Author Topic: RF killing RR box at Remote.  (Read 10329 times)

bigchimp

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Re: RF killing RR box at Remote.
« Reply #15 on: 2016-09-20, 02:57:15 »
Perhaps it's best to start at the source of the RF radiation, the feedline. Many 1:1 isolation baluns offer poor common mode impedance to stop feedline radiation.

A simple balun with 5-6 turns of coax through several mix 31 snap-on ferrites at the antenna feedpoint is a good place to start. It shouldn't be too difficult to get 2000-4000 ohms of resistive  choking impedance. Some cheap baluns offer only a few hundred ohms and consequently work poorly. Shooting for at least 2500 ohms resistive is a good idea.

Once the feedline is properly decoupled with multi-turn mix 31 common mode chokes, the same method will work well for any other wiring in the system that needs decoupling.

In my own system, every cable is choked for RF. My feedline is choked with around 10,000 ohms resistive at 80M and no RF issues. Unbalanced antennas or balanced antennas that are unbalanced due to installation variables will require much more choking.

More power requires more choking. Common mode current increases to the square of the power increase. Double the power generates four times the common mode current.

As mentioned in other posts there are some excellent articles available. Many hams fumble around dealing with RF issues. Grounding is important from a safety standpoint but is almost irrelevant with respect to RF ingress. Proper decoupling - RF choking - is the correct way to deal with this.

Ian
Vancouver BC