VK6ZGO wrote:I don't think "F"calls should get used to magic formulas like 468/f in MHz which give the length in feet.
We are a metric country,so it is more instructive to use 300/f in MHz, halve it,multiply it by 0.95 for "end effect",& you have it.
After all,it's a halfwave dipole on "10metres",so there is a fair chance it will be around 5metres long.
I agree that we should be using 300/f MHz as that is exactly what is in the foundation manual however there's probably plenty of F calls that are quite comfortable with imperial measurements especially if they were born in the 60's or earlier.
There are many designs on the internet and in books that use 468/f but it's easy to convert.
Google tells us that 1 foot = 304.8mm or rounded up = 305mm
So, using the measurements in the video we apply the following
305 x 8.25 =
2516mm rounded down
compared to the nicer alternative of 300/f in MHz
((300/28.3) x 0.95)/4 =
2518mm rounded up
We shouldn't be surprised that the mathematics works.
An F call and I went out with little preparation to participate in a HF contest. We took an untested dipole with us that was "guaranteed" to work on 80m. I also took a 100m roll of building wire with me "just in case".
Well, the gifted dipole didn't present a good VSWR on 80m and in fact looked like it was cut for 4.5MHz. Anyway, with 90 minutes to go we had to get something working on 80m. Applying the method outlined above we had a 80m dipole strung up in 20 minutes that worked a treat.
The F call was amazed that it was so simple to get an antenna going on HF.
So great work Randy. I know there are many hams out there of all classes that don't know or don't trust themselves enough to do something like this. I smile when I see folks singing the praised of their new $300 wire antenna - it ain't that hard to do something with wire for much cheaper.
P.S. I found out later that the other dipole was supposed to be some kind of G5RV. Note to self, don't take untested gear into the field.
