Air Band Yagi

[KB4MSZ]

Well I got out the antenna analyzer and evidntly it is resonant at around 156mhz.

Cool! Now you can point it at boats.

 

[majoco]

Before you start choppin' and changin' - do a few experiments. Extend the feedline by a quarter-wavelength and check the VSWR again - has it changed by a large amount? Then you're not matched to 75ohms or whatever your feedline's impedance is. Extend the elements to make them right at 125MHz - just solder a bit of wire to each end of all the element. See what that does.

There's a nice little calculator here....

Maple Leaf Communications - Antenna Calculator - 3-Element Yagi

Use our simple calculator to determine approximate dimensions of materials needed to build a 3-element Yagi/Uda antenna, and then shop for your needs on our other pages and select from our inventory of aluminum, fiberglass, coax, connectors, and other parts and accessories for amateur radio and...

www.mapleleafcom.com

 

[Ubbe]

A standard dipole are 72 impedance but your placements of the elements that you have soldered the coax to overlap each other and makes it difficult to know what the outcome will be of that arrangement. 3:1 means that the actual impedance are 3 times from the sources impedance. So probably 150 ohm or 17 ohm which indicate some major issues with the design. The lenght are measured from tip to tip and you might have measured each single element before attaching them to the boom.

/Ubbe

 

[KevinC]

Are you using that old coax you asked about in your other thread?

 

[UlteriorModem]

Are you using that old coax you asked about in your other thread?

Yea, I megged it out and it was fine. The basic issue is that it is not resonant and the desired frequency.

 

[Ubbe]

Yea, I megged it out and it was fine.

That's only a DC check and not a check of what's happening at radio frequencies. Even at SWR 3:1 you should receive better than you do so could still be a coax issue. Get some cheap RG6 just to rule out the coax from the equation.

/Ubbe