[Boatanchors] Ferrite Choke

[Gary Schafer]

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Ron Youvan
> Sent: Sunday, July 15, 2012 8:30 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Ferrite Choke
> 
>    Dennis D.  W7QHO  mac wrote:
> 
> > Might be interesting to put the antenna up without any choke or
> > ferrite and see how it works out......
> 
> 
>    That is all that existed B 4 antenna baluns were created.
> The advantage of any kind of balun at the feed point of a dipole is to
> prevent a nearby object to
> one half of a dipole from unbalancing the antenna.  If it is equal
> lengths and really in the free
> and clear it does nothing of any great use.  Baluns can be made with
> powered iron also cores.
> --
>     73 Ron KA4INM 

Consider that a coax cable feeding an antenna is actually 3 wires. 
Two inner conductors (center wire and the inside of the shield) and the
third conductor is the outside of the coax shield.

When connected to a balanced antenna, the center conductor is connected to
one side of the antenna and the other side of the antenna is connected to
the inner shield and the outer shield.
That makes the antenna have one leg on one side and two legs on the other
side, one being vertical (the coax). 

This unbalances the antenna and causes current to flow on the outer shield
of the coax which acts as part of the antenna.

It may work very well in this configuration as many have for lots of years. 
The disadvantage is the vertical part can pick up more noise and put RF back
into the shack on transmit. It disrupts the dipole pattern if you care about
that.

The commonly used balun acts as a choke to isolate the outer coax shield
from the leg of the antenna that is connected to the shield.

73
Gary  K4FMX