I purchased the Radio Shack Pro-82 as my first scanner. Works reasonably
well with the included antenna. I bought an external antenna from Radio
Shack and when I hook it up I often get noise that overrides all channels.
The noise starts out with two very loud tones and then it sounds like a
phone conversation in the background and often the loud tones repeat. The
seems to happen in bursts of a few minutes and basically the scanner is
useless during this activity.

My only theory is that its somebody talking on a Nextel phone(?)

Any ideas on what it is and what I can do about it?

John