[TowerTalk] Common Mode RF choke on a 50 MHz yagi

[David Gilbert]

That's a standard quarter wave coaxial choke that has been in antenna 
books for several decades in one form or other.  I used that technique 
on a triband quad (with separate feedlines) more than 50 years ago.

Off the top of my head, though, I think your version requires that the 
driven element not be isolated from the boom.  Not sure it would work 
with the driver isolated from the boom.  I'll have to draw it out later 
to double check.

73,
Dave   AB7E



On 6/28/2020 3:10 PM, Richard (Rick) Karlquist wrote:
> The simplest way to make a 50 MHz common mode
> choke is to use 56 inches of coax and connect
> one end to the feedpoint and connect the shield
> of the other end to the boom.  Then connect
> your regular feedline to the end of the
> 56 inch cable. Let the coax hang down in a
> lazy "U" away from the boom.  Whatever you do,
> don't be "neat" and tape it to the boom.
>
> I suspect this configuration is somewhere
> in the ARRL VHF handbook.
>
> 73
> Rick N6RK