ANT. help

[biferi]

If I want to make a Dypole ANT. it will have a Line coming from the Left and Right side of it.

Now I need help with how to findout how long I make both ANT. Lines.
I know you take the FREQ. you would like to get in MHz and then Divid it by something.

Or do something with the Center FREQ. then Divid by something and that is how long the Left and Right Line will be.

Please help

 

[BJ radionut]

1/2 wave dipole antenna

468/freq in Mhz= 1/2 wave/2=1/4 wave(each side)

EX: 468/28.5 Mhz=16.42ft(16ft 5in.)/2=8ft 2 1/2in(each side...
solder one length to the shield/one length to center conductor...

Amateur Radio Antenna Projects

Have fun
All the best
BJ

 

[W5LZ]

And just a little hint to make things a bit easier.
The numbers you come up with using this/these formulas are slightly 'too long' measurements. Not much 'too long' but some. That gives you a sort of 'safety margin'/'fudge factor' when tuning the thing for resonance. Too long is a lot easier to deal with than 'too short'. It's also a sort of good idea to add just a little bit more to that measurement so that you have enough wire to make connections, wrap around insulators, etc. The only 'trick' to the whole thing is to keep the 'sides' of a dipole/doublet of equal length (at least close!). You will have to do a bit of 'trimming' to get the final 'right' length, but you'll have to do that anyway, no biggy.
The type/kind of wire you use for antennas isn't critical at all, it just has to be able to conduct electricity. It also has to be strong enough to hold up it's own weight and a little bit more. Stretching is not exactly good, so a 'harder' type wire is nice. Stranded or solid makes no practical difference, neither does insulated/uninsulated. Whatever you happen to have the most of will probably work just fine. Anything larger than about a 10 ga. is really over kill unless it's a very, very long antenna, #14 works very well, easy to handle, cheaper too! Got miles of #8 wire? Use it, it'll just weigh more. (Can I have some??)
After you've been around this stuff for a while it'll all seem like common sense. Common sense takes a while to learn though. Have fun!
- 'Doc

 

[biferi]

tneed some more help

468 Divided by FREQ. in MHz = Length of wire in FEET then take that and cut it in halfe and that will make the two ends left and right???

And what is the 468 stand for??
Thanks for all the help

 

[Beetle]

468 Divided by FREQ. in MHz = Length of wire in FEET then take that and cut it in halfe and that will make the two ends left and right???

And what is the 468 stand for??
Thanks for all the help

468 = an empirical constant that will get your antenna close but probably a little bit too long. You then adjust it carefully for the exact frequency you want to set it for. No two installations are the same; 468 will be close enough to start.

 

[biferi]

freq help

So do I have it now 468 Divided by FREQ. in MHZ gives the length of wire in FEET then I just cut that in half and that will give me the left and right sides of my ANT???

 

[BJ radionut]

 

[W5LZ]

biferi,
That's about it. Not all that difficult really. That number, 468, is the 'practical' value for finding the length of a 1/2 wave length of some frequency for wire antennas. To understand how that 'practical' number is arrived at requires some study, isn't really something to get here or any forum. It can get fairly complicated depending on how much math you happen to have, but really does make sense when you finally get your mind 'around' it. Some people find it really interesting, some don't. How 'deep' you want to get into it is up to you, so suit yourself. The main 'thang' is to have fun at it.
- 'Doc

 

[biferi]

I think I am getting a little mixed up here??

You did tell me 468 divided by FREQ in MHZ = Length of wire in FEET and then I just cut that in two to get the left and right lengths of wire for my ANT.?????

And is 18 Gauge wire ok??

Soory just tell me these 2. things

 

[W5LZ]

That, 468/f(Mhz)= feet, is the total length of the antenna. Half of that figure will give the length of each 'side' of the antenna. The center point being where the feed line is connected to each 'side'.
Number 18 wire will work fine for 'shorter' antennas. That 'shorter' is variable, sort of, but basically means that 18 gauge wire may not be strong enough to hold it's own weight, plus the feed line's weight, in longer spans. Strength and weigh determine how large the wire should be.
Probably the most common size of wire used is a 14 guage. Primarily because it is of fairly common usage for other things, electrical wiring, etc. It's typically strong enough for spans ranging up to about 200 feet or so. Probably strong enough for longer spans but those longer spans are not really very common for antennas, sort of. There's no 'magic' concerning this size of wire, just kind of 'typical'. A number 18 wire ought to work okay.
- 'Doc

 

[TonyV225]

There are some really cool books on this you could look into buying or getting from your local liabrary There really interesting and as said its not hard you just follow directions as there writen. I have a cool book Ill dig it out and tell you what its called. It has formulas for every band and whats needed which is most all of it can be purchased at Radio Shack.