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I was thinking of operating an Icom IC-208H with a mobile whip antenna attached directly to the antenna jack on the rear panel. The power level would be a maximum of 20 watts.

I called Icom to discuss the maximum physical size of the whip antenna. I was told it wasn't recommended to attach an antenna directly to a rig because rf may get back into the rig and that an antenna should be separated from the rig.

1: At 20 watts, what's a minimum separation between the rig & antenna so rf doesn't get back into the rig?

2: Why doesn't rf from the antenna on an hand-held get back into the circuitry?

73!

N9LCD

N9LCD wrote:I was thinking of operating an Icom IC-208H with a mobile whip antenna attached directly to the antenna jack on the rear panel. The power level would be a maximum of 20 watts.

I called Icom to discuss the maximum physical size of the whip antenna. I was told it wasn't recommended to attach an antenna directly to a rig because rf may get back into the rig and that an antenna should be separated from the rig.

1: At 20 watts, what's a minimum separation between the rig & antenna so rf doesn't get back into the rig?

You'd have to try it and find out. I doubt anyone knows unless they've tried the same kind of antenna on this particular rig. The answer might be 5W or less.

2: Why doesn't rf from the antenna on an hand-held get back into the circuitry?

That can happen. It normally wouldn't with the manufacturer's "stock" antenna because the whole design is optimized to work with that; the ground plane for the flex whips is part of the circuit board design, or in some cases part of the case design. A mobile rig doesn't include such a feature, and will try to use the chassis and covers (if they are electrically bonded and conductive) as a ground plane, which may work to some degree.

Thanks for your comments!

Not wanting to host either a QRM party or a smoke party, I scrubbed my plans.

73!

N9LCD