Discussion in 'Amateur Radio News' started by VK6FLAB, Oct 12, 2018.
Sounds like someone does not have a clue. !
About 25 years ago I wanted a 160 meter dipole. I used number 10 stranded wire and hung it all around the yard from 40 to 20 feet and fed it with twin RG8U coax directly into the rig. Much to my surprise it was 1:2 on 1.875 MHz.
Don't forget if you are going to communicate with the UK you must use their measurement "furlongs per forthnight" as your staring point. Then to arrive at the universal constant in antenna design you take the quantity of what you have, divided by what you want, the results being a constant multiplier for all other calculations.
In all the things that are said or written there is a truth, it is enough to look for it and not to be prevented.
I am looking forward to your correct dipole calculator, Onno. Allen VK6XL
And then multiply by the velocity factor. For 14 AWG stranded copper-ish stuff you get at Ham Depot, the VF is pretty close to 0.95, which will make 120.175 feet, or about 60 feet 1 inch per leg.
The 468/f formula already accounts for velocity factor, which is around .98 for insulated wire. The formula gets you "in the ballpark", there are FAR TOO MANY variables that are dependent on location, surrounding objects, height above ground, etc., to enable a precise calculation to be determined before the antenna is installed. Even then, changing environmental conditions, such as rain, snow, foilage on nearby trees, etc., will affect the antenna feedpoint impedance after it is installed. The only practical way to ALWAYS have a 1:1 match to an efficient antenna system is to use a tuner.
I stand corrected...you are right about the "468" already including the VF :
300 / 2 X 39.37 / 12 X 0.95 = 468 if the VF is about 0.95
Whenever I use the "468" rule, I nearly always end up further multiplying the result by 0.95 to get really "close" to 1.1:1 to 1.2:1 SWR. And that usually assumes a flat-top configuration, 20 feet in the air, no nearby obstructions, and Utah residential ground, and typical Utah humidity. There are other factors that affect the SWR, but these seem to be the biggest.