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Well, that's not exactly right. If adding a coaxial balun alters the resonant frequency of your antenna, that is a sure sign that you needed the balun because the coax was radiating. RF traveling on the inside conductor of a coax cable is not effected by forming a coaxial balun since it is shielded. The coax shield will block the induction effect from reaching the center conductor when forming the coil. Only the outside braid experiences the choking action.

You mention a valid point about coiling high power cable because too sharp of a curve can cause the insulation to fail. Most quality cable will list the minimum bend radius of the particular cable in the specifications. Some antennas used at high power will benefit from the use of a coax choke to reduce feed line radiation.

The easiest way to see if you need a coax balun is to move your coax away from the mast at the base of the antenna. If you can see a change in VSWR as you move the coax away from the mast or towards the mast, it is radiating and a coax balun will help. Adding one in these cases will restore the antennas desired radiation pattern and reduce RFI. My means of testing will not spot all cases of radiating coax however, it's a great first indicator.

<blockquote data-quote="Shockwave" data-source="post: 157831" data-attributes="member: 10882">Well, that&#039;s not exactly right. If adding a coaxial balun alters the resonant frequency of your antenna, that is a sure sign that you needed the balun because the coax was radiating. RF traveling on the inside conductor of a coax cable is not effected by forming a coaxial balun since it is shielded. The coax shield will block the induction effect from reaching the center conductor when forming the coil. Only the outside braid experiences the choking action.You mention a valid point about coiling high power cable because too sharp of a curve can cause the insulation to fail. Most quality cable will list the minimum bend radius of the particular cable in the specifications. Some antennas used at high power will benefit from the use of a coax choke to reduce feed line radiation.The easiest way to see if you need a coax balun is to move your coax away from the mast at the base of the antenna. If you can see a change in VSWR as you move the coax away from the mast or towards the mast, it is radiating and a coax balun will help. Adding one in these cases will restore the antennas desired radiation pattern and reduce RFI. My means of testing will not spot all cases of radiating coax however, it&#039;s a great first indicator.</blockquote>

[QUOTE="Shockwave, post: 157831, member: 10882"] Well, that's not exactly right. If adding a coaxial balun alters the resonant frequency of your antenna, that is a sure sign that you needed the balun because the coax was radiating. RF traveling on the inside conductor of a coax cable is not effected by forming a coaxial balun since it is shielded. The coax shield will block the induction effect from reaching the center conductor when forming the coil. Only the outside braid experiences the choking action. You mention a valid point about coiling high power cable because too sharp of a curve can cause the insulation to fail. Most quality cable will list the minimum bend radius of the particular cable in the specifications. Some antennas used at high power will benefit from the use of a coax choke to reduce feed line radiation. The easiest way to see if you need a coax balun is to move your coax away from the mast at the base of the antenna. If you can see a change in VSWR as you move the coax away from the mast or towards the mast, it is radiating and a coax balun will help. Adding one in these cases will restore the antennas desired radiation pattern and reduce RFI. My means of testing will not spot all cases of radiating coax however, it's a great first indicator. [/QUOTE]

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