Everything you know about dipole (calculators) is wrong ...

I find it interesting that an article for beginners that criticizes the accuracy of these dipole calculators would use the number 486 in the post. Beginners need accurate information not mistakes in a post - it just adds confusion.

 

Nice shot. Cheap, but nice.

Then the smart phone generation isn't so smart after all.

 

Onno. Thanks for posting your findings. And I'm glad you continue to do so even when these old farts get mad over silly things like people using a dipole calculator. Oh my God, how dare they. They all use computers or they wouldn't be here knocking down everyone for posting some info or findings. And so a question for the old timers... why do you use email, when you could send a letter? Why send a letter if you could drive to a business and do it face to face? Even better yet, why drive at all when you could walk? Ahhh yes... technology. It's all around us to make life easier, and who are you to blame another for using it?

 

I'm sure you hammered this post out on your typewriter, passed it along the pony express to a modern HAM with an electronic device for them to post here correct?
Just kidding.

 

I use both email and the postal service. When immediacy matters, I choose email - when timeliness is of less importance, I use the postal service.

If it's a priority matter and cost effective, I do drive to a business and conduct whatever face to face.

I frequently walk to the post office and various businesses.

I'm not a Luddite, but I do find the following to be both tragic and hilarious:

 

Anyone that can’t calculate a 1/2 wave antenna on a scrap of paper and then constuct it isn’t worthy of being called an amateur radio operator. It just doesn’t get any more fundamental than this.

 

Velocity factor? Certainly matters if you are building a phasing line.....

 

Whenever I have the need to make sure an antenna is correct I use the RigExpert AA-600 I have. The theoretical dipole size is just a starting point.

A well tuned antenna is the best you can have - tuners is in reality not a substitute for a good well-tuned antenna.

 

While we're kicking around dipoles, here's a good read: https://www.eham.net/articles/23802

I fall into the let's see what my AA-230 says about my piece of wire and I'll go from there group.

 

You're*
73 de 9A5AEU

 

Whenever I come across an article that has in the title "you're doing xxx wrong" I read. It's the non-picture equivalent of a "...and then THIS happened" click trap, I know ... but I am compelled to do so. The calculation for the length of a dipole hasn't changed, and 468/F(Mhz) is still the formula. As for "ground", you're kinda stuck with what you have. Install the antenna a half-wave or higher above ground if you want DX .... install it ~.2 wavelengths above ground if you want "NVIS" operation. Even if you calculate to the millimeter, when you're done with your "calculator", you're still gonna add some length to your answer so you can trim until you get the match you want with your transceiver. Making simple things complicated is the job of academia ... it's not supposed to be what we do. That's why we're called "amateurs".

 

Okay, there are shortcut, ballpark formulas that any ham should be able to use with some degree of accuracy. Then there is the actual formulas based on physics that we should know, even if we don't use them. Which ever you use, be sure to cut the sides of the dipole extra long and fold them over at the ends so you can use the extra length for fine tuning in the field, if necessary.

If you want the physics formula, then here it is. BTW, scientific and engineering formulas are calculated in metric, not American Standard, unless you want to crash your billion dollar space craft into the surface of Mars...

Calculate a one wavelength antenna with this formula: Wavelength = Speed of Light in meters/sec * Velocity Factor / Frequency in Hz

Speed of Light in vacuum of space = 299,792,458 meters/sec

Velocity Factor: Unless you are building an antenna in the vacuum of space, you will need to adjust for the rate of speed in which an electromagnetic field can travel through a medium, like a dipole copper wire. Yes the speed of light is 299,792,458 meters/sec in the vacuum of space, but it is going to travel through a 14 gauge stranded copper wire on Earth at a different rate than it would travel in the vacuum of space. Therefore you need to know the velocity factor ratio (VF) for the medium you are using. For example, for #12 or #14 insulated wire the VF = around 0.94, but for RG-58U coax the VF = around 0.66. So look it up for the medium you will use.

Tuned Frequency of Antenna: If you are going to build an antenna you obviously need to know which frequency you want to have it tuned for. For example, let us say you want to have your antenna tuned for 7.200 MHz in the 40m band. For the formula, use hertz rather than megaherts, so 7.200 MHz = 7,200,000 Hz.

Example: Let us calculate a full wavelength for a wire antenna using #14 stranded copper wire tuned to 7.200 MHz (40m band).

Wavelength = Speed of Light in meters/sec * Velocity Factor / Frequency in Hz

Wavelength = 299,792,458 meters/sec * 0.94 / 7,200,000 Hz = 39.13957091 meters

Remember that this is for a full wavelength. If we are going to build a 1/2 wavelength standard dipole, then we need each side of the dipole to be 1/4 wavelength, so the length of each 1/4 wavelength side needs to be 39.13957091 meters / 4 = 9.784892726 meters. That converts to 32' 1.23". (One meter = 39.370079 inches or 3.28084 feet.) This of course assumes the 1/2 wavelength standard dipole will be erected horizontally at 1/2 wavelength above the ground. There are also other factors such as ground/earth type below the antenna and height of antenna, and angle of antenna in reference to the ground/earth, etc. You can make it as complicated as you want, or as simple as you want. Bottom line though is always make it longer than your calculations so you can adjust it if necessary.

 

I seen the intended humor in the article.

Thanks.

 

Whew!

My turn:

234 / 7.2 = 32' 6"

Moral?

KISS, silly.

 

If you want real confusion, try looking for calculations for an EDZ. Every source I've seen uses a different "magic number". I simply found a bunch of those "magic numbers and averaged them out to come up with 1234. Easy to remember. I've enjoyed reading the article and especially the replies.

73, Kirk K9WW