Wires from SO-239 to Driver on Yagi

[WSAR863]

Does the wire running from the SO-239 to the driver elements of a yagi need to be made of shielded coax or can any wire work? I would think using plain, unshielded electrical wire would make it part of the radiator/driver.

[Sshannon]

24 minutes ago, WSAR863 said:

Does the wire running from the SO-239 to the driver elements of a yagi need to be made of shielded coax or can any wire work? I would think using plain, unshielded electrical wire would make it part of the radiator/driver.

You’re right. The wire leading from the center tap of the SO 239 becomes part of the radiating element. For that reason they are usually connected directly to the radiator or with a very short wire.

[WSAR863]

Thanks @Sshannon!

Got a couple more questions, if you have a couple minutes to humor me.

Does the coax from the connector to the driver need to be a certain portion of the wavelength, or does it not matter? I used RG8x @ 50 ohms.
Where should the feed point be on the dipole driver? At the very end or do I need to try to find 50 ohms?
Will it be less than 50 ohms, if on the very end, closest to the center of the dipole driver? If so, does that matter? Will it impact the SWR if it's lower than the feed line's impedance of 50?

[Sshannon]

Remember, as soon as that wire leaves the coax, it becomes part of the radiator. Any length there either adds or detracts from the radiator. 

A dipole radiator has a length of one half of the wavelength times the velocity factor, and then tuned for the lowest VSWR.  Dipoles are usually (but not always) split in half and the shield is attached to one half and the center conductor attaches to the other half. Both shield and center conductor are attached to the inner ends of the two quarter wave halves of the dipole. 

I don’t understand how you would have long wire anyway unless you use a balun and feed the dipole with ladder line. 

[Sshannon]

34 minutes ago, WSAR863 said:

Thanks @Sshannon!

Got a couple more questions, if you have a couple minutes to humor me.

Does the coax from the connector to the driver need to be a certain portion of the wavelength, or does it not matter? I used RG8x @ 50 ohms.

Coax should always be as short as possible. Tuning the coax to a wavelength is not necessary.

34 minutes ago, WSAR863 said:

Where should the feed point be on the dipole driver?
 

At the center where the two quarter wave halves of the radiator come together, unless you use a gamma match or delta match. I don’t know them well enough to attempt to explain them. 
 

34 minutes ago, WSAR863 said:

At the very end or do I need to try to find 50 ohms?

Straight dipoles are usually about 73 ohms at the center. If you have an analyzer you can splay them slightly like an isosceles triangle. That’s a delta match I think. 

34 minutes ago, WSAR863 said:

Will it be less than 50 ohms, if on the very end, closest to the center of the dipole driver?
 

In an inverted vee configuration you can reduce the impedance to about 50 ohms, but usually Yagi antennas have straight radiators. 

34 minutes ago, WSAR863 said:

If so, does that matter? Will it impact the SWR if it's lower than the feed line's impedance of 50?

I doubt you’ll see less that 50. I wouldn’t worry about it. 

[WSAR863]

Great answers. Thank you!

[WSBZ540]

If you are interested in building a yagi specific to gmrs, I have some designs I've come up with that have their gains spread between 462mhz and 467mhz. If you have a 3d printer, I have parts drawn for a gamma match that takes most of the guess work out of the build.

You can either build it with no understanding of what's going and just follow instructions, or you can deep dive in it. I'm just saying you won't need some super antenna theory under your belt to build it if you don't wanna.