dipole questions

[blueangel-eric]

When building dipoles i always get confused at the length. if it calls for 18 inch elements is that 18 inches altogether or 18 inches from where you tap the feedline/wires to the end?

What is better a direct connection such as a beta match or a gamma match? I know beams mostly use a gamma match so would a standalone dipole also be better for one? though those are more time consuming to construct.

Eric Burris

 

[ke5ldo]

Use this formula 468 divided by frequency in MHZ=total length divide by 2 for each leg
234 divided by Frequency in MHZ = the length of one leg.
This should help.

 

[blueangel-eric]

Use this formula 468 divided by frequency in MHZ=total length divide by 2 for each leg
234 divided by Frequency in MHZ = the length of one leg.
This should help.

that's not quite what i was asking. does a dipole lenght count from where its attached to a rod or boom or does the measurement stop where the feedpoint is tapped? so if i want a 18 inch element on each side do i cut it for 19-20 inches so when i tap it i would be right? sometimes the feed point is adjusted up or down for SWR's so then the lenght is actually shorter. reason i'm asking is when i make a dipole the first inch or two goes into the pvc T Connenctor and i tap it further up the element. so do i measure the lenght from where i tap it or from the end of the rod in the PVC? it gets confusing when i try to build beams with that measurement hurdle.

 

[N1BHH]

468 divided by the frequency is the total length for a half wave dipole. Your question was answered quite accurately. Cut it in the middle, attach coax and put it up.

 

[prcguy]

In the case of a PVC "T" as a center insulator, if you stick metal pipe elements into the T there will be a gap between the dipole elements and you would connect the coax as close as practical to the dipole ends. If the formula says 18" per side, thats the total length of that side including pig tails from the coax to reach the elements. If you use thin wire for the dipole elements, the lengths from various formulas will be close. If you use thick tubing or pipe for elements the length will usually be shorter.
prcguy

that's not quite what i was asking. does a dipole lenght count from where its attached to a rod or boom or does the measurement stop where the feedpoint is tapped? so if i want a 18 inch element on each side do i cut it for 19-20 inches so when i tap it i would be right? sometimes the feed point is adjusted up or down for SWR's so then the lenght is actually shorter. reason i'm asking is when i make a dipole the first inch or two goes into the pvc T Connenctor and i tap it further up the element. so do i measure the lenght from where i tap it or from the end of the rod in the PVC? it gets confusing when i try to build beams with that measurement hurdle.