, matching impedances, is something that almost always has to be done, it's not unusual at all. This part is probably the most difficult because it requires some knowledge of what impedance is. It ain't simple! But that SWR meter is very 'simple', just can't understand about what impedance is made of, can be as wrong as much (if not more) that it's ever right. A tuner is a very nice thingy to have, believe it or not. Or a better name for it is an 'variable impedance transformer'. It does the same thing a voltage transformer does to 120v to change it to 12v, except with impedance rather than voltage. Any losses? Sure, but not nearly as bad as the impedance mismatch you started with.
None of this is 'new', you've probably seen it a thousand times...

 

[Riverman]

I have always had difficulty wrapping my mind around the notion that small differences in impedance are unimportant, and the difference between 70 ohms and 50 ohms is negligible.

Until now.

According to the author's chart in my Post #1, the lowest SWR he was able to obtain at 70 ohms was about 1.4 and the lowest at 50 ohms was about 1.2.

According to every chart I've ever seen, an SWR of 1.2 typically results in a power loss of .8%, leaving 99.2% power available at the antenna. For an SWR of 1.4, it is 2.8% and 97.2% respectively.

For a radio transmitting 4 watts, this difference is only .08 watts which is indeed negligible.